Forecast Slopes is the ski room of the Forecast Network. Forecast Flakes covers winter weather for the country — what falls, what has to be plowed. This covers the mountain: a ski area as three thousand feet of vertical rather than a dot on a map.
415 named lift-served ski areas in the Lower 48 and 74 nordic centres, assembled from OpenStreetMap. Base and summit are the lowest and highest lift terminal, read off AWS terrain tiles under all 4,183 lower-48 lifts. Each area is cut into 500-foot bands — 1314 of them — carrying acreage, mean slope, mean aspect and the PRISM 1991–2020 precipitation normal at that height. A further 46 areas are real lift-served terrain OpenStreetMap has not named; they are counted here and withheld from the table, because naming one after the nearest town would be inventing a fact.
Each resort page leads with a server-rendered 3D portrait of its own mountain — USGS 3DEP terrain under USGS orthoimagery, photographed from the slope's own mean aspect — with the forecast painted on by elevation band and the snow line drawn on the terrain itself, updated each cycle. Ships as an image, so the page needs no JavaScript; a separate /3d/ flyover offers the interactive view, kept off the search index. Rolling out across the mountains now.
Band-by-band temperature and precipitation from HRRR, RRFS and the NBM, with the lapse rate diagnosed each cycle and precipitation carried onto the terrain by a PRISM ratio. The number that matters most is the rain/snow line drawn through the column. HRRR's full winter suite — asnow, snod, the categorical p-type flags — is already in the network's archive and unread by any site on it.
Every cycle stored and scored against SNOTEL, which reports hourly at a surveyed elevation. 123 of these ski areas have a SNOTEL within 10 km, 145 within 15. No ski forecast product publishes an ongoing, public score — the strongest of them describe accuracy as a claim, or as something coming later. The ledger is the one thing here that cannot be copied quickly, because it takes a season to accumulate.
Snowmobile trails, nordic centres and backcountry zones are the next datasets. Trail networks are a state-by-state patchwork — Michigan and Minnesota publish statewide GIS, Wisconsin's is county by county — so OpenStreetMap's route=snowmobile relations are the single consistent national source, with state DNR data layered where it exists.
Geometry OpenStreetMap via Overpass · elevation AWS Terrain Tiles · climatology PRISM, Oregon State · observations NRCS SNOTEL and NOHRSC · models NBM, HRRR and RRFS via the network's own archive. Method and measurements are written up in research/downscaling.md.