{"id":"snow-water-equivalent","slug":"snow-water-equivalent","name":"Snow Water Equivalent Dataset","description":"Monthly snow water equivalent from 847 automated stations across the mountain west and Alaska, from 1963. Not how deep the snow is — how much water is in it, which is the quantity a river responds to when it melts.","methodology":"Collected from the automated SNOTEL network, where each station weighs the snowpack on a pressure pillow every day. Hydrionis reduces the daily record to monthly means, as it does reservoir storage and for the same reason: snow water equivalent is a storage quantity, and what is held in the snowpack this month is the same kind of fact as what is held in the reservoir this month. A month is published only where the station reported on at least twenty of its days. Inches are converted to millimetres and the publisher unit is recorded alongside. The same service publishes a second network of manual snow courses whose records reach back to 1910; those are a different measurement — a person taking cores near the first of the month — and are deliberately not mixed into this record.","domains":["snow-ice"],"metricIds":["snow-water-equivalent"],"subjectScope":"Automated snow monitoring stations in the western United States and Alaska","cadence":"monthly","version":"1.0.0","released":"2026-08-31","changelog":[{"version":"1.0.0","date":"2026-08-31","summary":"First release: the water in the snowpack, where Hydrionis previously held only its depth.","additions":["Monthly snow water equivalent for 847 stations, the earliest from 1963."]}],"limitations":["A value of zero is a measurement, not a gap: for most of these stations the snowpack is gone by July and the instrument reports that it is. Reading those months as absence would remove the very values that show when the melt finished.","This is a point measurement on a mountain, not a catchment average. A single pressure pillow can miss drifting and wind scour, and a station is not the snowpack of the basin around it.","Stations sit where snow reliably accumulates, which is high and often north-facing. The network describes mountain snowpack and not the lowlands the meltwater runs into.","Monthly means smooth a quantity that can change sharply in a warm week. The peak of a snowpack, and the date it melted out, are not recoverable from a monthly mean alone.","Coverage is the western United States and Alaska. There is no equivalent record here for the Alps or Fennoscandia, where Hydrionis holds its deepest river records."],"context":{"hydrionisClass":"water-driver","whyHeld":"Snow is water in storage, waiting. In a snow-fed catchment the river’s year is decided months before the melt begins, by how much water accumulated on the mountain — which is why a spring flow forecast is really a snowpack measurement. This is not water in a river; it is water on its way to one.","waterRelevance":["Spring and summer river flow in snow-fed catchments","Reservoir inflow and refill","Drought where a winter failed to deliver snow rather than rain","Melt timing, and its shift over a long record"],"suitableUses":["Snowpack at a station against its own history","Setting a winter’s snowpack beside the following summer’s river flow, with the distance between them stated","Comparing a season with the same season in other years at the same station"],"unsuitableUses":["Catchment snow storage — that needs a spatial product, not an average of the stations that happen to exist","Inferring a volume of water in a basin from station depths","Comparing stations with each other as a statement about which mountain holds more snow, when elevation and aspect differ"],"joinDimensions":[{"kind":"time-only","on":"Shared monthly periods with any other Hydrionis series","limitation":"A shared time axis supports showing two series together and nothing more. A snowy winter above a high-flow spring is a coincidence until a catchment connects them."}],"relationshipConfidence":"contextual","eligibility":{"api":true,"download":true,"overlay":true,"publicPage":false}},"observationCount":375923,"seriesCount":847,"subjectCount":847,"from":1963,"to":2026,"sourceIds":["us-nrcs-snotel"],"units":["mm"],"redistributable":true,"commerciallyReusable":true,"citation":"Hydrionis (2026), Snow Water Equivalent Dataset, version 1.0.0. Retrieved from https://hydrionis.com/data/datasets/snow-water-equivalent/","downloads":[{"file":"/downloads/observations-snow-ice-us-nrcs-snotel.csv","format":"CSV","label":"snow-ice observations from NRCS (375,923 rows)"}],"apiPath":"/api/v1/datasets/snow-water-equivalent.json","lastFetched":"2026-08-31","fields":[{"id":"snow-water-equivalent","name":"Snow water equivalent","definition":"The depth of water that would result if a snowpack melted completely — the water actually stored as snow.","unit":"mm","nativeGeography":["monitoring-station","grid-cell"],"comparabilityNotes":"This is the operationally meaningful snow metric for water supply, because it states the volume of water held in storage rather than the thickness of the snow."}]}