Debris Flow in Alpine County, California

Grover Hot Springs state park staff reported debris flow over Hot Springs RD due to intense, heavy rainfall. Depth and damage were unknown at this time. Also, Caltrans and CHP reported boulders and rocks in the area with one part of Hot Springs RD starting to wash out. Another road was reported impassible.

A deep layer of monsoonal moisture pushed northwest and north into California, Sierra, and western Nevada in a southerly upper flow that marked the western margins of an area of strong high-pressure ridging into the Great Basin region. Thickening mid-level moisture coupled with steep afternoon lapse rates and warmer surface heating initiated deep columns of slow-moving moisture-laden showers and thunderstorms with torrential rains over the 2021 Tamarack burn scar. This resulted in widespread flash flooding and debris flows in Alpine County CA that created a number of impacts. Rainfall rates of 2.22 inches per hour were observed during the peak of the storm in Markleeville, CA which corresponds to at least a 500 year recurrence interval and possibly 1000 year, per NOAA 14 atlas.