Methods & data
Forecasts with uncertainty in view.
What the snowfall range means
The headline range spans the 25th to 75th percentiles of the forecast distribution. The wider 10th to 90th percentile range and threshold probabilities provide more context.
Forecasts labeled provisional have not yet demonstrated reliable probability coverage against local observations. The range describes the model-based distribution; it is not a guarantee that half of observed outcomes will fall inside it.
Daily and storm totals are calculated from complete forecast trajectories before taking percentiles. Adding the lower or upper bounds from several periods would give a different, misleading result.
Snow is more than a temperature threshold
Snowfield uses atmospheric profiles to estimate snow ratio, melting, precipitation phase, and snow level. The physical method combines a published Cobb-style snow-ratio calculation, a wet-bulb melting correction, and revised Bourgouin phase diagnostics. A Kuchera fallback is labeled when cloud and ascent information is unavailable.
Precipitation-type probabilities can overlap in mixed weather. They are not treated as fractions of the precipitation mass. Missing model data stays missing.
References: NOAA snow-ratio documentation, Birk et al., revised Bourgouin method, and snow-ratio verification and melting correction.
Models and native resolution
Initial providers include ECMWF IFS and AIFS, their ensembles, and NOAA GFS, GEFS, and HRRR. Native IFS HRES surface fields retain the O1280 grid, approximately 9 km, through the Open-Meteo spatial distribution. Public ECMWF pressure profiles and ensemble fields use their available 0.25-degree distribution.
Each model run keeps its own forecast horizon and time intervals. The model explorer shows locally available raw fields, including ranges beyond the 15-day consumer forecast when the source supports them. Web maps use nearest native cells in a display projection.
Data sources: ECMWF Open Data, Open-Meteo Open Data, and NOAA Open Data Dissemination. Provider attribution and source provenance accompany the data.
Open model explorer