The three models
ECMWF IFS is run by the European Centre for Medium-Range Weather Forecasts, an organisation funded by European states. Its Integrated Forecasting System is widely regarded as the most accurate global model for the medium range, three to ten days ahead. The version used here has a grid of about 25 km.
GFS is the Global Forecast System from the US National Oceanic and Atmospheric Administration. It runs out to 16 days, updates four times a day, and is freely available, which makes it the model behind a great many forecast apps.
ICON is the Icosahedral Nonhydrostatic model from Germany’s national weather service, the Deutscher Wetterdienst. Its global grid is about 13 km, and over Europe it nests a finer model, which helps in the Alps. It runs to about seven and a half days.
Which is best for snow?
None of them, all the time. ECMWF tends to have the edge on the big picture beyond three days. ICON’s finer grid over Europe helps with Alpine detail. GFS runs the furthest ahead. On any given storm, any of the three can be the one that gets it right, and the differences between them are usually larger than the difference between the best model and the truth.
That is why snowingplaces uses all three rather than picking a favourite. When they agree, the forecast is labelled Likely. When two of three show snow, Possible. The snowfall range runs from the lowest model to the highest, so the width of the range tells you how sure to be.
What all three have in common
They are global models on grids of 13 to 25 km. A grid box that size in the Alps contains a valley floor and a summit, so the model’s terrain is a smoothed average of the real thing. Our data source adjusts temperature to the height of each forecast point, which is why a resort’s village and top-lift forecasts differ, but snowfall on a single ridge or in a single bowl is beyond any global model. Local knowledge and the resort’s own report fill that gap.
Where the data comes from
All three models reach snowingplaces through Open-Meteo, which collects the raw model output from each agency and serves it in one format. The full method is on the how our forecasts work page.