About wthr.technology

Observed

The Met Office rain radar for the UK and Ireland, refreshed automatically and animated over roughly the last hour and a quarter, over EUMETSAT (Meteosat) satellite imagery. The Area switch at the top of the Layers menu picks the radar and the satellite together: Europe gives the EUMETNET OPERA composite of national weather radars across Europe, and US gives the NOAA MRMS mosaic of radars across the lower 48 states (the last hour, about every 2 minutes) over NOAA's GOES-19 satellite (see below). Turn on METAR to see airfield reports: wind, temperature, dew point, weather and the aviation colour state (limits). Tap an airfield for its full report, its current TAF (forecast) in plain words, and a table of its last 24 hours of reports. Turn on lightning for UK strikes in the hour before the radar time, coloured by age, or radiosondes to see the weather balloon launch sites: tap one for a tephigram of its latest ascent. Older radar can be browsed from the Archive in the Layers menu.

Forecast

Forecast maps from several models. Tap the model name at the top of the map (or Model in the Layers menu) to choose one; the list is grouped by forecast centre and can be narrowed to UK, global or ensemble models:

• UKV (Met Office): the 2 km forecast for the UK and Ireland, about five days ahead.
• MOGREPS-UK (Met Office): an ensemble of 18 forecasts for the UK at about 2 km, up to five days ahead, with a new run every hour.
• Met Office Global: about 10 km, worldwide, up to seven days ahead.
• MOGREPS-G (Met Office): an ensemble of 36 global forecasts at about 20 km, up to ten days ahead.
• GFS (NOAA): about 28 km, worldwide, up to 16 days ahead.

Picking a UK model while the map shows somewhere else moves the map to the UK. Every model has rain with isobars (on UKV, Met Office Global and GFS the rain sits over the model's low cloud in grey, with medium cloud in a paler grey; the hourly UKV cloud is used for the nearest hour, and a switch in Layers turns it off), temperature with isotherms, and 10 m wind as arrows, barbs, streamlines or animated flow. The single-forecast models (UKV, Met Office Global and GFS) also have Precipitation total: the rain and snow (as water) that falls in the 1, 3, 12 or 24 hours up to the map time, or a custom number of hours, built from each model's own hourly, 3-hourly and 6-hourly totals (how); the time box says how many hours it covers. Tap the map for a chart of the running total since the run started. They also have Cloud: each model's own low, medium and high cloud cover, with low cloud in white, medium in blue and high as a faint lilac wash, more solid for more cover, and isobars on top. Switches under Show turn each level on or off, and the chart for a point shows all three. Tap the map for the values at a point. The Point info button, beside Layers, sets what else a tap opens: just the values (the default), a chart through the forecast, or a tephigram; the values label also has one-off Chart and Tephigram links.

An ensemble runs the same model many times from slightly different starts, so it shows how sure the forecast is. Choose how to show it: Members (one member at a time, with its own isobars; this is where an ensemble opens, as it loads quickest), Average (the mean of all the members), Percentile (from the 5th, a low-end case, to the 95th, a high-end one, with the 50th the median), Chance (the share of members with rain or snow, frost, warmth or strong wind, from a preset threshold or a custom one you type in, at least or below a value) or Spread (how much the members disagree). Tap the map and the values label shows how the members are spread at that point: bars for how many fall in each range (the PDF) and a line for the share up to each value (the CDF), with the 10%, median and 90% values. Turn on MSLP spaghetti (under the ensemble options in the Layers menu) for one isobar from every member over any layer, their mean in white dashes and a picked member in amber with all its isobars. The ensembles' charts are plumes: every member as a line, the 10–90% range shaded and the median in bold. MOGREPS-UK also has an ensemble tephigram, with every member's temperature and dew point, their 10–90% range and the median. The average, chance and spread are worked out in your browser, so the ensembles load a coarser grid than the single models; zoom in for more detail. How the ensemble statistics are worked out.

Scenarios: on either ensemble, tick group into scenarios under the ensemble options to sort the members into a few groups with a similar pattern, much like ECMWF's ensemble clusters. MOGREPS-G members can be grouped by the upper pattern (500 hPa height) or by pressure (MSLP); MOGREPS-UK by pressure. Choose the area (the map view, shown as a dashed box, or a fixed area), whether to compare them at the map time or over 24 or 48 hours around it (every 12 hours), and the number of groups (Auto picks it from how well the members separate). Each scenario has a colour and a share of the members. Pick one and the map (average, percentile, chance or spread), the values label, the plumes, the spaghetti and the MOGREPS-UK tephigram use only its members; its most typical member is a real forecast you can show on its own. Compare scenarios shows a small map for each, with red and blue where it is higher or lower than the average of all the members. Pin to this time keeps a grouping while you move through the forecast. The note under the scenarios says how clear the split is: ensembles often spread out rather than fall into tidy groups, so a weak split means the scenarios are only rough. MOGREPS-G mixes the latest run's 18 members with 18 from the run six hours before; if the groups mostly follow that split, the note says so. The grouping is worked out in your browser and needs a connection. How the scenarios are found.

IMPROVER models: two models in the Met Office group of the model picker come from the Met Office's IMPROVER post-processing system, which blends its own and ECMWF ensemble forecasts. IMPROVER spot shows the forecast sites on the map: their weather symbol for the hour before the map time, or their temperature, rain, snow, wind or gusts, thinned out so they don't crowd each other (zoom in for more; weather stations are shown first). IMPROVER gridded fills the map: temperature, feels-like temperature, rain, snow, wind (with median isobars), gusts, total cloud, visibility and UV, from a global grid of about 30 km, with rain and snow from the 2 km UK grid over the UK. In Layers, Show as picks a Percentile (5th to 95th: the 90th is the value only 1 in 10 outcomes is higher than) or a Chance of passing a threshold, where the data has one (gridded: rain, snow, gusts, visibility and UV; spot: rain, snow, wind, gusts and temperature, at the UK and nearby sites). A frame of the gridded model is about 1 MB per layer, so it loads more slowly than the other models. Neither model can be downloaded for offline use. On every other forecast model, the weather symbols switch in Layers puts the same site symbols over the map's layer for the map time (about 5 days ahead at UK sites, about 8 days elsewhere).

Spot forecasts: on the IMPROVER models, tap the map (in Time series mode on the gridded model) for the chart of the nearest forecast site, starting with the layer on the map. The chart drop-down switches between precipitation rate, wind speed, gusts, snowfall rate and temperature at 1.5 m (the Met Office models with a meteogram, and the ensembles, also offer these in Time series mode). They come from the Met Office's IMPROVER post-processing system, which blends its own and ECMWF ensemble forecasts and works them out for each site. The chart uses the forecast site nearest to where you tap (shown on the map with a dashed line to the point). Percentiles (pick any of 5, 10, 25, 50, 75, 90 and 95%; matching pairs are shaded) come from about 8,700 sites in the UK, Ireland and nearby Europe (hourly runs, about 5 days ahead) or, elsewhere, about 6,900 sites worldwide (a run every 6 hours, 8 to 14 days ahead). Chance gives the chance of going over thresholds you pick, at the UK and nearby sites. If there's no site near the point, the chart uses the other set and says so. Choose 48 hours (hourly), 5 days (3-hourly) or, for the global sites, 14 days (6-hourly). The chart starts from the map time. Along the top, icons show the Met Office's weather symbol for the site (sun, cloud, showers, rain, sleet, hail, snow, thunder, mist or fog, with a moon at night); hover or tap for its name. Where there isn't room for every hour, each icon stands for a block of hours (3, 6, 12 or 24) and shows its most common symbol. Symbols run to about 5 days at UK sites and about 8 days at global sites.

The Met Office Global model and GFS have the same maps, wind gusts, and a tephigram of the atmosphere above any point. The Plot drop-down under the tephigram switches it to a hodograph: the wind at each level from the surface up, coloured by layer, with the bulk shear from the surface to 850 and 500 hPa (also for the UKV and weather balloon ascents; not for ensembles). Switch on Normand's point (method) for the construction from the surface (cloud base if the air is lifted and the wet-bulb temperature), then drag the surface temperature and dew point to see where a parcel would reach free convection. A drop-down zooms the plot to the lower atmosphere, from the surface up to 300, 500, 700 or 850 hPa. The Met Office Global model also has wet bulb potential temperature at 850 hPa, with isobars. Both global models also have a heat index layer: how hot it feels in the shade, worked out from the 1.5 m (Met Office) or 2 m (GFS) temperature and humidity with the US National Weather Service's formula, in colours taken from the NWS Heat Index chart, from yellow at 27 °C (80 °F) to dark red, with thin lines at the NWS categories (formula and categories). Every single-forecast model (UKV, Met Office Global and GFS) has wind chill: how cold the wind makes it feel on exposed skin, from the temperature and the 10 m wind with the National Weather Service's wind chill formula. It is only shown where the formula applies (cold and windy), with thin lines where frostbite can set in within about 30, 10 and 5 minutes (formula and limits). Both models also show wind on pressure levels, from 1000 hPa near the ground up to 100 hPa above the jet stream: pick the level at the top right of the map. It is drawn as barbs (or arrows, streamlines or animated flow) over the speed in colour, with height contours for that level in decametres. Any tropical cyclones (hurricanes, typhoons and tropical storms) are shown with the Met Office's forecast track, coloured by strength, and a ring where each storm is at the map time; tap a track for its table.

GFS also has two ocean layers from NOAA's GEFS-Wave model (about 25 km, every 3 hours to 10 days, then every 6 hours to 16 days). Waves shows the significant wave height (the average height of the highest third of the waves, wind waves and swell together) in colour, with arrows pointing the way the waves are travelling, longer for bigger waves, and the GFS isobars on top. Swell shows the swell only: the model splits it into up to three swell trains coming from different directions, which are combined into one height (how), with the arrows following the biggest train. Waves raised by the local wind count as wind sea, not swell, so in a storm most of the height is wind sea. Tap the sea for the height, direction and period (the trains are listed when there is more than one); the chart shows the total, the swell and the wind sea through the run. Directions are given as where the waves come from, as for wind.

Warnings

Weather warnings in force now or coming up. The Area switch picks UK (the Met Office's warnings, with Met Éireann's for Ireland), Europe (the national weather services of the EUMETNET MeteoAlarm group, from Iceland to Israel) or the US (National Weather Service warnings, watches and advisories, in NWS colours). The When row shows what is in force now, for the rest of today, or on one of the next three days, and the Show chips pick one kind of warning. European warnings are coloured yellow (be aware), orange (be prepared) or red (take action). The list under the map groups them by country; tap a row to zoom to it, or tap an area on the map for the headline, what to do and the full text.

GOES-19 satellite (Observed, US area)

With the area set to US, the satellite under the radar is NOAA's GOES-19, which sits over the equator at 75°W and sees North and South America and the Atlantic. Each radar frame shows the newest satellite image taken at or before it. Turn the radar off and the satellite gets its own loop of up to 12 hours, with its own time bar. The full disc updates every 10 minutes; two storm sectors, boxes about 1000 km across that NOAA moves to follow the weather, update every minute. Choose infrared (cloud-top temperature, day and night), water vapour at three heights, shortwave infrared (fog and fires), visible, or the Airmass, Night fog and True colour mixes (true colour in the storm sectors only, as the full disc has no red band). Tap the map for the value there and a chart of it through the loop. The Met Office's tropical cyclone forecast tracks can be shown on top. Old links to the Satellite tab (?view=satellite) open this view with the radar off.

Routing

The Routing tab has two kinds: Cycle routing and Marine routing.

Cycle routing. Load a GPX route, or plan one by tapping the map (the line follows roads and paths), set when you leave and your speed, and see temperature, rain and wind every 30 minutes along the way, plus a chart of the weather along the height profile. The route can be coloured by temperature, rain, wind or grade (steepness). If the ride goes through sunset or sunrise, the app works out when and where you'll meet it and shades the stretches ridden in the dark (how route weather is worked out). It also checks the weather warnings (UK, Europe and the US): where the route crosses a warning that's in force when you'll be there, that stretch is marked on the map, the chart and the table, with a link to the warning on the Warnings tab. Warnings you'd pass through outside their times are listed too, greyed out. Routes in the UK and Ireland use the UKV model; anywhere else the Global model. More about route weather.

Marine routing. Load a passage plan as a GPX file, or plan one by tapping waypoints on the map (legs are straight, great-circle lines), set when you leave (in UTC or UK time) and your speed in knots, or pick a vessel type. Every 30 minutes along the way (hourly on passages over two days) it gives the 10 m wind in knots with its Beaufort force and gusts from NOAA's GFS model, and from NOAA's GEFS-Wave model the significant wave height, direction and period, the biggest swell, the wind sea and which way the sea meets the vessel (head, on the bow, beam, on the quarter, following), plus pressure, visibility and air temperature. Set your own wave and wind limits to see where a passage goes over them. Holds (at anchor, in port or hove-to) work like stops. The models' grid is about 25 km, so close to the coast and in harbours the figures are rough, and points the wave model sees as land are flagged. Not for navigation: always check official forecasts before you sail.

Export. The Export button (or ⬇ Export under the route summary) saves a picture of the route, fitted to the picture, with its colour key, the chart along the bottom and a box listing your settings, or a PDF (A4) with your settings, the forecast summary, the picture and the full table, ready to print or send. The PDF is made in your browser.

RST map

Forecast road surface temperature on Great Britain's roads, hour by hour from the Met Office UKV model (about 2 km), with ice risk. Zoomed out it shows motorways and A roads; B roads appear as you zoom in, then the smaller classified roads, and every public road from about town scale (private and service roads are left out). Road estimate starts from the model's own ground surface temperature, which is an average over each 2 km grid box (grass, fields, woods and towns), and adjusts it for tarmac: warmer than the ground on clear, still nights and in sunshine, and closer to the wet-bulb temperature in rain (the adjustments and ice rules). Model surface shows the model's ground temperature with no adjustment. Roads are outlined bright pink where ice is likely (at or below 0 °C and wet, snowy or frosty) and pale pink where it's possible. Tap a road for its readings. The adjustment uses rules of thumb from published road weather studies and hasn't been checked against road sensors. Bridges, shaded cuttings, valleys and town centres can differ from it by several degrees, and it doesn't know which roads have been gritted. It's a guide, not a substitute for official road weather forecasts.

3D

A box of forecast data from the ground up to a top you choose (50 hPa, about 20 km, down to 700 hPa, about 3 km; 100 hPa to start), drawn in 3D that you can turn, zoom and move. Pick a tropical storm from the list (the box follows it through the forecast, using the Met Office Global model's track) (with a box 8°, 12° or 20° across) or tap Choose an area on the map and draw your own box: drag its middle to move it, its corners and sides to make it any shape (for example long and thin along a front), and the handle above it to turn it (for example along a jet stream). A box can cover up to twice the area of a 30° square at the equator, with sides from 100 km to 60°; while you draw it shows the size, the grid spacing and roughly how much data each time will load. Bigger boxes get a coarser grid so the data stays about the same size, and phones use a coarser grid than laptops. Show wind speed, humidity, cloud (on GFS the cloud water and ice, on a log scale from 0.001 to 1 g/kg so thin ice cloud shows too; on the Met Office models the cloud cover in percent, which their data gives from the ground up to 6 km, marked by a dashed orange line), the warm core (each level's temperature compared with the average across the box; how the 3D data is built), vertical motion or temperature. Values above the "Volume shows from" setting glow through each other; the floor and the cut-away corner show every value, and tapping either gives the reading there. Animated wind adds particles that drift with the model's wind at every height, including rising and sinking air, coloured by speed (choose how many and how fast). Heights are stretched (×25 to start) so the layers can be seen. Met Office Global or GFS, or the Met Office UKV (about 2 km) for areas over and around the UK (it has no vertical motion, so Updraft is off and the particles move sideways only), any run and time. It's drawn by your own device's graphics chip (WebGL2, using three.js); nothing is drawn on a server.

Tabulated

Airfield reports in a table. The map shows the latest METAR station plots; tap Select stations and drag a box round the airfields you want (move or resize it with its handles). Below the map, each airfield gets a row with its colour state, report time, the raw METAR and the current TAF, or "No TAF" where there isn't one. Tap a row for both reports in plain words and to find the airfield on the map. The table refreshes every 10 minutes and shows up to 60 airfields.

Climate

Long-term averages at weather stations across Europe, from their daily records. The map shows the stations with a long enough record (gold for 100 years or more); tap one, pick it from the list under the map, or search for a place to open the nearest. You get the monthly mean maximum, minimum and mean temperatures, rain, rain days and sunshine for 1991–2020 (or 1961–1990, or the whole record), the highest and lowest temperatures recorded, how the last 12 months compare with the average, and every year's mean temperature as warming stripes. Values are as the national weather services supplied them, not adjusted for station moves or new instruments.

Annotate (Observed and Forecast) and Export

For briefings, tap ✏️ Annotate and draw on the map: cold, warm, occluded, stationary and upper fronts, troughs, squall lines, convergence lines, ridges, dry lines and jet axes, plain lines and arrows, H and L centres with their pressure, tropical storms, text labels, boxes, circles and areas (plain or scalloped). Tap points and the line is smoothed through them, or draw freehand; with an Apple Pencil or other pen, the pen draws and your finger moves the map. Front symbols go on the left of the way you draw (⇅ Flip swaps them). On the Forecast tab an H or L placed near one of the model's centres snaps onto it and takes its pressure, or add them all at once. A drawing can show at every time or only at the time on screen, so each forecast chart can have its own fronts (⧉ copies them to the next time). Save drawings as named briefings, download them as a file to share, or copy a link that opens the same map, time and drawing. Present fills the screen and adds a laser pointer. 📷 Export, on every tab except Tabulated, saves a picture (PNG) at a size you set; on Observed, Forecast, Warnings and 3D it can also make an animation of the times you choose as a GIF, MP4 or WebM. The time and the data credits go on every frame; Meteosat satellite pictures are left out. Drawings are kept in your browser only. Animations are made in your browser with gifenc, mp4-muxer and webm-muxer.

Offline

Before you lose signal, choose an area on the Offline tab's map, a model, run, layers and times, and download them. Switch the top of the page to Offline and the Forecast and Route tabs work from your downloads (the ensembles need a connection), on the site's own Offline base map. Downloads stay in your browser; you can also save them as a .wthr file (or straight into a folder in Chrome and Edge) and import that file later. Radar, satellite, airfield reports and the tephigram need a connection.