Debris Flow — Alpine, California

2022-08-03 · near Markleeville, Alpine, California

Event narrative

Severe flooding was reported along State Route 89 in and out of Markleeville, CA with numerous debris flows. Roadway damage was also reported, along with reports of vehicles starting to get swept away.

Wider weather episode

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.

View location on OpenStreetMap → (38.6889, -119.7357)

Source: NOAA Storm Events Database, event_id 1050965. Narrative written by the NWS forecast office that issued the report.