Current Snowpack as % of Normal Map

Snowpack telemetry (SNOTEL) sites are automated stations operated by the USDA Natural Resources Conservation Service (NRCS) that measure snow water equivalent (SWE), the depth of water that would result by melting the snowpack at the measurement site. SWE is determined by measuring the weight of snow resting on a pressure-sensitive pillow (like a very large bathroom scale) at the SNOTEL site, and converting that measurement into inches of water equivalent.

The Current Snowpack as % of Normal map from NRCS depicts the conditions averaged across a set of SNOTEL sites that are either within or immediately adjacent to the outlined basin. For each SNOTEL site that is actively reporting data, the current SWE is calculated as percentage of the historic (1991-2020) median SWE for that date. Then for each basin, these % of normal values for active SNOTEL sites are averaged across each basin to generate the % of normal value for that basin. The number of SNOTEL sites representing each basin ranges from 1 to 31, depending on the basin and the number of actively reporting sites. This table from NRCS has the same data as in the map, but also reports the number of SNOTEL sites reporting for each basin.

Note that SNOTEL sites are point samples of complex and spatially variable basin snowpacks. Collectively, the SNOTEL sites within a basin may over- or under-estimate actual basin snow conditions, particularly if the highest and lowest elevations in a given basin (which have fewer SNOTEL sites) have unusual snowpack anomalies. Also, not all SNOTEL sites may be reporting on a given day.

For additional SNOTEL maps visit NRCS here.

For State Basin Outlook Reports, visit NRCS here and select the state from the dropdown menu.