About

The Snowpack Explorer maps daily Snow Water Equivalent (SWE) percentiles across the contiguous United States, comparing current snowpack to the same calendar day across all available historical years. Values near 0 indicate historically low snowpack; values near 100 indicate historically high snowpack.

Views

• Gridded — ~1 km raster of SWE percentiles derived directly from NOAA SNODAS.
• Zonal — area-weighted mean SWE percentiles aggregated to USGS Watershed Boundary Dataset (WBD) units at HUC levels 2, 4, 6, and 8. Hover over a watershed for its name and percentile.

Percentile methods

• ZIG — Zero-inflated gamma distribution fit by L-moments; smooths sparse records and extrapolates beyond observed extremes.
• ECDF — Piecewise-linear empirical CDF; makes no distributional assumptions beyond the observed data.

Click the ⓘ button in the legend for reference dates and full provenance details for the current date and method.

Color scale

Colors follow the U.S. Drought Monitor convention — reds indicate low snowpack (drought conditions), white near-normal, and blues exceptionally high snowpack.

Navigation

• Date — Use the date picker or ▲▼ arrows to step through days.
• Scroll or pinch to zoom the map; drag to pan.
• Share — Copy a link to the current view to your clipboard.
• Export — Download a PNG of the current map.
• Theme — Toggle dark and light mode.

Data & processing

SNODAS daily SWE grids are available from September 30, 2003 to present. Percentiles and watershed aggregations are processed and hosted by the Montana Climate Office.