Rain instead of snow leaves Western mountains with smaller snowpacks

Unusually warm conditions across the Western U.S. have shifted much precipitation from snow to rain this winter, leaving many mountain snowpacks well below average, especially in parts of the Rockies and the Sierra Nevada.

This winter, the Western United States has been unusually warm and more precipitation has arrived as rain than snow. Researchers at UC Berkeley's Central Sierra Snow Laboratory report lower-than-normal snow depths near Donner Pass. Federal measurements and climate scientists say many parts of the Sierra Nevada and the Rocky Mountains are seeing snowpacks below typical levels for late January. Scientists link the pattern to warmer average temperatures that raise the freezing line and favor rain at elevations that traditionally saw snow. What is known: - The Central Sierra Snow Laboratory, at about 6,894 feet near Donner Pass, recorded precipitation near 120% of average this season but a snowpack at about 61% of average as of Jan. 23. - California's statewide snowpack measured about 66% of average for this time of year, with the northern Sierra at roughly 50% and the southern Sierra near 86% of average. - In the Colorado River watershed, federal data show the upper-basin snowpack around 61% of average and the lower-basin area about 32% of average, with some locations at or near record lows. - Climate scientists quoted in the reporting said average temperatures a few degrees warmer have pushed snowlines higher, increasing the likelihood that precipitation falls as rain rather than snow. Summary: Lower-than-average mountain snowpack reduces the season's stored water that typically contributes to spring and summer runoff, which is important for rivers and reservoirs across the West. California's reservoirs are currently above average and not classified as drought-affected, while the Colorado River basin is reporting notably low snow accumulations that align with longer-term declines in river flow. Whether late-season storms will add substantial snow is uncertain. Undetermined at this time.