How we calculate historical snowfall — Methodology

STEP 1

Thirty winters of climate data

We start with ERA5, the global climate reanalysis from the European Centre for Medium-Range Weather Forecasts. It gives a complete daily snowfall record for every resort, but its 25km grid usually underestimates mountain snow.

STEP 2

Checked against mountain stations

We compare it with the nearest government mountain station, run by weather services and avalanche institutes with no stake in how good the skiing looks. We only compare days when both have a reading.

STEP 3

A cautious correction

Stations usually record more snow than the model. We close part of that gap, not all of it, so the figure fits the whole resort, not just the station's spot. Our figures are conservative.

EXAMPLE: LES ARCS

Les Arcs' own Météo-France station records about 13% more snow than the model. We add about 6%, giving a 30-winter average of about 550cm.

GOOD TO KNOW

Natural snowfall only, no snowmaking.
Snowfall, not snow depth on the ground.
A resort-level estimate, not a base or summit reading.
Often lower than resort-reported totals, which are usually measured high up.
A guide for comparing resorts, not exact to the centimetre.
Historical, not a forecast. Always check the mountain forecast before you travel.

RELIABILITY SCORE

A score of 21/30 means at least 350cm of snowfall in 21 of the last 30 winters, roughly 7 years in 10. Strong seasons reach 450cm, exceptional ones 550cm.

Station networks by country

Country	Station network
France	Météo-France Nivose, automated high-altitude snow stations. Each resort uses its nearest suitable station.
Switzerland	SLF (WSL Institute for Snow and Avalanche Research) snow study plots.
Austria	GeoSphere Austria daily mountain stations. Summit stations are preferred over valley stations where both exist.
Italy	Four regional networks: Bolzano, Aosta Valley, Trento and Lombardia. A few Piemonte resorts use a national figure while we secure station data.
Spain and Andorra	Meteocat XEMA high-mountain stations, using daily snow-depth records. Western Aragon and Sierra Nevada use a regional figure.
Scotland	Met Office MIDAS record at Cairngorm. Other Scottish resorts share a regional figure from it.

Known limitations

These figures are a strong guide to how snowy a resort's winters are, not a precise measurement. The main limits:

Station heights vary. Some stations sit high on the mountain, others nearer the village. Part of the gap between two resorts can reflect where their stations sit, so compare resorts as a guide, not to the centimetre.
Networks measure differently. Automated posts and hand-read snow plots record fresh snow in different ways. Comparisons across borders carry more uncertainty than comparisons within one country.
Very local snow is smoothed out. The model can't see wind-loaded slopes or snow pockets on individual faces.

Data sources and attribution

CHAMPOW's figures are our own analysis. They are not official statistics from any of the providers below.

Data	Source and licence
Modelled snowfall	ERA5 (ECMWF/Copernicus Climate Change Service), via Open-Meteo · CC BY 4.0
France	Météo-France, Nivose mountain network · Licence Ouverte 2.0
Switzerland	WSL Institute for Snow and Avalanche Research SLF · CC BY 4.0
Austria	GeoSphere Austria open data hub · CC0
Italy	Bolzano Province, Aosta Valley, Trentino and Lombardia ARPA regional networks
Catalonia and Andorra	Meteocat XEMA high-mountain network
Scotland	Met Office MIDAS

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