Following a whiplash transition from record warmth to very heavy mountain snowfall in California, yet another swing back toward anomalous warmth (first damp, then dry)
Weather West • • general
Key Points:
- Last week’s heavy snowfall in the Sierra Nevada marked a dramatic shift from a nearly 40-day warm and dry period, causing widespread travel disruptions and leading to the deadliest avalanche in California history, which claimed nine lives near Castle Peak.
- The avalanche was triggered by a weak icy snow layer from prior warm conditions combined with an intense snowstorm depositing 4-6 feet of snow in just a few days, a risk that had been well predicted and communicated by weather authorities.
- Despite the heavy snowfall boosting snowpack in central and southern Sierra Nevada to near or above average levels, much of the rest of the Western U.S. continues to experience record low snowpack, particularly in the Pacific Northwest, Great Basin, and Colorado River Basin.
