Sep 17, 2021
A late-season trough during the monsoon, just off the southern US coast, promoted deep southerly flow from the surface through mid levels of the troposphere. This in combination with a moisture axis extending up from Sonora and marginal afternoon instability promoted the development of isolated thunderstorms across southeast California and southwest Arizona. With just enough speed shear, a few storms trained or redeveloped over the same areas resulting in localized flooding impacts with average
Source: NOAA National Weather Service Storm Events Database (event 986963). Narrative written by NWS staff at the time of the event.
This event is one of many recorded floods in Riverside County. See the full FEMA flood zone map, NFIP claim totals, and disaster history for the area.