Data sources and methodology
Every number on this site comes from a named source, under a licence that allows it, and every sentence about the long range is written from those numbers by fixed rules. This page lists both. We never invent observations or forecast values.
Sources
| Used for | Source | Licence and attribution | Updates |
|---|---|---|---|
| Forecasts: current, hourly (72 h) and daily (14 days) | Open-Meteo, blending national weather service models (including the Met Office UK model, ECMWF, DWD ICON and others) for each point | CC BY 4.0; data from the UK Met Office is CC BY-SA 4.0 | Hourly |
| Confidence, runs that bring rain, plume (days 1 to 15) | ECMWF IFS ensemble, 0.25°, 51 runs, via Open-Meteo | CC BY 4.0 | Every 6 hours |
| Six week outlook | ECMWF EC46 extended range, weekly anomalies against the model's own climate, via Open-Meteo | CC BY 4.0 | Daily |
| Months ahead | ECMWF SEAS5 seasonal forecast, monthly anomalies, via Open-Meteo | CC BY 4.0 | Monthly, on the 5th |
| Climate averages, 1991 to 2020 | Copernicus ERA5 / ERA5-Land reanalysis, via the Open-Meteo historical API, computed once by us | Generated using Copernicus Climate Change Service information | Fixed |
| Air quality, pollen, UV | Copernicus Atmosphere Monitoring Service (CAMS) European model, via Open-Meteo | Generated using Copernicus Atmosphere Monitoring Service information | Hourly |
| Waves and sea temperature | Open-Meteo marine API (national wave models) | CC BY 4.0 | Every 3 hours on our side |
| Weather warnings | Met Office warnings RSS feeds, shown unedited with a link to the original | Met Office free services terms; attribution | Every 5 minutes |
| Flood warnings and alerts (England) | Environment Agency real-time flood-monitoring API (Beta) | Open Government Licence v3.0 | Every 15 minutes |
| Map wind, temperature, cloud, pressure and rain fields | NOAA GFS 0.25°, downloaded from NOMADS and decoded on our server | US public domain; no endorsement implied | Every 6 hours |
| Rain radar (last 2 hours) | RainViewer composite | RainViewer terms (free for personal and educational use); attribution | About every 10 minutes |
| Satellite images | NASA Global Imagery Browse Services (GIBS): VIIRS (NOAA-20) and MODIS (Terra) true colour | Public domain; NASA does not endorse this site | Daily |
| Base map | OpenFreeMap tiles from OpenStreetMap data | © OpenStreetMap contributors (ODbL) | |
| Place search | Open-Meteo geocoding, based on GeoNames | CC BY 4.0 | |
| Sunrise and sunset | Calculated by us from the NOAA solar position equations |
This uses Environment Agency flood and river level data from the real-time data API (Beta). Contains Met Office data. Weather data by Open-Meteo.com. Generated using Copernicus Climate Change Service information and Copernicus Atmosphere Monitoring Service information.
Forecast, outlook, climate, observation
Forecast: a model’s prediction of the weather at a place and time. Everything labelled “now” is the model’s analysis for this hour. No thermometer was read.
Outlook: beyond two weeks, a statement about whether a week or month leans away from normal. Never a daily forecast.
Climate: the 1991 to 2020 average for the place and time of year, from the ERA5 reanalysis grid. Reanalysis values smooth hills and coasts and can differ by a degree or so, or by a noticeable share of rainfall, from station averages published elsewhere.
Observation: a measured value. We do not currently show station observations.
Our rules, in full
Confidence (days 1 to 15)
For each day we take the daytime high from all 51 ECMWF runs and the share of runs with at least 1 mm of rain. The spread is the gap between the 10th and 90th percentile of the highs. Rain agreement is the larger of the wet share and the dry share.
- High: spread of 3°C or less and rain agreement of 80% or more.
- Low: spread of more than 6°C, or rain agreement below 60%.
- Medium: everything in between.
Leanings (weeks and months ahead)
- Temperature against the model’s own climate: within ±0.5°C is “close to normal”; 0.5 to 1.5°C “a little warmer/milder” or “a little colder”; beyond 1.5°C “warmer/milder” or “colder than normal”.
- Rainfall against the normal for the period: within ±10% close to normal; 10 to 25% “a little wetter/drier”; beyond 25% “wetter/drier than normal”.
Words in daily forecasts
A day is called wet with 1 mm or more, or with a 60% chance and at least 0.3 mm. Gusts of 40 mph or more are called gales possible. “Good for” suggestions use fixed thresholds of temperature, rain, gusts and UV. The same numbers always give the same words.
Location pages
Eleven cities and the four nations have full pages with local content. Any other UK place found through the search gets a live forecast page that is not indexed by search engines, until we can add something specific to it.
What we do not offer, and why
- Lightning: we have not found a free lightning source whose terms allow republishing on a website.
- Tides: official UK tide predictions are a licensed product; we link to them rather than copy them.
- Live satellite loops: geostationary imagery we could not confirm we may republish. We show daily NASA true-colour images instead and say so.
- Radar nowcasting: our radar source shows the last two hours only.
- Flood warnings outside England: we link to SEPA, Natural Resources Wales and NI Direct rather than show a partial copy.
Questions about any of this: contact us.