User Manual — Weather & Airport Information for Pilots
This is a free, browser-based weather and airport information tool for general-aviation pilots. It puts every significant airport worldwide (over 22,000 of them) on one map and overlays it with a complete suite of aviation weather forecast products — current conditions, multi-day forecasts, fog, icing, turbulence, and convection — so you can answer the questions that matter before a flight: Is the weather flyable? Where? When?
The app 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 for basic map content, full-screen on mobile).
What you can do:
The main screen is intentionally clean. Here is every control you will see and what it does:
| Where | Control | What it does |
|---|---|---|
| Top-left | Search bar | Find an airport by ICAO code, IATA code, or name (Section 4) |
| Top-left, below zoom | ◉ Locate | Show your current GPS position on the map; tap again to stop tracking |
| Top-right | ⛅ Weather forecast | Forecast layers: winds, clouds, precip, fog, icing, etc. (Section 10) |
| Top-right | SWC | Significant Weather Charts (Section 12) |
| Bottom-right | ↗ Draw airgram line | Draw a route on the map → vertical weather cross-section (Section 11) |
| Top edge (when needed) | Time bar | Past 12 h ↔ +7 day forecast scrubber (Section 8) |
| Top-right (when needed) | Altitude bar | Pick the level for layers that vary with altitude (Section 9) |
That's the entire UI. The map fills the rest of the screen.
Smaller airports become visible as you zoom in — large airports are visible globally, medium ones from zoom 5, small ones from zoom 7.
Click the search bar at the top-left and type at least two characters. Matches appear as a dropdown. You can search by:
EFHKHELHelsinkiPick a result and the map flies to the airport and opens its popup automatically.
| Type | Default colour | Visible from |
|---|---|---|
| Large airport | Red | Always |
| Medium airport | Blue | Zoom ≥ 5 |
| Small airport | Green | Zoom ≥ 7 |
Whenever a current METAR is available, the dot is replaced by a larger category badge with a single letter inside:
| Letter | Category | Colour | Ceiling | Visibility |
|---|---|---|---|---|
| V | VFR | Green | > 3,000 ft | AND > 8 km |
| M | MVFR | Blue | 1,000–3,000 ft | OR 5–8 km |
| B | BIR | Orange | 600–999 ft | OR 1.5–5 km |
| I | IFR | Red | 500–599 ft | (ceiling-only trigger) |
| L | LIFR | Purple | < 500 ft | OR < 1.5 km |
The worst-case rule applies: whichever value is in the lower category wins. METARs refresh automatically every five minutes.
If the METAR contains a fog/mist code, a small coloured tag appears under the airport identifier:
| Tag | METAR code | Meaning | Colour |
|---|---|---|---|
BR | BR | Mist (visibility 1–5 km) | Light grey |
FG | FG | Fog (visibility < 1 km) | Mid grey |
FZFG | FZFG | Freezing fog (T ≤ 0 °C) | Purple |
Click any airport marker. The popup opens centred on screen and shows:
Just below the codes you see the current METAR rendered as colour-coded chips:
| Chip | Example | What it shows |
|---|---|---|
| Category | VFR / MVFR / BIR / IFR / LIFR | Same colour code as the marker |
| Wind | Wind 240°/12kt G18 | Direction in degrees, speed and gusts in knots |
| Visibility | Vis 6.0km | Surface visibility in km (or "10+km" for unlimited) |
| Ceiling | Ceil 1200ft or CLR | Lowest BKN/OVC layer above field |
| Weather | -RA BR | Decoded weather phenomena (Section 14.2) |
| Temp | 8°C/5°C | Temperature / dewpoint |
| QNH | QNH 1013 | Sea-level pressure setting |
Below the chips you also see the raw METAR string — useful for cross-checking against another source.
Two warning badges may appear next to the category chip:
Below the METAR there is a TAF (Terminal Aerodrome Forecast) panel covering the next 12 hours, rendered as a visual timeline:
The same compact six-period forecast described in Section 7 is also embedded under the TAF. It uses the airport's coordinates and gives a longer outlook (up to 72 h) than the TAF.
An icing badge appears whenever any of these is true:
FZRA, FZDZ, FZFG, …)This is a deliberately permissive trigger — icing certificates require margin, and the cost of a false negative is far higher than a false positive.
Click an empty spot on the map (anywhere that is not an airport) to open the weather panel for that point. The panel is centred on the click and shows:
Big temperature, current weather (icon + text e.g. "⛅ Overcast"), and an AMA chip showing the local Absolute Minimum Altitude (terrain reference; see Section 14.4).
Inline pills (each with a hover tooltip) give the rest of the picture: wind, visibility, cloud cover (highest tier), estimated cloud base, QNH, RH, dewpoint, and the model freezing level. Hover any pill for a one-line plain-English explanation.
The bottom strip splits the next 48 hours into six daily slots (boundaries are local time):
| Label | Local hours |
|---|---|
| Day | 06 – 14 |
| Eve (Evening) | 14 – 22 |
| Nt (Night) | 22 – 06 next day |
The first cell is the next period after the current one (so opening the panel mid-afternoon shows Eve first, then Nt, Day, Eve, Nt, Day across two days). Each cell shows: weekday, period, an icon picked from the worst weather code in that period, the period maximum temperature, and the wind on the 8-point compass (e.g. NW 12) at the period's midpoint. Hovering a cell gives the full English description ("Friday Day · Light rain showers · 4 to 17 °C · wind 283° (W) / 5 kt").
Whenever a forecast layer is on (or you have an airgram open), a time bar appears at the top of the map. It controls all forecast overlays simultaneously, so you can sweep through "what does Friday morning look like over the Baltic?" in seconds.
| Button | Action |
|---|---|
| « | Jump 3 hours back |
| ‹ | Step 15 min back |
| label (centre) | Current offset (e.g. +3 h) and the absolute date / Zulu time |
| › | Step 15 min forward |
| » | Jump 3 hours forward |
| ▶ | Auto-play through the timeline (animated loop) |
| Now | Reset to "Now" (offset 0) |
The range is approximately −12 h ↔ +168 h (7 days). Past observations are limited by the source (e.g. radar nowcasts only publish a recent window).
Some forecast layers (Clouds, Icing, Turbulence, Winds, Precipitation, Thunderstorms, CB/TS, MSL Pressure) are inherently three-dimensional. A shared altitude bar appears in the top-right whenever you switch on a layer that needs one. Picking a level applies it to every active 3-D layer at once, which keeps cross-comparisons honest.
| Key | Roughly equivalent to | Pressure level |
|---|---|---|
| Total | Vertically integrated — the «public-forecast» view | — |
| Low | Surface – FL100 | 1000–700 hPa |
| Mid | FL100 – FL200 | 700–500 hPa |
| High | FL200 and up | 500–450 hPa |
| FL050 | ~5,000 ft | 850 hPa |
| FL100 | ~10,000 ft | 700 hPa |
| FL140 | ~14,000 ft | 600 hPa |
| FL180 | ~18,000 ft | 500 hPa |
| FL240 | ~24,000 ft | 450 hPa |
Click the cloud-and-sun icon (top-right) to open the forecast menu. You can have several layers on at once. Every layer in this menu is computed from Open-Meteo model data unless noted, and every layer responds to the time bar (Section 8) and the altitude bar (Section 9, where applicable).
The legend panel at the bottom-right shows colour scales and on-screen tweaks for each active layer.
What you see: Animated particles streaming across the map at the chosen flight level. Particles flow in the wind direction; their density gives a feel for speed; speed is colour-coded (cool = light, warm = strong).
How it's computed: The forecast model's u and v wind components at the selected pressure level are sampled on a viewport-fitted grid. Particles are advected each frame using bilinear interpolation, with random respawn to keep the field "alive".
Use it for: Picking the most efficient cruise level, spotting frontal shear, judging crosswind for an airport.
What you see: Soft cumulus-style cloud patches whose density matches forecast cloud cover percentage. Optional letter labels (CLR / FEW / SCT / BKN / OVC) are off by default.
How it's computed:
cloud_cover_low/mid/high directly.cloud_cover_<hPa>hPa at the matching pressure level.The renderer draws discrete "puffs" up to ~85% coverage and switches to continuous fBm noise at OVC, so the visual reads as real clouds rather than a heatmap.
Use it for: Quick "is there a hole?" assessment, ceiling height awareness, comparing cloud cover at different cruise levels.
What you see: Tinted areas with rain drops or snowflakes overlaid. Colour ramps from light blue (drizzle) through green and yellow to red (heavy rain); snow uses a separate white-to-magenta ramp; sleet appears as a lilac mix.
How it's computed: Open-Meteo's precipitation (mm water-equivalent per hour) and snowfall (cm fresh snow per hour, ~10:1 ratio) are sampled on the grid. The ratio of snowfall to precipitation gives a "snow fraction" which controls the rain↔snow colour and symbol mix per cell.
| Rain (mm/h) | Tag | Snow (cm/h) |
|---|---|---|
| 0.1 | Trace | 0.1 |
| 1 | Light | 1 |
| 3 | Moderate | 3 |
| 8 | Heavy | 8 |
| 16 | Very heavy | 16 |
| 40+ | Extreme | 40+ |
What you see: Tinted areas where surface visibility is forecast to drop below 5 km. Four severity bands match the airport-marker fog badges:
| Band | Visibility | Tint |
|---|---|---|
| BR (Mist) | 1 – 5 km | Light yellow |
| FG (Fog) | 200 m – 1 km | Orange |
| DENSE | < 200 m | Red |
| FZFG (Freezing fog) | any fog with T ≤ 0 °C | Purple |
How it's computed: Surface visibility (m) and temperature_2m (°C) are sampled on the grid. Visibility maps directly to BR/FG/DENSE; if temperature is at or below 0 °C and severity is FG or worse, the cell is upgraded to FZFG (purple) regardless of visibility band — freezing fog is treated as the worst case because of its rapid airframe-icing potential.
Use it for: Spotting valley-fog risk overnight, identifying freezing-fog corridors in winter, picking a safe diversion when your destination is below CAT 1 minima.
What you see: Yellow / orange / red / magenta tint at the chosen pressure level, indicating Light / Moderate / Heavy / Severe icing risk. Optional horseshoe pictograms (∪ for moderate, ∪∪ for severe) can be enabled in the legend.
How it's computed: Risk is non-zero only when:
A relative-humidity boost increases severity at high RH. The model draws from a slab of pressure levels — "Total" takes the maximum risk through the column; "Low / Mid / High" sample the corresponding slabs; FL050…FL240 sample one level each. A 3×3 averaging pass smooths single-cell hot spots.
Use it for: Choosing a non-icing FL, knowing whether to file an alternate with non-icing approach options, validating route icing seen in the airgram.
What you see: Diagonal-stripe shading in the same yellow→magenta scale as Icing, on the chosen FL slab.
How it's computed: Vertical wind shear is computed between adjacent pressure levels (e.g. between 700 and 850 hPa). The resulting shear in knots per 1,000 ft is mapped to the FAA's standard turbulence scale:
| Shear (kt / 1,000 ft) | Severity |
|---|---|
| < 4 | Light |
| 4 – 7 | Moderate |
| 7 – 10 | Heavy |
| > 10 | Severe |
Edges are alpha-faded with diagonal stripes so the layer reads as "rough air ahead", not a hard polygon.
What you see: Lightning-bolt symbols in cells where convective parameters cross thresholds. Number of bolts grows with severity.
How it's computed: Open-Meteo's cape (Convective Available Potential Energy, J/kg) drives the symbol density. Above ~300 J/kg is shown; thresholds 1000 and 2000 trigger the second and third bolt respectively.
What you see: Scalloped outline polygons in the SWC style, nested by severity, with WEAK / MOD / STRG / SEV labels.
How it's computed: A two-axis classification using CAPE and Lifted Index (LI):
| Severity | CAPE (J/kg) | LI (°C) |
|---|---|---|
| WEAK | 400 – 800 | −1 to −3 |
| MOD | 800 – 1500 | −3 to −5 |
| STRG | 1500 – 2500 | −5 to −7 |
| SEV | > 2500 | < −7 |
The cell takes the higher (more severe) of the two indices — the more pessimistic reading.
What you see: Isobars (constant-pressure contours) in hPa, with H/L letters at local extrema. Standard meteorological black-line presentation.
How it's computed: Open-Meteo's pressure_msl field is sampled on the grid. A marching-squares pass extracts contour lines at the chosen interval (default 4 hPa).
Use it for: Reading the synoptic situation — tightly spaced isobars mean strong wind, a closing "L" pattern means a deepening low.
What you see: Polygon outlines of currently active SIGMET areas (significant meteorological information — severe turbulence, severe icing, thunderstorms, volcanic ash, etc.). Click a polygon for the issuing FIR, validity, phenomenon, and altitude band.
How it's computed: This is not model-derived — SIGMETs are issued by national MET offices and pulled live from the NOAA Aviation Weather Center international SIGMET feed.
What you see: Up to 10 Nordic forecast areas (Finland, Sweden, Denmark, Estonia) with overlay zones and a forecast-period stepper. Click a zone for: flight category, visibility & cloud-base ranges, present weather, icing layers, freezing level, cloud tops, wind barbs.
How it's computed: National MET offices publish LLF; the app renders the structured XML/JSON feed.
An airgram is a vertical cross-section of the atmosphere: time and distance run along the X axis, altitude up the Y axis. It is the fastest way to spot icing, cloud, and turbulence layers along a planned route.
| Element | What it looks like | Meaning |
|---|---|---|
| Background colours | Blue → green → yellow → red gradient | Temperature at that altitude / time |
| Grey shading | Translucent fill | Cloud cover — opacity matches cloud % |
| Blue hatching | Diagonal stripes | Icing risk (T window + moisture) |
| Orange diagonal stripes | Translucent stripes | Turbulence (wind-shear severity) |
| Cyan dashed line | Horizontal line | Freezing level (0 °C isotherm) |
| White wind barbs | Standard barb glyphs | Wind every 2 h at each FL (Section 13) |
Hover the chart to read precise values (FL, time, T, wind, cloud cover, RH). The X axis can be set to either distance along the leg, or wall-clock time using the FL and Flight time inputs in the panel toolbar — useful for "what does the weather look like 1 h 30 min into the flight?"
Click the × in the panel header. The drawn line is removed automatically, the airgram-line button returns to its idle state.
The SWC button (top-right) opens a small panel with three tabs:
| Tab | Source | Best for |
|---|---|---|
| Finland | ilmailusaa.fi (PDF link too) | Detailed Finnish low-level SIGWX |
| Nordic | MET Norway | Nordic-region overview |
| Europe | WAFC London EUR SIGWX | European mid-level chart, ICAO standard |
SWCs are the official aviation-meteorology summary — jet streams, fronts, CB tops, icing/turbulence zones — and remain the gold standard for go/no-go decisions on longer flights.
Wind barbs follow standard meteorological conventions. The staff points into the wind direction — a barb pointing north means wind from the south. Speed is encoded as additive flags on the staff:
Wind speed is rounded to the nearest 5 knots. Barbs are additive: a pennant + two full barbs + one half barb = 75 kt.
| Cat | Letter | Colour | Ceiling | Visibility | What it implies |
|---|---|---|---|---|---|
| VFR | V | Green | > 3,000 ft | > 8 km | Comfortable VFR |
| MVFR | M | Blue | 1,000–3,000 ft | 5–8 km | Marginal VFR — experienced VFR pilots only |
| BIR | B | Orange | 600–999 ft | 1.5–5 km | Below IFR base — instrument approach territory |
| IFR | I | Red | 500–599 ft | — | Standard IFR conditions |
| LIFR | L | Purple | < 500 ft | < 1.5 km | Low IFR — CAT II/III approaches |
| Code | Meaning | Code | Meaning |
|---|---|---|---|
| RA | Rain | BR | Mist |
| SN | Snow | FG | Fog |
| DZ | Drizzle | HZ | Haze |
| PL | Ice pellets | FU | Smoke |
| SG | Snow grains | DU | Dust |
| GR | Hail | SA | Sand |
| GS | Small hail | SQ | Squall |
| TS | Thunderstorm | FC | Funnel cloud |
| FZ | Freezing | SS | Sandstorm |
| SH | Shower | DS | Duststorm |
| BL | Blowing | VA | Volcanic ash |
Modifiers stack: +SHRA = heavy rain shower; -FZDZ = light freezing drizzle; VCFG = fog in vicinity.
| Code | Coverage | Oktas | Forms a ceiling? |
|---|---|---|---|
| FEW | Few | 1–2/8 | No |
| SCT | Scattered | 3–4/8 | No |
| BKN | Broken | 5–7/8 | Yes |
| OVC | Overcast | 8/8 | Yes |
| VV | Vertical visibility | — | Yes (special: in fog/precip) |
| Measurement | Unit | Notes |
|---|---|---|
| Wind speed | Knots (kt) | 1 m/s = 1.944 kt |
| Visibility (Europe) | Metres | 9999 = 10+ km |
| Visibility (US) | Statute miles | 1 SM = 1,609 m |
| Ceiling / Altitude | Feet (ft) | 1 ft = 0.3048 m |
| Temperature | °C | "M" prefix in METAR = negative (M05 = −5 °C) |
| QNH (Europe) | hPa | "Q" prefix (Q1013) |
| QNH (US) | inHg | "A" prefix (A2992 = 29.92 inHg) |
| Distance | Nautical miles (nm) | 1 nm = 1,852 m |
| Layer / feature | Source |
|---|---|
| Airport database (~22,000 airports worldwide) | OurAirports — static build (PDDL public-domain) |
| METAR | Aviation Weather (US) & Autorouter (EU pass-through) |
| TAF | aviationweather.gov |
| Click-anywhere weather, six-period forecast | Open-Meteo (HARMONIE-AROME / ECMWF / GFS blend) |
| Winds, Clouds, Precip, Fog, Icing, Turb, TS, CB/TS, MSL Pressure | Open-Meteo pressure-level fields |
| SIGMETs (international) | NOAA Aviation Weather Center isigmet feed |
| LLF (Low Level Forecast) | ilmailusaa.fi (FMI) |
| SWC | FMI, MET Norway, WAFC London |
European Airports Map — User Manual
For pilots, by pilots · Updated April 2026