Prepare Flights

User Manual — Plan, Brief, Fly & Log

1. Welcome & What This Is For

A browser-based weather, airport and flight-planning tool for general-aviation pilots. It puts the airports of Europe and its surroundings (some 3,700) on one map under a complete suite of aviation weather forecasts — current conditions, multi-day forecasts, fog, icing, turbulence, convection — to answer the questions before a flight: Is the weather flyable? Where? When?

It is a Progressive Web App: open it in any modern browser, optionally add it to your home screen, and it behaves like a native app (works offline, full-screen on mobile).

2. The Interface at a Glance

A few buttons in the four corners; the map fills the rest. A desktop and a phone differ only in where the Views button sits and whether the views are listed on the map.

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There are no separate layer menus. Charts, forecasts, observations and the Nordic low-level forecast, once separate buttons, are rows of the one Layers tab, grouped by your question rather than by supplier (Section 10).

2.1 Moving Around the Map

Smaller airports appear as you zoom in: large ones from zoom 5, medium from zoom 6, small from zoom 7.

2.2 Searching for Airports

2.3 Asking a Question (Ask)

Ask is a chat that answers questions about the app, an aerodrome and the rules of the air, and shows its sources. Signed in only (Section 3); signed out, Ask opens the sign-in card.

What it does not do. Read the weather (METAR, TAF, forecasts), area or route NOTAMs, airspace activity, your route, flight plans or logbook, or say whether a flight can be made. Asked, it says so and points to where the app shows them, such as the airport popup’s Weather tab or the leg’s Brief (Section 17.4). It is not an official briefing, legal advice or an authority’s view.

3. Signing In & Syncing Your Data

The map works without an account. Signing in unlocks planning, logging and the AI features, and your flight plans, routes, aircraft, views and logbooks then follow you across devices and browsers. The menu lists every feature either way; one that needs an account opens a card offering to sign you in.

3.1 The menu button

One round button in the bottom-left corner holds the account and everything the app keeps off the chart: a person icon signed out, your initial on blue signed in. The menu opens upward, so its bottom is nearest your thumb.

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• Signed out, Flight plans, Logbooks, Flown track, Weight & Balance and Settings are listed to show what an account gives; each opens the sign-in card instead.
• In flight (tracking HUD up) the button stays put; like every map control it grows for a thumb and is drawn as an outline (Section 20.2.1).

3.2 Two ways to sign in

Either way, one account: the first sign-in with an address creates it. A session lasts a year per browser and renews as you use the app; you sign in again only after logging out, clearing cookies, or leaving that browser unused for more than about six months.

3.3 What syncs to the server

Signed in, this follows your account to every device:

Sync runs in the background: on every reload, when the tab regains focus, and periodically. There is no “Save” button.

3.4 What does not sync

3.5 Logging out

Log out in the menu does four things in order:

1. Sends anything not yet on the server: pending edits and whatever was queued offline. If something cannot be delivered (no network, or refused), it says how many changes are unsent and asks first, since logging out would delete them from this device for good: Cancel, and log out once back online.
2. Tells the server to invalidate your session.
3. Clears your account’s copies from this browser’s storage (saved flight plans and the one open in the planner, aircraft profiles, the pilot logbook, the aircraft log, flown tracks, saved routes, views, favourites, W&B loadouts, the Pilot details and synced settings), so the next person on this browser sees none of it.
4. Reloads the page, signed out, so the flight you were planning does not stay on the map.

Sign back in, here or elsewhere, and it is all fetched fresh: nothing is lost, only hidden between sessions.

4. Settings

Who you are, what you fly, how the map and the in-flight view behave, and the services you connect. Open it from the Settings row (gear icon) of the bottom-left menu (Section 3.1).

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• Each page has a ‹ back arrow in its header. A group with nothing for you is left out.
• Close with × or a click outside. Escape steps back one page; on the home list it closes.
• Each section of a page is a box, its name above it, and on the right where it is kept: This device (tablet and phone can differ) or Synced (to your account and your other devices at their next sync, Section 3.3). Mixed sections say neither. Signed out, all is this device’s.
• For signed-in users; signed out, the row asks you to sign in. Most settings go to your account; the few per-device ones are listed in Section 3.4.
• About is not in Settings but in the bottom-left menu, for everyone (4.6).

4.1 Map

What belongs to no single layer. Mostly this device’s; a change shows on the live map at once.

Where MapLibre GL cannot run, Classic: always without WebGL 2; and after the map has stopped the app twice in a row, with a card on the map offering to try again (for the session only if you chose MapLibre GL yourself). The printed briefing always uses Classic.

4.1.1 Layer settings — on the layer, not here

A layer’s options (labels, style, filters) open from the ⌄ on its row in the Views window’s Layers tab (Section 10) or from its chip in the layer strip, bottom-left (Section 11.6b). Not in Settings any more: they belong to a view and are saved and restored with it (Section 9.4). For reference (def. = default):

4.2 Aircraft

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Final reserve and contingency are your fuel policy (Settings › Pilot › Fuel policy, 4.7), by the rules flown; an aircraft can only raise them (4.3), for a club rule, say. Taxi belongs to the aeroplane. The Flight Planner, the briefing and a route’s fuel option read the same figures. Flight rules are set on the flight or route, not preselected here.

4.3 Aircraft editor

Five groups, one open at a time; a closed one sums itself up in a line. Performance drives the planning math; identity and filing feed the flight plan, each leg’s Email handling and Announce flight (Section 17.7) and autorouter. Fuel is shown and typed in the aircraft’s Fuel unit, stored in US gallons.

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• ⤓ Import from autorouter: the editor then says how many fields changed and marks them (3 changed on a closed group). Review, then Save; Cancel discards the import.
• A preset’s reserve or taxi is an override like any field and acts at once: an open route bar re-reads its aeroplane and req moves as you save. A built flight plan keeps its own copy (Section 17.2); Reset to aircraft on its aircraft block pulls the new figures in.
• Save writes the aircraft (or override) to your account and refreshes an open Flight Planner picker at once. Cancel discards changes and returns to the Aircraft page.

4.4 Autorouter (connect your account)

With your autorouter.aero account connected, the Flight Planner finds and validates IFR routes and files flight plans, always under your login, never a shared one.

An expired session asks you to reconnect. The connection is your account’s and follows you to every device you sign in on.

4.5 NOTAM Calendar (subscribe on your phone)

A private, always-updating calendar of NOTAMs for your ★ favourite airfields (Section 6.7), for iPhone Calendar, Google Calendar or any webcal / ICS reader. A closure is an entry over its active period: “is the field open this weekend?” without opening the app.

Signed in only (the feed is tied to your account’s synced favourites): Settings → NOTAM calendar → Create my NOTAM calendar.

4.6 About

From the About entry at the top of the bottom-left menu (Section 3.1), signed in or not; not inside Settings.

Neither Reload nor Repair touches your flight plans, logbook or settings.

4.7 Pilot

All synced.

4.8 Planning

What a printed briefing includes (the weather overview page, the navlog) is chosen on the briefing’s toolbar, where you print it (Section 17.8).

4.9 Track my flight

The in-flight view (Section 20). Per device (tablet and phone can differ); changes apply at once, mid-flight too.

4.10 Notifications — the flight-plan watch

Signed in, the server watches your flight plans and shows what it finds in the app. With the app closed it reaches you on this device (push; iPad or iPhone: the app added to the Home Screen) and/or by email, once turned on.

A message says what changed and which way (EFKU arrival worse: VMC → special VFR), the figures behind it, and what it does to the Brief. Against the briefing you accepted for the leg, its answer then and now:

Brief accepted 07:02Z: Yes, with care — Route → No — Aerodromes · caution: Route

• None accepted: the row it moves (Brief: Weather now red).
• Better news does not claim the answer lifted (the row may be amber for more than what cleared), so it asks you to open the Brief.
• A tap opens the leg’s Brief: Since you last looked lists the messages, Since you accepted the briefing compares every row with what you accepted.

5. Airport Markers

Every aerodrome is a dot coloured by its size, or a lettered badge coloured by its flight category when there is weather to show. What a marker shows, when fields appear and which are left out are settings of the Airports layer.

5.1 Marker Types & Visibility

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Thinning out

Where two fields would overlap (Luton on Stansted, Le Bourget on Orly at zoom 6), the more important keeps its code. The other becomes a bare dot, losing code, fog tag and wind chip but keeping its category colour, or is left out where the two dots themselves overlap. Dots are placed first, so a code never costs another field its dot: beside a small field’s dot, the large airport’s code gives way. Fields come back as soon as zooming in makes room.

Weather shown as

The wind chip points the way the air is moving (downwind, the opposite of a barb), gives the speed in knots, and repeats the speed as a colour: blue under 5 kt, through teal, green, olive, amber and red, to magenta at 50 kt and above. Calm and variable show the number alone. A reported gust hangs off the end in its own colour (G25).

Markers and views

The four display settings travel with a view (Section 9); change them and save the view to keep them. The filters never do.

On the Aeronautical basemaps, zoomed in close, the marker gives way to a windsock from the latest METAR wind; the spot still opens the airport popup (Section 10.10).

5.2 Live Flight-Category Colour

With Flight category (the default) or Category + wind, the dot becomes a larger category badge with one letter:

The worst case wins: whichever value is in the lower category sets the letter.

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None of this needs the Spot forecasts layer (Section 11.1) or any other overlay.

Keeping the colours fresh

• A background pull about every five minutes, and at once when you pan or zoom to new airports or return to the tab after a couple of minutes away.
• “Updated N min ago”, bottom right: green under 5 min, amber under 15, red older. From amber a Refresh button beside it refetches the map’s observations and nothing else. For every weather product and data file fresh, Reload app under Menu › About.
• Below zoom 5 there are no markers to colour, so pulling stops and the indicator hides; both resume as you zoom back in.

5.3 Fog & Mist Badges

A fog or mist code in the METAR adds a small tag under the identifier:

5.4 Filtering Which Airports Show

The filters are options on the Airports layer, in two places only: its row in the Layers tab (⌄) and the Airports chip in the rail, under the type key (4 in Figure 5.1).

• A field must pass every active filter. Favourites are exempt: a starred grass strip always stays.
• Fuel and PPR come from the cached AIPs: only as current as the last AIP refresh, silent on opening hours and whether the pump works. No PPR note is not permission.

The count is the guard: All 3 600 airports shown, turning amber once a filter hides anything:

3 118 of 3 600 shown — 482 filtered out

Filters are remembered between sessions and, signed in (Section 3), synced: a field can be missing on the tablet because of something set on the phone three weeks ago.

6. Airport Information

Click or tap any airport marker and its panel opens: the weather there now and to come, how the field works today (service, hours, NOTAMs, runways), its AIP and its charts. The panel opens centred on the screen and the map stays exactly where it was: popups never pan the map. A long panel scrolls inside its card rather than running past the screen.

6.1 Header

Two rows that read like a quick-look briefing, then the place and the sun.

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6.2 Tabs

Weather · Info · NOTAMs · Charts · AIP · Airgram · Webcams. The panel opens on Weather. Every tab is always offered except Webcams, which appears only for fields in and around Finland.

The NOTAMs tab

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Timetables are read out as a table. An hours NOTAM (tower, AFIS, aerodrome, fuel) keeps its lead-in (VAASA TWR/APP OPR HR:), says where now falls (Open now · until 11:20Z, Not available now · from 14:00Z) and lists the hours day by day from today: three days, the rest under N more days, past days left out. A day called CLSD reads closed; what follows the timetable (a phone number, ADDN OPR HR O/R) follows it here too. An item D) schedule is laid out the same way, under a line saying whether the NOTAM is active right now or when next. A timetable with any unreadable part (a typing error in the times, say) is shown as published.

• The list scrolls inside its card, so a long NOTAM block does not push the panel past the screen.
• The leg Brief tab and the printed briefing use the same cards, read against the aerodrome’s own departure or arrival time instead of now (until 22 Sep 11:00Z · ends 2 d after departure). A timetable there starts from the flight day, and the printed page shows that day’s hours only.

The AIP tab

A plain-language GA summary of the official AIP AD 2 entry (fuel, access / PPR, hours, arrival aids, ground handling, regulations, practicalities), with the amendment it was read from (an AIRAC number or an AMDT); where there is no AD 2 data the tab says so. AI-generated; always verify against the official AIP.

6.2.1 Info tab

Ordered by how soon you need the thing: what is true now, what is different today, then the reference data that does not change. It uses the Weather tab’s boxed sections (a coloured rule along the top, a small-caps heading, the count at its right end: 7 channels, 3 runways), so a section can be skipped unread. The rule is blue for radios, amber for the ground, slate for the runways.

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Is the service there now? The hours beside the heading say Open in green or Closed in red, with the time it changes in grey (Closed · opens 20:45Z). The state is read from whichever schedule the aerodrome has: the hours NOTAM where it could be parsed, otherwise today’s row of the Hours card.

The chip is always now. With the time bar off Now, an outlined second line marked ⏱ gives the state at that time (⏱ Fri 6 Nov 15:00Z · Open · until 15:20Z), and the Hours card marks that day, that instant (a blue line on its strip) and that window (blue) beside now’s red; past the days the card lays out it says not known. Both follow the bar and go when it is back at Now.

Where each fact is printed in the AIP. The headings of Radios (where the full list opens), On the ground and Runways end with their AD 2 items: AD 2.18; those of the ground rows shown, up to AD 2.3 · 2.4 · 2.7 · 2.20; AD 2.12 · 2.13 · 2.14. An opened ground row ends with its own (Fuel AD 2.4, Winter AD 2.7). A tap opens the full AIP at that item. Shown only where the aerodrome has a full AIP the app can open; they name where the AIP says it, also for a value filled in from OpenAIP.

The NOTAM line sits under the snapshot, and only when a NOTAM in force now can change the day.

The NOTAMs tab’s button carries the same count, in the colour of the worst one.

Hours (UTC) is one card for what is known about the opening hours, under the NOTAM line. Services (fuel, handling, de-icing) keep their hours on the On the ground rows.

Hours NOTAMs are read in the shapes the states write them: Finland’s one group a line with commas; Estonia’s groups without commas, with an EXC: day whose hours replace the usual ones; dates as NOV 09 or 09 NOV. What a NOTAM adds after its schedule is shown under the table.

Radios are folded away by default; the snapshot shows the two channels you dial. all N radios opens the full list directly underneath, in call-sign order (ATIS, air, radio, ground), each call sign and frequency a tight pair with the decimal points lined up; press again to fold it. The channel the snapshot lifted to the top is marked primary. An aerodrome with nothing beyond those two channels has no link and no folded block.

Runways come last: a drawing, a table and a line about night lighting.

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The table’s columns are RWY · Size · Surface · Declared · Aids. Size is length and width in one cell (2700 × 45 m, AIP figures where published), with the PCN beside the surface.

The drawing is made where the AIP publishes threshold coordinates (AD 2.12): true relative positions, true lengths against each other, and the angle and place where runways actually cross. Unlike the Weather tab’s wind rose, a compass of runway bearings, it is a map: it shows whether two runways meet at their midpoints, near one end or not at all. It uses the basemap’s own language, so panel and aerodrome look like one thing: the surface in the colour of its material (dark for asphalt and concrete, green for grass, grey where the AIP states no surface, never tarmac by default), a white dashed centreline, the length along the runway. A displaced threshold is a bar across the pavement where landing may begin: the distance you do not have is a gap you can see.

• The bearing. The AIP publishes the TRUE bearing; the magnetic comes from the magnetic-variation grid the navlog and the map ruler use, and the tooltip gives both numbers and their sources. The two-digit designator rounds to ten degrees, and the variation moves under it between cycles without the paint changing.
• No wind in this section, by design: the Weather tab draws it against these same runways, with the favoured end and the components against the warning ladder, and one question should not get two answers on one screen. This section is the field: dimensions, surface, strength, declared distances and aids.

OpenStreetMap is volunteer data and can be out of date: for taxiing, the georeferenced aerodrome chart in the Charts tab is the official drawing.

Links at the foot of the tab: Map (Google Maps at the field) and, for Finnish GA fields, Lentopaikat. The homepage is under Contact, not here.

6.3 Weather Tab

Boxed sections, each with a coloured top stripe naming its source, in this order: Summary (lavender, only once you ask for it), METAR and TAF (blue), Model — Now (green), Model — Forecast, LLF (magenta, Nordic) and the text Area forecast (Norway and Latvia). When any forecast layer is on (Winds, Icing, Turbulence…), an Active weather layers verdict block ends the tab, as in Section 7.

A jump bar is pinned to the top (12 in Figure 6.1): METAR · TAF · Model — Now · Model — Forecast · LLF · Area fcst, the sections that loaded for this field, shown when there is more than one. Press one to jump to it; the current one stays highlighted as you scroll, and section headings pin under the bar, so the block you are reading is always named. At its right end sits Ask AI (signed in: the AI features need an account, Section 3). The Summary is not drawn until you press it; then it opens at the top of the tab with a short plain-language briefing built from METAR, TAF, hourly Open-Meteo and (Nordic only) LLF, in two paragraphs: the current and next few hours, then how the day evolves. UTC times only.

The TAF has its age on the right, a TAF / 1H toggle and a timeline of one column per forecast period (or hour), each with a flight-category badge (Reading the forecast grid, below). Its raw text is folded behind the header’s RAW button and appears on the line under the heading; every popup starts folded.

Fresh reports. The METAR and TAF headers each carry a ↻ refresh button that bypasses every cache layer and pulls the freshest report from the source, for an overdue observation, without reloading the page (the TAF’s only when the field has a TAF). The popup also refreshes its METAR on a timer while open, and the age timestamp turns amber, then red, as the reading ages.

The METAR block

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The two pictures sit side by side, always the same height, and are drawn the same way in the Model — Now block so the two can be compared directly.

Wind is not a chip but the rose, where speed, direction and what they do to this field’s runways are one thing. The components warn on one ladder shared with the map’s Print briefing (its runway column), the flight plan’s briefing, the Brief and its wind alerts:

• The gust’s crosswind is judged on the same scale and shown next to the mean (cross 12–19 kt R): it is the component you actually fly in the flare.
• These are fractions of the type’s demonstrated figure; a per-aircraft limit is planned.
• A ladder, not a yes/no “strong wind” badge: wind strength is continuous, and 25 kt down the runway is not 12 kt across it.

Trend (landing forecast). A BECMG / TEMPO / NOSIG group gets its own line under the chips, in words:

TREND until 1150Z — MVFR — temporarily: visibility 7km, showers of rain

• The validity end is spelled out: a trend runs two hours from the observation.
• The badge is the category the trend would produce, computed against the observation, because a trend lists only what changes: a TEMPO that mentions visibility but not cloud keeps the cloud that was observed.
• NOSIG reads “no significant change expected”, in grey.

The model blocks

Model — Now is the model’s reading of now; Model — Forecast, a section of its own because it answers a different question, is its TAF-style forecast table. They are named for the model and the horizon, not the vendor, so that neither claims the word “Forecast”, which belongs to the official forecast. The source line in each heading names the model actually read (ICON-EU under Weather: Europe inside its box, ECMWF elsewhere) and the run (run 15Z; Section 11 explains run 15Z · map 12Z). Both are drawn like the real METAR/TAF, and both are always a model estimate, not an observation.

Fog the model draws but does not name. Open-Meteo’s weather code never reports fog over the Nordics: across 4013 station-hours at 20 Finnish aerodromes it was never once 45 or 48, even in hours its own visibility said 240 m. So fog is read from the model’s visibility and humidity: below 1000 m with humidity at or above 95 % gives an FG badge (FZFG below freezing) and a present-weather chip. It decodes a figure the block already shows, so it can only appear in an hour the category row already calls LIFR from that same number.

• No mist tier: a BR badge on the 1000–5000 m band would have fired 297 times per 4013 hours and been right 8 % of the time.
• Low visibility without the humidity for fog leaves the sky glyph blank rather than drawing the clear sky the weather code claims.

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• How far out fog is marked. The FG badge is read for the first 60 hours only, the reach of the fine 2.5 km Nordic model, the only one in the blend with a real visibility field. Beyond it runs a coarse global model nothing here has checked against observations. An empty warn row that far out means not assessed, never “clear”, and a note under the table says so.
• Greyed visibility. A visibility in the 3–8 km band with no humidity or precipitation behind it is drawn grey, italic and without its category underline: shown, but not allowed to set the category. The model lands there about one hour in eight, and in those hours the field was 9999 or CAVOK 87 % of the time; six kilometres alone would paint MVFR. The airport marker’s category dot follows the same rule, so dot and block agree.
• Where the field has a TAF, the TAF is the forecast and this table a model estimate beside it; where they disagree, neither is suppressed.

LLF and the area forecast

Low Level Forecast (LLF), Nordic only. A compact table with one column per 2-hour window (12-14Z, 14-16Z…), the current one marked NOW. Empty future windows are hidden, and the section disappears entirely outside Nordic LLF coverage. Plain-English overview text sits underneath.

A row that is empty in every column is left out, so a quiet forecast may show only G, VIS and CLD. All band-type rows are filtered by point-in-polygon to the airport’s exact coordinates, so distant zones in the same FMI area do not leak in.

Area forecast (text), Norway and Latvia only: the two states the graphical Nordic LLF does not cover (Section 13), so for them this is the low-level forecast. It is the telex as published, unreflowed, in a monospaced block, because a GAMET’s WIND/T table is read down the levels. The header line gives the bulletin id, issue time and publisher. Nothing appears for other countries, nor in the click-anywhere popup: it is a field briefing item, not a map layer.

• Read the bulletin’s own area line. The four IGAs describe coast, fjord and lowland areas and do not tile the country: the inland mountains between 61 and 62 N east of 7°30′ are in none. Such a field gets the nearest bulletin with its IGA PROG … area line intact, so you can see whether you are inside it.
• The leg briefing’s Enroute block ends with one collapsed Area forecast row per bulletin the leg touches, from its aerodromes (departure, any airport stop, destination) and the alternate: a Norwegian destination with a Norwegian alternate 300 NM north gets both. Open the row for the text. A leg that only overflies Norway gets none: the bulletin is chosen by an aerodrome’s ICAO code.
• The printed briefing has it on the Area weather page beside the SWC and the SIGMETs, open and in full and once per bulletin, not per airport: three Latvian fields sharing FALV51 get it once, all three named above it.

Reading the forecast grid

The TAF and Model — Forecast tables are drawn by the same code, one grammar for both, so everything below applies to each. Time runs left to right, one column per hour or period; the row labels stay pinned on the left while the columns scroll.

The warn row

Everything that is a hazard rather than a measurement collapses into the last row. A blank cell means the forecast flags nothing; nothing is inferred beyond what the source states. Colour groups the family (convective, freezing, wind, obscuration), but the code is always spelled out, so the row survives a black-and-white print.

A transient (TEMPO / PROB) hazard is drawn hollow: same code, visibly not the prevailing condition. So is a CB or TCU that a BECMG is bringing in, for the hours of its window: it may already be there, and it is not yet the prevailing cloud. From the end of the window it is solid.

Offline. The whole tab, including the two Model sections and the icing, turbulence and convection verdicts that read the model’s pressure levels, works with no connection at every aerodrome in the countries you have selected and at the airports of your packed flights. The stored forecast runs 48 hours rather than seven days, so offline the table is two days long; the Days view still covers three. Everything else reads exactly as it does online. See Section 24.

6.4 How Icing is Detected

An icing badge appears whenever any of these is true:

• The METAR contains a freezing-precipitation code (FZRA, FZDZ, FZFG, …).
• Temperature is in −20 … +2 °C AND there is precipitation (RA, SN, DZ, PL, SG, GR, GS).
• Temperature is in −20 … +2 °C AND ceiling ≤ 5,000 ft AND temperature−dewpoint spread ≤ 3 °C (visible moisture in clouds).

The trigger is deliberately permissive: icing certificates require margin, and a false negative costs far more than a false positive.

6.5 METAR History — the Last-3h Trend

Last 3h in the METAR header (3 in Figure 6.5) opens a table headed “Observed — last 3 h”: how the weather is actually evolving. Is the ceiling lifting or lowering, the visibility improving, the wind backing or building?

Read it against the TAF below: a TAF calling for improvement carries more confidence when the last three hours already show it, and a deteriorating trend against a steady TAF is a flag to watch.

6.6 Unofficial Weather at Fields Without a METAR

Many smaller fields publish no official ICAO METAR. Where a usable observation exists nearby, the app shows it anyway, clearly labelled so it is never mistaken for the real thing: a line above the decoded weather always says where the reading comes from.

So two neighbouring grass strips can differ: one has a station close enough, the other’s falls just outside. Unofficial fields also get the Last-3h trend (6.5), from our own snapshots. Treat unofficial readings as situational awareness and verify against official sources before flight.

No METAR or TAF at all. With neither a report nor a usable station, the METAR section reads “No METAR — no station within 27 nm.” and the TAF section “No TAF available.” with “See Open-Meteo model estimate for TAF below.” The two Model sections (6.3) then give a reading and forecast in the grammar of the real reports: a numerical-model estimate (the data behind the forecast layers), never measured weather, and labelled so throughout.

6.7 Favourite Airports

Mark the airports you check often and reach them, with their weather at a glance, in one tap. Favourites need you to be signed in (Section 3); they then sync to your account and follow you to every device.

The search box lists the same favourites, and the nearest fields too.

6.8 Charts & the Plate Viewer

A chart tapped in the Charts tab opens inside the app, full screen, instead of in a new browser tab. On many charts your own position is drawn on the plate, which turns an aerodrome chart into a taxi aid at an unfamiliar field, day or night.

The chart list

The Charts tab and the viewer’s own chart picker are the same list, so what you learn in one works in the other.

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Temporary arrangements lead the list. Works, temporary runways and their procedures are published as AIP supplements, not in AD 2. They head the list under Temporary, each with its number and dates in force, because a supplement overrides the chart it amends. They go when they expire; one not yet started is greyed. Refreshed daily.

Four ways in

The last three skip finding the field on the map. The chart that opens first depends on the aerodrome’s role: the aerodrome chart (with the taxiways) for a departure; the visual approach chart, then the instrument one, for a destination or alternate. The title and the ‹ › arrows reach every other chart at that field.

Which charts can show your position

Several states publish georeferenced AD 2 PDFs: the projection is inside the file, so the app places you on the page without altering the chart. They carry the ⌖ in the list.

A chart without georeferencing says “Not georeferenced” in the corner and shows no aircraft symbol. Nothing is guessed.

Moving around the viewer

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• The control bar sits at the bottom on a phone or tablet, within reach of the thumb and clear of the camera housing, clock and battery along the top edge; with a mouse it stays at the top. The chart keeps clear of the notch, so “fit page” always means the whole page.

Offline

Charts in a flight pack open with no connection, position and all: the pack carries the chart PDFs, the aerodromes’ AIP AD 2, the georeferencing and the viewer itself (Section 24). A chart or AIP opened once online is kept too. One opened for the first time without coverage, and not in a pack, cannot be fetched; the viewer says it is not on the device.

7. Click-Anywhere Weather

Any point on the map gives its weather: the model’s now and forecast, the Nordic LLF where it covers, and one line per weather layer you have on.

Like every popup it opens centred without moving the map; a small blue ring marks the point. Taller than the viewport (an AI summary, say), it scrolls inside the card.

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7.1 Header

Laid out like the airport popup’s, with the location in place of identifiers.

7.2 Sections

Boxed sections follow, each with a coloured top stripe for its source. The model leads, as it covers the whole planet; LLF follows only inside a Nordic forecast area, and elsewhere neither section nor button appears.

7.3 Active Weather Layers

With forecast layers on, Active weather layers closes the popup: one line per layer at the selected altitude and time-bar offset, following both live. The fastest check that an overlay matches the data at a point.

Only a layer’s model source adds a row (Model; ICON for Convective activity, CAT for Turbulence); LLF, MET NO and FMI add none. Rows marked map read the very cell the layer painted (same model, hour and derivation), so row and colour cannot disagree; until the layer loads they come from the popup’s own point forecast and say point fetch.

8. The Time & Altitude Bars

The time bar at the bottom of the map sets the moment shown by every time-aware overlay and the airport markers at once. It is always there: scrubbed, the markers turn into a TAF or Open-Meteo forecast (Section 5.2), so “what does Friday morning look like over the Baltic?” takes seconds, no overlay needed.

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8.1 The Altitude Bar

Cloud cover, Winds aloft, Temperatures, Icing and Turbulence are three-dimensional, and Traffic can be filtered by level; Precipitation, Convective activity, MSL pressure and Fog are surface or whole-column and ignore the level. With such a layer on, a shared altitude chip sits at the bottom of the map beside the time, naming the level (Auto, Low, FL050…); a tap opens the menu. A level applies to every active 3-D layer at once, keeping comparisons honest.

Low / Mid / High do not overlap: a shear layer or icing cell is in exactly one. Flight levels form a ladder, highest on top. Each button’s hover names what it represents and its pressure level.

All are levels the models publish: 1000, 950, 925, 900, 850, 800, 700, 600, 500, 400, 300, 250 and 200 hPa on ICON-EU, less 950 / 900 / 800 on ECMWF. Open-Meteo documents a 25 hPa grid, but 775, 750, 650, 550, 450, 350, 275 and 225 hPa come back empty from every model, so nothing asks for them.

Sliding through the levels

• Clouds redraw at every level passed, since all levels are on the device, and switch at once, no fade: only published levels are drawn, and the chip names the one on the map.
• Winds, Temperature, Icing and Turbulence redraw when you stop (on release, or a moment after the last step), so a slide starts no download for each level it crosses.
• With no altitude-aware layer on, the chip hides and resets to Auto, so the next layer starts in its default state.
• Switching views keeps the level: like the forecast time it is your session setting, and no view changes it (Section 9).

9. Views

A view is a named set of map layers — “VFR conditions”, “Icing conditions”, “Weather now” — applied in one tap. Forty-five ship with the app, free to everyone; you can save your own, and signed in they follow you to every device. A view of your own can also be printed as a briefing in one click without changing the map you are looking at (§ 9.5).

A view sets every layer at once. What it names goes on, what it does not name goes off, so a view replaces the picture rather than adding to it. That is what makes one tap enough. The view you came from stays one tap away on the bar, so nothing needs an undo. Airports are never switched off by a view.

9.1 The Views button and the bar

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Column or disc: the pointer decides, not the pixels. A mouse and a screen of at least 820 × 600 get the column. A finger — phone or tablet, either way up — gets the disc: on a tablet in the aircraft the map is the instrument, and a permanent column would cost a strip of it. Views on the map, at the top of the Views window’s Views tab, overrides this: Auto, Always show or Button only.

Seeing the map under the weather. Under real weather, a view like Icing conditions (a filled raster, the freezing-level boxes, the official forecast areas) can hide the chart. Two controls answer that; both appear only while a filled forecast layer is on.

9.2 The built-in views

Forty-five, of which thirteen are on the map out of the box: the two charts, what is happening now and what is coming, and the questions asked before most flights. The rest are one tap away in the view list.

• One view answers one question, and its name says which. A combined view says so (Icing conditions: the model, the freezing level and the official low-level forecast). A single-layer view is named after its layer, with the source in brackets where there is more than one: Icing is the model, Icing (LLF) the official forecast, Cloud tops (satellite) the observation. Model and official forecast are separate views on purpose: compare them by switching, not by stacking them until neither can be read.
• A combined view carries at most one filled raster; anything on top of it is lines, symbols or the airport markers. That is why none of them is unreadable.
• A view states every setting it needs rather than inheriting what the previous one left, which is why the same setting appears in several views with different values.

The On the bar column says which start on the map; the eye in the Views window (§ 9.3) changes that. Under each description are the layers the view turns on, and the basemap if it switches one.

Most views leave the basemap alone: they are questions you ask on top of whichever chart you are flying. The exceptions:

Three things a view never sets. The altitude is yours for the session, so switching views keeps the level you are on. The weather opacity is yours per device (§ 9.1). The airport filters (runway length, fuel, PPR) are a standing personal choice, not part of any picture.

9.3 Choosing which views the map offers

The Views window has two tabs: Views, the list of pictures, and Layers, the switches a picture is made of (Section 10). Open it from the map’s stacked-sheets button (on a phone or tablet, Edit… in the views list). It lands on the Views tab, because the view is what you pick and the layers are what you go on to tune. The tab lists every view, the forty-five built-ins and your own: the ones on the bar first, the rest A–Z.

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• The arrangement syncs across your devices. It is a map tool, so it lives here only: Settings › Map ends with a row saying so and an Open Views button.
• A view you save with Save as new… does go on the map: naming a view is as deliberate as it gets. Anything else that arrives in the list (a view synced from another device, say) stays off the bar until you switch its eye on, so the column cannot grow behind your back.

9.4 Changing what a view contains

The Views window is the view editor. There is no editing mode: apply a view, change the layers and their settings as always, and the top row (1–4 in Figure 9.3) offers what to do about it. The row sits above the two tabs. On the Layers tab it is always there; on the Views tab it appears as soon as there is something to save, revert, reset or name.

Your version belongs to the view as it was when you saved it. If a later release changes what that view ships with, your saved version steps aside and you get the new one. Otherwise one Save would silently freeze the view on that device for good. Where the view sits on the bar, and whether its eye is on, are yours either way: that is your arrangement, not its contents.

What a view carries. Its layers, its basemap if it names one (§ 9.2), and those layers’ settings.

The rule for every layer setting: a view that turns a layer on and says nothing about one of its settings shows that setting’s default, never what you last picked somewhere else. So a view that turns Clouds on without naming Cloud cover — edges (anything saved before build 2812) draws them Soft, while the built-in Cloud cover and Cloud base name Stepped and say so every time they are applied. To keep a different choice in a view — ICAO symbols in Icing conditions, say — set it and press Save on the view.

9.5 Printing a view

Open the Menu (bottom-left) → Print › and pick the view. It prints straight away, over the map window as it is now, at the time and altitude you are on, and the live map is left exactly as it was. For a particular piece of ground on paper, put it on the screen and print; for a whole flight, the navlog sheet frames itself on the route (Section 18.3).

10. Map Layers — the Layers Tab & Basemap

Everything the app can draw on the map is a row of one list: the Layers tab of the Views window. The chart under the layers is chosen separately, from the basemap button above it (§ 10.1).

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Radar, Cloud tops and Satellite image are a choice: picking one tag drops the other, and tapping the lit one turns the row off. Each pair shows one thing twice (RainViewer and FMI the same rain, FMI and EUMETSAT the same cloud, the two cloud-top layers one quantity on deliberately one colour scale), so stacking would hide one under the other, not compare them.

Each layer that is on gets a chip in the layer strip at the bottom-left of the map: its colour key and the same settings (§ 11.6b). The chart layers are remembered for the session, so a reload does not wipe the picture. The built-in VFR and IFR views (§ 9) switch the basemap and the matching layer set in one tap.

The rows, and where each is described. This chapter covers the basemaps and the chart layers; the weather rows are in Sections 11–14.

10.1 Basemap

The basemap button at the top of the right-hand stack shows the code of the chart you are on — VIS, ENR, STD… — and opens the picker, grouped Aeronautical, Map and Other, with one line under each saying what you get. A basemap draws a chart and nothing else: it never switches a layer on or off. All except Satellite, Topographic (MML), Outline and State VFR charts are rendered by MapLibre GL JS from OpenStreetMap data via OpenFreeMap, so they zoom smoothly and stay sharp on high-DPI screens; Outline draws Natural Earth coastlines and borders.

On Aeronautical (visual), restyled to read like a visual chart, a frequency panel pins to the corner when you zoom in (on the enroute base too), a windsock appears near a field once you are zoomed in close (from the latest METAR), and the Special Use Airspaces tags surface each area’s code and altitudes by zoom (§ 10.2, 10.3, 10.10).

How the Terminal Airspaces are drawn is that layer’s own Style, not the basemap’s (10.2): the VFR view sets the chart-style bands of Figure 10.6, the IFR view the muted pale yellow that tints the terminal area around ESSA in Figure 10.7. Neither base switches an overlay on: the VFR view and IFR view load the full working sets in one click.

State VFR charts (code ICAO) is behind a feature switch, off unless turned on for you. Then it joins the Aeronautical group: the states’ own ICAO 1:500 000 charts over the visual chart, so the map is never blank where no sheet reaches.

• Under its row the picker lists each chart: Download (edition, size), Stop while it runs, then Update when a newer edition is in force, and Remove. Charts are kept on this device only: a PDF is cut into map tiles here, Switzerland’s tiles are stored as they arrive.
• A card on the map offers the chart under the view, once per session (Not now holds until a reload).
• Where sheets overlap (Latvia’s reaches into Estonia), the chart of the country at the centre of the view is on top. A line at the bottom-left credits the publisher and edition of each chart in view.
• While a chart is prepared (Latvia’s takes 2–3 minutes) the app keeps the screen on, because a locked screen stops the run; the note under the running chart says so when this device does not allow it (Low Power Mode, for one). The map stays usable meanwhile, and the finished chart appears on it at once.

10.2 Terminal Airspaces

10.3 Special Use Airspaces

Restricted (R), Danger (D) and Prohibited (P) areas, plus TSA / TRA reservations (military training, daily AUP/UUP releases), in two independent channels:

• Tags are shown only for areas active now or activating later today; read the rest from the colour. Areas below 1000 ft get no tag.
• Tags size themselves to the map and step aside so they never overlap another tag, a leader line, an airport, an obstacle or a navaid; a tag pushed off its area is tied back to it with a thin line.
• Local training areas. The Finnish AUP/UUP set also holds the aerodrome-local TSA / TRA / CBA (EFTRATP61…95 around Tampere-Pirkkala). They draw faintly (dashed outline) whenever the layer is on; zoomed right in, a subtle label along the inside top edge gives the designator over the upper / lower limits. An active area of any class still fills and tags as above. This is their only source: OpenAIP does not carry Finnish TSA/TRA.

Kaliningrad. The Kaliningrad FIR is drawn here as a permanently active P area, GND–UNL. It is not a Russian designation: Russia publishes no AIP this app can read, so the boundary is derived from the three neighbours that publish it: the Lithuanian AIP (Vilnius CTA) for the north-east edge, the Swedish AIP (Sweden FIR) for the western segment, the Polish AIP for the sea limit and the land frontier. A FIR limit is an agreement under ICAO Annex 11; the three agree to within about a kilometre, and the build fails if they stop agreeing. Its popup carries no AIP reference, and nothing inside is mapped (no CTR at Khrabrovo (UMKK), no TMA, no danger area): there is no source. Russia closed its airspace to aircraft of the EU states on 28 February 2022; the EU applies the mirror ban to Russian aircraft (Regulation (EU) 833/2014, art. 3d).

Sources, in this order of authority:

• The national eAIP ENR 5.1 for Finland, Sweden, Norway, Denmark, Estonia, Latvia and Lithuania, each AIRAC. It wins: OpenAIP’s copy of the same area is dropped (matched on designator across the spellings EK-R39, EN-R116, ESR126); across Finland, 244 of OpenAIP’s 245 areas.
• OpenAIP for the R/D/P geometry of the rest of Europe, and the occasional area the national scrape does not carry.
• Flyk for a Finland-extended R/D/P set (broader than OpenAIP) and temporary areas from NOTAM supplements, made and changed at short notice.
• TSA / TRA / local-training reservation times from AMC Finland’s AUP/UUP (ais.fi, read several times a day) and EUROCONTROL’s EAUP, re-evaluated against the current hour for activation state; Flyk supplies the shapes.

Coverage, freshness and zoom of the OpenAIP-sourced areas. OpenAIP offers no downloadable database and its live API cannot serve a moving map, so the app hosts its own per-country export, rebuilt weekly: 46 European states, Turkey and Cyprus included.

Use it for: avoiding active airspace, planning round military exercise blocks, the NOTAM number before phoning ATC, and which areas reopen during your flight window.

10.4 ACC Sectors

10.5 IFR Points

The published enroute significant points (five-letter name-codes) from the national eAIP.

10.6 VFR Points

10.7 GPS Interference

10.8 Traffic (ADS-B)

10.9 Airways

The IFR ATS route network as lines between significant points, in the openFlightMaps style (Figure 10.7).

10.10 Airports

10.11 AMA Grid

A grid of Area Minimum Altitudes: the lowest altitude that clears terrain and obstacles within each quadrilateral, drawn as a faint number kept behind the other layers (2³ = 2300 ft). Borders are tinted by height band. Click anywhere for the value under your finger.

• Two levels, as on the published AMA chart. Zoomed out: the 1°×1° square in solid lines with one figure in the middle. One zoom step closer, dashed lines divide it into four 30′×30′ quadrants, each with its own smaller figure. In three quadrants out of four that number is lower than the square’s, sometimes by a thousand feet; the square’s figure is simply the highest of its four.
• Computed with the Fintraffic ENR 6 AMA formula over each cell plus an 8 km buffer, rounded up to the next 100 ft:

max(highest obstacle MSL, highest terrain + 60 m) + 300 m

• Terrain from elevation tiles; obstacles from the states’ own official obstacle sets in Finland, Sweden, Norway, Denmark, Estonia, Latvia and Lithuania (Area 1 data files, except Denmark and Lithuania, which print the list in the AIP itself), and OpenAIP elsewhere.

10.12 Navaids

10.13 Obstacles

Individual obstacles with the official Finnish VFR chart symbols (eAIP GEN 2.3), by type, each with its top elevation (ft MSL) below the symbol:

• A lighting mark at the apex when known: a ray-burst for a steady light, a solid five-point star for a flashing one.
• The symbols grow moderately as you zoom in; in a cluster (a wind farm) only the tallest keeps its height number. Hover for type, elevation (ft MSL and ft AGL) and lighting state.
• Source: Finland, Sweden, Norway, Denmark, Estonia, Latvia and Lithuania use their own official obstacle sets, complete and the only source with the lighting state; the rest of Europe comes from OpenAIP (tallest few per cell, no lighting). Refreshed with the rest of the data.
• Use it for masts, turbines and chimneys along a low-level track and near a destination. Advisory; verify heights against the AIP.

10.14 Power lines

Major overhead power lines: a low-level hazard worth seeing for valley routes, ag work or any operation near the surface. Advisory reference only.

11. Weather Forecast Layers

The forecast layers paint the model’s weather on the map (wind, cloud, rain, fog, icing, turbulence, convection, the air mass) beside the official charts and warnings. They follow the time bar (Section 8) and, where the weather varies with height, the altitude chip (Section 8.1): one map for where, when and at what level.

Weather: Europe | Global. While a forecast layer is on, a chip in the map’s bottom-right corner (beside “Updated …”) names the data the layers read; click it to choose. Same setting: Settings → Map → Weather data, kept on the device.

• The brief’s source line names the model: OM 14:00Z (ICON-EU) or (ECMWF), also for a leg beyond ICON-EU’s reach. The forecast table’s reads ICON-EU, global from Sun 13 16Z, with a dashed rule at the first coarser column and a note under the table.
• Both lines carry the run: ICON-EU · run 15Z is the newest the API serves. For twenty-odd minutes after each run, while the tiles are built, it reads run 15Z · map 12Z: popup and map are two runs of one model, both right, and may differ until the map catches up. Hover the line for the explanation.

Opacity. One slider, 20–100 %, for every filled forecast layer: behind the small Opacity · 100 % label at the end of the views column (first row of the views list on a phone) and above the weather groups in the Layers tab, shown while any fill is on. Per device, untouched by views. Symbols, labels and isobars are never faded. Press and hold the Views button to hide the weather while you hold it (Section 9.1).

Keys and settings. There is no legend panel. A layer’s colour scale opens from its chip in the layer strip at the bottom-left (Section 11.6b), one layer at a time, with its settings under it; the same settings are behind the ⌄ on its row in the Views window’s Layers tab. They are set on the layer, not in Settings, because they travel with a view. Settings › Map keeps only what belongs to no layer (map engine, map buttons, weather data) and links to the Layers and Views windows.

11.1 Weather Map

Weather symbols with the temperature under each, on a fixed lattice across the view: where it is clear, clouding over or raining, as a consumer weather map reads. The Spot forecasts row under Air mass & warnings (source Model); the Spot forecasts and Weather forecast views turn it on too. The symbols stay off the airport markers on purpose: the field’s flight-category dot (Section 5.2) carries the aviation category.

Icons and WMO fetch two more fields (visibility, humidity) to find fog, for the first 60 h only; later hours show the model’s code. Emoji fetches what it always has.

Key: the symbol for every weather the model reports, in each set.

Time: at Now the latest ~15-minute nowcast (as the airport popup’s Weather panel); scrubbed ahead, the hourly forecast for that time, out to 7 days. Computed from temperature and WMO weather code sampled from Open-Meteo on the lattice: ICON-EU under Weather: Europe, ECMWF under Global (hourly). Use it for a fast synoptic read and how it evolves over the next hours. Model guidance, not an observation: for live precipitation use the Radar layers (Section 12).

11.2 Winds

Animated particles streaming with the wind at the level on the altitude bar (Section 8.1), faster where it is stronger: the Winds aloft row under Wind & turbulence (source Model). The Weather forecast view draws them with the MSL isobars and H / L centres, the forecast rain, the convective areas with CB / TCU labels and the spot forecasts (Section 11.1); SWC (Model) turns barbs and particles off and keeps only the strong-wind marks (Section 14.1). Use it for picking the most efficient cruise level, spotting frontal shear and judging crosswind for an airport.

• Level: Auto is the 10 m surface wind; Low / Mid / High 850 / 700 / 500 hPa; each flight level its own pressure level, fetched when picked.
• Speed colour: grey-blue below 5 kt, green to 15, yellow to 25, orange to 35, red to 50, magenta above.
• Computed: the model’s wind at the level, sampled on a grid over the view; particles advected each frame by bilinear interpolation, respawning at random to keep the field alive.

Strong wind marks (SWC)

Only the wind that matters, drawn as the significant weather charts draw it, from the whole column FL025–FL180 (not the altitude chip’s level), for the forecast’s first 48 hours.

• A line is traced on its core’s own level, so it follows the particles at that level, and keeps to its band while the wind stays above 40 kt: a short dip does not cut it, and the flags near its ends can read 40 kt.
• Only a band at least 500 km long gets a line (zoomed in, a line running off the view is enough). One band, one line: a weaker band ends where it meets a stronger one. At most five.
• The SWC draws a jet from 80 kt at jet levels; 50 kt at FL100–FL180 is where wind changes a light twin’s plan. A band too short, or the wind round a storm below FL100 (an area, not a jet), gets no mark; at low level the diamonds and the particles show it.
• The marks keep clear of each other and of the aerodromes (nothing on a line, its flags or its arrowhead), step aside for the hazard, cloud, fog, freezing-level and tropopause labels, and the precipitation plates and spot symbols make room for them. Hover a diamond or line label for words; the key shows each mark while they are on.

11.3 Clouds

A smooth cloud-cover raster (GPU-rendered, zooms cleanly) at the level on the altitude bar: the Cloud cover row under Cloud & visibility, source Model (its MET NO source is in Section 11.14). Use it for a quick “is there a hole?”, ceiling height awareness and comparing cover at different cruise levels.

The word speaks for the area around the label, as the Nordic SWC chart writes it: BKN/LCA OVC broken, locally overcast; BKN/OVC varying between the two; OVC/LCA SCT overcast with scattered gaps inside the area (LCA FEW where the gaps are mostly few or clear; only gaps the area encloses, not open sky beyond its edge).

• A minority is named once it covers a tenth of that neighbourhood; an overcast core of three cells or more always is, with a label on it. Overcast is placed before broken, so an OVC core in a broken deck gets its own label; under Total, where they are one area, it reads BKN/LCA OVC. Specks of a cell or two get none.
• A thin line separates amount from band. An LCA label takes two lines, broken after the slash (OVC/ over LCA BKN), the band right of both. No colour square: the word gives the cover, the band the height. A HIGH label is grey, so cirrus recedes behind the cloud that limits a VFR flight.
• A label classifies the cover as drawn (two forecast hours blended to the minute, smoothed like the raster), so it cannot name a hole the map does not show.

Both use one smooth reconstruction of the model grid, so an edge is a smooth curve at the model’s resolution, not the observed edge of a cloud.

11.4 Precipitation

A GPU-rendered tint for the rate, with animated drops and flakes over it: the Precipitation row under Rain & storms (source Model), a surface quantity that ignores the altitude bar.

• The colour edges are the click popup’s words, printed in the key under the colours. Snow washes the colour toward white; sleet is a mix. Nothing is drawn below 0.05 mm/h.
• Strength follows confidence: a cell fades in between 20 and 50 % probability, full from 50 % up, but a rate of 1–3 mm/h fades in whatever the probability, so a heavy uncertain core shows at full weight while a broad low-confidence drizzle stays faint. Low confidence also greys the colour somewhat.
• Forecast showers and thunderstorms are floored to a visible band: a convective weather code is never blank.

WMO plates (the WMO symbols style) name an area like the icing, turbulence and CB labels: one white plate per area at its most interior point, repeated only about every 280 px, summing up its own area within that spacing. With the colour off they stay the same: like the SWC chart, they name areas and do not trace them.

• Nothing is marked under 0.1 mm/h or where the tint paints nothing, except freezing rain or drizzle.
• Freezing rain and drizzle always get their own red plate, with every combination of colour and symbols, at any painted rate, at least once per patch however small, never merged into a rain plate, and ahead of the freezing-level, cloud and ceiling labels for space: it is the one precipitation that ices the airframe, and magenta streaks among blue are easy to miss. Other plates give way to every label. With colour and symbols both off only these are drawn, and the key says so.
• The key shows only what is drawn: the rate scale while the colour is on, the chance row only for a model that publishes a probability, the rows of the symbol style in use.

Computed from Open-Meteo’s precipitation (mm water-equivalent per hour), snowfall (cm fresh snow per hour, ~10:1 ratio) and precipitation_probability on the grid. Snowfall over precipitation is a “snow fraction” that sets the rain↔snow colour and symbol mix per cell. The probability is an ensemble product paired with the model, not its own field: ICON-EU-EPS under Weather: Europe, none under Global (ECMWF publishes none). The popup names which it quotes; without one, the tint follows the rate alone.

11.5 Temperatures

A smooth GPU-rendered heatmap of air temperature on the standard meteorological scale: the Temperatures row under Air mass & warnings (source Model), at the bottom of the weather stack so the other overlays draw over it. Altitude-aware: the altitude bar appears while it is on. Temperatures — °C labels (off by default) prints decluttered values.

Level: Auto is temperature_2m; the rest the nearest pressure level: FL025 → 925 hPa, Low/FL050 → 850, Mid/FL100 → 700, FL140 → 600, High/FL180 → 500, FL240 → 400, FL300 → 300 hPa.

Computed from the shared weather grid of the cloud and precipitation layers (ICON-EU tiles under Weather: Europe, an 80×80 Open-Meteo grid over the view under Global), fetched once for all of them. A WebGL raster: the grid is a texture, the GPU does Mercator-correct bilinear sampling, and a 256-entry colour look-up texture from the named stops applies the exact ramp, smooth and anchored across zoom and pan with no per-frame CPU work. Switching level keeps the current frame until the new data arrives (no blank flash).

11.6 Fog

A GPU-rendered raster where surface visibility is forecast below 5 km: the Fog row under Cloud & visibility (source Model), surface-only, with no altitude selector. Four bands, classified in the shader, in distinct blue-grey tones with no blending, so edges are sharp. Use it for overnight valley-fog risk, freezing-fog corridors in winter, and a safe diversion when your destination is below CAT 1 minima.

Sub-zero BR is not FZFG: freezing mist at 1–5 km is an observation nuisance, not a hazard.

• One white plate per fog bank, as for precipitation, icing, turbulence and CB. Mist, fog and dense fog that touch (or lie within about 30 px) are one bank; the plate stands at its most interior point, repeating about every 280 px, the same with the colour off. Plates keep clear of aerodromes and other layers’ labels.
• Freezing fog always has its own plate, in all three modes (with its number after the mark in Visibility), never merged: fog that ices on contact is not for a labels choice or an “LCA” to hide. Its plates go first, and one near the screen edge is pulled in rather than dropped.
• A plate stands only where the raster paints (smoothed the same way), but says what the model’s own cells say, so a narrow freezing-fog band smoothed into mist still gets its FZFG plate and visibility.
• Hover a plate (mouse or trackpad), laid out as the precipitation hover: a bold title (Mist), one fact a line (Locally fog, Lowest visibility in this fog bank 400 m, Ices on contact for freezing fog), and, dimmed, the source (Model, or Model, corrected by live observations).
• Both choices are restored the next time the layer is on.

Computed from the model’s surface visibility (m) and temperature_2m (°C) in the shared grid of the Cloud cover, Precipitation and Temperatures layers (ECMWF under Global), each pixel put in exactly one band by the WebGL fragment shader. At Now the grid is blended with live FMI observations (FMI’s weather::simple AWS visibility and the visibility of the METARs the app holds for the view) by inverse-distance weighting within ~75 km of each, which pulls coastal fog banks the model misses (Russarö, Utö, etc.) into place. The observations fade out over the first 30 minutes of the time bar; forecast hours are model only.

11.6b Active-layer rail

A strip of chips along the bottom of the map, one for every layer that is on, each weather chip carrying its own colour ramp in miniature. It answers “what have I switched on” and “roughly what do these colours mean” without opening anything, and it replaced the Legend panel: that panel’s keys were moved behind the chips, not copied, so they stay live. Measured with five weather layers on, the old panel took 691 px of a 751 px desktop viewport and 752 px of a 375×812 phone, scrolling to 1,520 px; the rail costs about 28 px, 3–4 % of either screen.

1 2 3 4 5 6 7 8

• Every layer gets a chip: every weather layer, the four LLF layers, GPS Interference and Traffic (ADS-B), the three airspace layers (Terminal Airspaces, Special Use Airspaces, ACC Sectors), Airports, and the two navigation groups. The rule is whether the layer has something to explain or something to change, and every layer on the map has one or the other. The one map layer without a chip is the country boundaries: no key and no setting, so a chip would open an empty sheet.
• The navigation groups share seven layers between two chips, cut by flight rule rather than by kind. IFR: AMA grid, IFR points, airways, navaids. The area minimum altitude belongs here and not with the obstacles, because that is what it is: the ENR 6 enroute number that clears the quadrangle. VFR: obstacles, power lines, VFR reporting points. Obstacles are not VFR-only; both groups can be on at once, and are. A group’s chip appears when any member is on. In the Views window’s Layers tab the same grouping is one row under the Navigation heading, the members as tags you can flip one by one; the row’s own switch is a master, and switching a group back on restores the members that were on when you switched it off (all of them the first time).
• The sheet: its settings are built by the same function the Views window’s Layers tab uses, so the two can never offer different controls for one layer. Tap the chip again, tap the map, press Esc, press the sheet’s × or swipe it down to close. The Special Use Airspaces key (the R / D / P / TSA swatches and the three activation states) lives behind its chip like the rest.
• One switch, one place. A layer’s own options (symbol toggles, label toggles, styles) live only in its settings, reached from the chevron on its row in the Views window or from its chip. A layer’s key carries no switches; the ceiling’s CIG / VIS labels and the temperature’s °C labels are settings too, which is what lets them travel with a view.
• Swatches or names. By default the chips keep their colour swatches while the whole row fits, and show names only when it would not.
• On a phone the strip scrolls sideways, so it stays one row however many layers are on. The edge with more fades and a small ‹ / › appears on that side; press it and the strip scrolls about a screenful. The always-on chips sit at the end so overflow eats them first, never the weather layer you switched on a second ago.
• Minimising the strip. The strip is on permanently, and one round button folds it away. It sits in the bottom-left column directly under where the strip starts, the same size and shape as the Menu button beneath it, and steps Auto → Names only → Hidden → Auto; its icon shows the next step, and it skips Names only when the strip already shows names. The choice is remembered on this device. With nothing on there is no button either.

11.7 Icing

A GPU-rendered raster at the level or slab on the altitude bar, in the four ICAO intensities: the Icing row under Icing, source Model (its LLF and MET NO sources are the official low-level forecasts, Section 13). Use it for choosing a non-icing FL, deciding whether to file an alternate with non-icing approach options, and checking route icing seen in the airgram.

• Each band is one flat colour with a crisp edge, as turbulence is drawn. Blue because icing is the one hazard here that is purely about cold; it shares no hue with turbulence or convection.
• Icing being sparse, they grew the painted area only from about 3 % of a Nordic viewport to about 5 %.
• MOD / SEV labels (Icing — MOD / SEV labels, on by default) write the intensity in the key’s words, and SLD in violet for freezing rain / supercooled large drops. The printed weather overview keeps the SWC horseshoes (∪ / ∪∪).
• FL band labels (off by default) give where the icing is in the multi-level slabs (Total / Low / Mid / High), in the LLF layer’s badge: intensity on the left, the upper level over the lower to its right (the levels alone with MOD / SEV off). One label per area of the same reading, near its middle, repeated only on a large area.

• Outline and Off show moderate and worse only; trace and light get no edge or label, and the key says so.
• The line is the MOD label’s threshold, so line and label never disagree. A lone moderate or severe speck under about two model cells gets no edge (it would read as noise; the bands still paint it); freezing rain always does.
• Edges and labels ignore the weather-opacity slider.

Computed. Risk is non-zero only when both hold:

1. The temperature at the level is in the supercooled-water window: full risk at 0 … −12 °C, tapering to −24 °C as the cloud glaciates (below roughly −15 °C droplets increasingly freeze to ice crystals, which do not ice the airframe), and
2. Cloud cover at the level is ≥ 50% (visible moisture is needed for accretion).

11.8 Turbulence

A GPU-rendered raster at the chosen FL slab flagging clear-air turbulence (CAT) in the four FAA intensities: the Turbulence row under Wind & turbulence, source CAT (its LLF and MET NO sources are the official low-level forecasts, Section 13). Deliberately transparent: a layer you read the map through.

Each step is darker than the last, none is VFR green, and red-green colour-blind eyes still tell Moderate, Severe and Extreme apart.

• MOD / SEV / EXT labels (on by default; EXT in plum) and FL band labels (on by default: where the shear lives in multi-level slabs, upper over lower, right of the word).
• One label per area of the same strength: levels do not split an area but appear as ranges, tops above, bottoms below (080–100 over 050–060), from the part the label stands for, one value where they agree.
• A large area repeats its label only every few hundred pixels; a separate area gets its own. Extreme and severe go first; moderate gives way to a severe or extreme label close by (severe never to extreme).

Nothing below FL050. The layer starts at 850 hPa, about FL050. Below it the model’s shear measures the wind growing out of the friction layer, while the thresholds were made for clear air at jet level, and it is wrong more often than right there: it paints wide areas moderate or worse where the low-level forecasts have little, and misses a strong, well-mixed wind with little shear. So by default nothing below FL050 is drawn on the map or read in the popup, and nothing is ever hatched in the airgrams, named on the Brief tab or printed in the weather overview. FL025 draws nothing by default, and the key says why. Low-level turbulence is the forecasters’: the LLF Turbulence layer (Section 13, the Nordics), the GAMET and SIGMETs. On the Brief tab a leg wholly below FL050 reads not analysed below FL050, not a green “none”, and a leg above it says it was judged from FL050 up.

Showing the model below FL050 anyway. Turbulence (CAT) — below FL050, under the chevron or in Settings: Not shown (default) or Model wind shear (unverified), which paints under FL050 too, with the same shear, stability and boundary-layer damping: FL025 and Low from the surface, Auto the whole column, the Outline’s purple line from the surface, and the key says those colours are unverified. A choice of picture, not of verdict: only the map and its popup follow it. The Brief tab, both airgrams and everything printed (the briefing maps, which carry no key to say so, and the weather overview) stay at FL050, so a leg reads the same on every device and on paper. Part of a view; a view that does not name it shows nothing below FL050.

• The Outline is at the label’s severe threshold, so line and SEV/EXT label cannot disagree. A severe patch under about 18 km across gets no ring; its label still marks it.
• Outline and Off do not label light turbulence, and the key says so.

Computed. Vertical wind shear between neighbouring pressure levels from 850 hPa up, as closely as the model publishes them (50–100 hPa apart), so a thin shear layer is not averaged away. Pairs are rebuilt per view from the levels actually published: the Nordic model returns 950, 900, 800 and 750 hPa as null, and a phantom level would read as enormous shear. Wind, direction and temperature come through the shared grid; the field is a WebGL raster. Shear maps to the FAA scale:

Then refined, to flag where shear is likely to break into turbulence rather than every windy gradient:

11.8b Cloud tops — Model

Cloud tops is one row with two sources, one shown at a time: FMI (satellite observation, fine and current) and Model (this forecast, coarse but able to run forward). They answer the same question from opposite ends on one colour scale, so switching compares like with like. On Model, colour is how high the topmost deck reaches, in nine hard-edged steps (one per published level) on FMI’s cloud-top scale: dark magenta at the surface, pink at FL050, near-white at FL100, green and pale blue at FL140–FL180, then yellow, orange and red from FL240 up.

Labels (on by default; Cloud tops — FL band labels under the chevron) give the topmost deck’s top over its base (FL340 over FL180), in red when the top is above the service ceiling of the flight on the map, or of your default aircraft. That is the point of the mode: a climbing pilot asks “can I get on top”, not “what is the base”.

11.9 Convective Activity

One GPU-rendered overlay for everything convective, encoding two separate things in two channels: hue for how bad, form for whether it is happening.

The first two are on the layer’s key (Section 4.1.1). Weather forecast paints colours with no edge; SWC (Model) the edge with no colour.

Labels and anvils

OCNL over CB | ~340

• The SWC chart’s words: coverage, then CB (TCU for a weak cell), stacked on the left; the top in hundreds of feet on the right behind a thin line, as on the icing and turbulence badges. A mixed word (ISOL/OCNL) stays on one line, so every label is two lines high.
• Coverage in ICAO’s bands (ISOL under half, OCNL half to three quarters, FRQ more, ISOL/OCNL or OCNL/FRQ where it varies), counted in model cells, not cloud area: a model flags a whole 7 km cell and cannot say how much a CB fills. So the word is the share of cells passing the label’s test (deep convective cloud or a thunderstorm code) among the nine squares of the 80 km the label stands for, counting only squares holding a CB, as the chart draws its area round the CBs. Nothing countable: just CB.
• Strength (MOD, STRG, SEV) is the colour, not on the label. A SEV label is in the SEV ink; every other, TCU included, in the dark ink of the other weather labels.
• Neighbours share a label: storms within about 230 km that would print the same (word, CB or TCU, strength) get one, on the strongest on screen, its top a range (~120–280) when they differ by 4,000 ft or more, else the highest. A group spans at most about 400 km, so a shower field off the coast reads as a few labels, not one every 80 km. Each CB keeps its own anvil. The range is on one line because on the SWC two stacked numbers are top over base.
• The same at every zoom: which storms get a label is decided in kilometres (about 80 km to a cell), so zooming in reveals labels hidden by overlap without renumbering the rest (a storm entering the forecast area at the screen edge can still widen a range). The level is the highest top in the cell, so it does not wander.
• The top is rough, hence the tilde. It is the model’s convective cloud top, or, where that is missing or below about 3 km (a cell admitted on a thunderstorm code alone), an estimate from CAPE. Against the radar echo tops of 99 lightning-confirmed storms over the summers of 2025 and 2026, it did no better than one constant height and was often several thousand feet off: read FL250 versus FL350 storm, not a level to climb over. The airgram’s CB silhouettes and the printed overview mark base and top the same way (~FL330, base ~FL007).
• Deep enough to be a CB: a label only where the convective cloud is at least ~2 km thick (or, with no published base, tops above ~FL100), or a thunderstorm is forecast (WMO 95–99). Shallow convective cloud is left to the raster.
• The anvil above a CB label is the printed overview’s cumulonimbus mark: solid where a thunderstorm is forecast (WMO 95/96/99), hollow for a tower only; a TCU has none. With the labels off it stands alone, as the SWC marks a CB. A forecast: observed lightning is Lightning strikes (FMI).

Computed from Open-Meteo’s DWD ICON: cape (Convective Available Potential Energy, J/kg), convective_inhibition (CIN, J/kg), weather_code, convective_cloud_top / convective_cloud_base (the forecast cloud, for the “active” test and the top), and temperature_850hPa / temperature_500hPa / freezing_level_height for the lapse-rate cue. ICON specifically, the only layer insisting on a model: no other Open-Meteo source publishes convective cloud top, base and freezing level (MET Norway returns none of them). Its grid is about 7 km, and zooming in will not sharpen it. When the rest of the map comes from another model, the source line under the Clouds, Cloud tops and Precipitation keys names each model, its layers and grid size. A second source, best_match, was withdrawn: with no convective top and no thunderstorm codes it could not tell a fired cell, and its stand-in cloud-cover test flagged warm-front overcast as convection.

The field is anchored to latitude/longitude, so pan and zoom never move the patches over the ground.

The CAPE ranges (before CIN and floors) set the tier; the label’s top comes from the forecast convective cloud top wherever that is at least about 3 km, and the last column is only the rough range per tier.

11.10 MSL Pressure

A GPU-rendered pressure field on a diverging blue → white → red scale (deep blue low, white near the 1013 hPa standard, red high), thin isobars, and H / L letters with their core value at the centres. Use it for the synoptic picture: tight isobars mean strong wind, a closing “L” a deepening low.

• Settings (chevron on the MSL pressure row, or the chip), each part on its own: Colour (off by default), Isobars and H / L centres (on). Remembered, part of a view; a view saved with the old single choice (Colour, Isobars + H/L or Both) opens with the same parts on.
• Computed from pressure_msl on the shared model grid, a WebGL raster with a GPU colour look-up. Marching squares extract the isobars (4 hPa interval); a connected-component search finds the centres.

11.11 SIGMETs/Warnings

Issued (non-model) hazard polygons from two sources, pulled live and refreshed every ~5 minutes, following the time bar (Section 8).

• Outline = timing, the SUA convention (Section 10.3): solid active at the time on the bar, dashed activating later the same UTC day. Nothing else is drawn: expired entries, and those starting tomorrow or later, wait until the bar reaches their day. Scrub forward to see dashed turn solid and plan round an incoming warning.
• Hover: a severity pill over the headline. Click: the map popup (Section 7) lists every alert under the point with source, validity in UTC, headline, plain-English description, peak wind / probability, and the altitude band (SIGMETs only).

11.12 Nordic SWC

The forecasters’ Nordic Significant Weather Chart drawn on the map in place: scallops, fronts, jet axes, 0 °C boxes and every cloud line with its levels over the ground they describe, so you see which your route crosses. The Nordic SWC view (Section 14) or the Nordic SWC row under Air mass & warnings.

Computed: FMI / SMHI / DMI / MET Norway publish a vector PDF four times a day, valid SFC–FL450. The app’s server returns its ink as geometry, placed with the projection recovered from the sheet’s own graticule (polar stereographic, 15 E). Nothing is redrawn or interpreted. Cached for offline use with the other hazard charts (Section 24).

11.13 Euro WAFC

WAFC London’s fixed-time SIGWX chart for ICAO area EUR (FL100–FL450) on the map in place, as one object that scales with it, like the Nordic SWC (Section 11.12): CB areas with tops, icing and turbulence areas, jet axes with levels, the tropopause. The Euro WAFC view or the Euro WAFC row under Air mass & warnings.

XXX means below the chart’s lower limit, FL100. WAFC retires these picture charts in November 2028.

11.14 The Norwegian Low Level Forecast (MET NO)

The Nordic LLF (Section 13) covers Sweden, Denmark, Finland and Estonia and stops at the Norwegian and Latvian borders. Norway publishes its low-level forecast as map layers from the Norwegian Meteorological Institute; these five bring them in, and over Norway they are the only low-level product the app has. They are a MET NO source tag on five rows: Cloud cover and Visibility (Cloud & visibility), Turbulence (Wind & turbulence), Icing and Freezing level (Icing; the last shared with the model source, Section 11.15).

11.15 Freezing level (model)

The height of 0 °C as a field, in 1000 ft bands from the surface (blue) through green and yellow to orange-red at 10 000 ft, then magenta to pale lavender at 20 000 ft. The LLF section’s 0°C row and the airgram’s hover give it at a point; this answers where along my route the freezing level drops through my cruising altitude.

• A surface freezing level is drawn, not dropped: a column wholly below freezing reports zero, the leftmost band, the most operationally interesting value.
• The scale must reach 20 000 ft: across the ICON box on a September afternoon 62 % was above 10 000 ft (median 12 100, highest 17 700 ft); stopping at 10 000 painted two thirds of Europe one colour. Blue to red is MET NO’s own ramp, the same heights in both.

Limits: ICON only, the one Open-Meteo model with this field (MET Norway’s Nordic model returns nothing at every hour, measured), so nothing outside ICON’s box. At 7 km it is regional, not a valley freezing level, which matters in the mountains; MET NO is finer where it reaches. No extra download with Convective activity on (the same bundle of fields); alone it fetches the whole bundle for one field.

11.16 Flight category, and the two readings behind it

The layer long called Ceiling draws a flight category, VFR to LIFR, from a ceiling and a surface visibility, and those two are layers of their own: not only is it IFR but which of the two made it IFR. Three rows under Cloud & visibility, in this order:

• The steps are the category’s own (8, 5, 1.5 km; 3000, 1000, 600, 500 ft), so apart from the 3 km step, which only shades the IFR range, a colour change on a component is a category change above it. One grid, one derivation: the three cannot disagree.
• Inked one-sided: clear means not what limits you, ink means this is. A green wash over half of Europe would answer no question.
• Zoomed out, a cell shows the WORST beneath it, the lowest visibility and ceiling of its cells, as the category does; an average could read “12 km” on a cell painted IFR for a 2 km patch. Visibility is stored to 50 m, so a value on 8 km may lie a little either side.
• Saved views are unchanged: one that turned on Ceiling still draws the flight category (only the row heading is new) and never silently becomes the separate ceiling-height layer.

• The Outline follows the two readings rather than the category steps, generalised as a forecaster draws: traced at the model grid it zig-zagged at every cell, so it is smoothed by about one model cell and moves from the coloured cells by about that much.
• A patch, or a clear gap inside an area, under about 500 km² (some 22 km across) gets no line; IFR or LIFR is always inside one (fog over one field is still fog). The plates then stand only inside the line, at least one per area big enough.
• The chart draws its line outside mountain areas and marks obscuration separately; the model’s ceiling is above the ground under it, so this line runs over the fells too.

11.17 Tropopause

The tropopause as the Significant Weather chart prints it: boxes with a flight level (340) and pentagons at highs (H over the number) and lows (the number over L). Labels only, no colour. The Tropopause row under Wind & turbulence, and part of the SWC (Model) view (Section 14.1).

Why. Where the troposphere ends and temperature stops falling with height. Indirect but useful for a piston twin: CB tops seldom pass it, so a high tropopause lets convection grow tall; a low one marks cold air aloft (an upper low or trough, showers, icing higher than the surface suggests); and the jet and its CAT run where it steps down.

12. Radar, Satellite & Lightning

What the weather is doing now: radar, satellite and lightning, each an observation fetched live from its provider. Unlike the forecast layers (Section 11), with no connection their rows grey out instead of drawing nothing.

12.1 What it is

They have no menu of their own any more. They sit in the Layers tab of the Views window, on the rows that ask the same question as the forecasts:

• FMI is the Finnish Meteorological Institute (ilmailusaa.fi / openwms.fmi.fi). How far each layer reaches is in the table below.
• The Weather now view (Section 9, on the bar out of the box) turns on the FMI satellite with the radar, the CB / TCU cells and the last hour’s strikes over it in one tap. Weather radar in the view list is only the FMI radar and the strikes.

12.2 Available layers

All nine layers ship to every user.

12.3 Time control for observation layers

The time bar (Section 8) drives these layers. While observation layers are the only time-aware layers on (no forecast layer, and the route’s weather panel closed), it runs in observation mode:

Approximate data windows:

Turn on any forecast layer as well and the bar leaves observation mode: ‹ › step whole hours, the picker lists hours from 12 h back to 7 days ahead, and an observation layer whose window the bar has left shows its red pill.

12.4 Reading the colour palettes

Each layer has its own palette: the same colour means different things on the radar and on the lightning heat map. Ramps run from weakest to strongest.

Cross-checking a CB forecast: Radar / Radar (FMI) tells you how heavy the precipitation is, Storm tops how tall the cell is. Bright magenta radar at an FL300 storm top is a fully developed CB; the same return at FL080 is a stratiform-rain bullseye and far less hazardous.

12.5 How the satellite image is drawn

The satellite product is a photograph. While the sun is up nothing in it is transparent: clear ground is painted as solidly as cloud, so laid flat over the map it hides lakes, coastlines and airport labels everywhere, even where there is no weather.

The Satellite image setting, under the chevron on the Satellite image row in the Layers tab or on the layer’s chip, offers three ways to draw it. One setting covers both sources, FMI and EUMETSAT.

• At night the EUMETSAT image paints clear ground near-black rather than leaving it out, so its cut-down modes use a lower brightness threshold on the night side, blended into the daytime one through dawn and dusk by the sun’s height at each point. City lights are left out.
• The choice applies to the printed briefing too: a printed map page with a satellite image on is drawn as on screen.

13. The Nordic Low Level Forecast (LLF)

The LLF, a Nordic aviation-meteorology product served by the Finnish Meteorological Institute, draws polygons of aviation-significant conditions (vis < 8 km, ceiling < 2000 ft, icing, turbulence, CB/TCU), updated every ~30 minutes.

Which area a field is in comes from the product’s own published polygons. A field outside every area shows no LLF section, among them four Swedish mountain airfields near the Norwegian border (ESKS, ESNC, ESUE, ESUT). Bornholm is in Sweden’s southern area, as the product files it.

13.1 Sub-layers

Each sub-layer is the LLF source tag on a Layers-tab row. Outside the ten areas every one is simply empty.