Methodology

Likely Weather compares ten weather models: nine come through Open-Meteo and one from MET Norway (listed below). Each model publishes a new forecast four times a day, and a city shows the latest one available when it was last updated, for the next ten days.

The forecasts are grouped into 3-hour periods on the city’s local clock. Temperature, wind, pressure, humidity and cloud cover are the values at the start of each period; precipitation is the amount that falls during it.

Regional models cover Europe only, so a city elsewhere is compared across fewer models. MET Norway forecasts hour by hour for about the first two and a half days only; after that, the other models carry on.

The feels-like temperature is worked out for every model from its temperature, humidity, wind and sunshine (Steadman’s apparent temperature). MET Norway gives no sunshine, so its feels-like is the value in the shade. Wind gusts come from the Open-Meteo models only.

Past weather comes from Open-Meteo’s historical data: the ERA5 reanalysis back to 1940 and, for the most recent days, the ECMWF analysis. It is one value per hour, not a median of models.

The Android widget’s current temperature is the latest report from the nearest airport within 25 km, if it is at most 75 minutes old, from the US Aviation Weather Center. It is adjusted for the height between the airport and the city (6.5 °C per kilometre) and for how much the models expect the temperature to have changed since the report. Without such an airport, the widget shows Open-Meteo’s estimate of the current temperature.

• ECMWF IFS ECMWF
• ECMWF AIFS ECMWF
• GFS NOAA
• ICON-EU DWD · Europe only
• GEM ECCC
• UKMO Met Office
• ARPEGE Europe Météo-France · Europe only
• JMA GSM JMA
• CMA GRAPES CMA
• MET Norway MET Norway

The median is the middle value of all models that have a forecast for a period (with an even number of models, the average of the two middle values). The band around it runs from the lowest to the highest model. Wind direction takes a circular median, so 350° and 10° meet at north. The chance of rain is the share of models forecasting more than 0.2 mm in a 3-hour period.

For temperature, wind and pressure, a day’s disagreement is the average gap between the highest and the lowest model over the hours still ahead that day. For precipitation it is the gap between the models’ daily totals. Days follow the city’s local time. Thresholds:

• Temperature: agree under 2 °C, split from 4.5 °C
• Feels like: agree under 2 °C, split from 4.5 °C
• Wind speed: agree under 1.5 m/s, split from 4 m/s
• Wind gusts: agree under 2.5 m/s, split from 6 m/s
• Pressure: agree under 2.5 hPa, split from 6 hPa
• Precipitation: agree under 2 mm, split from 8 mm
• Humidity: agree under 10 %, split from 25 %
• Cloud cover: agree under 20 %, split from 50 %

A model’s value describes a grid square, not a street corner, and the grid’s height can differ from the city’s, which matters for temperature. Agreement is not accuracy: models that share data or physics can agree and still be wrong together. Likely Weather compares the models with each other, not with the weather that actually happened.