Storm Report for August 30-31, 2021

Last updated at 11 AM on September 7, 2021

Impacts: Heavy rain with significant flash flooding, wind damage, and unfortunate loss of life.

Fig. 1. Mosaic radar imagery from 10 AM on Aug. 30, 2021 to 1 AM on Sep. 1, 2021.

During the afternoon of August 30, 2021, an outflow boundary moved from the Colorado River into the Coachella Valley with thunderstorms forming along and behind it. Several reports along Interstate 10 between Blythe and Desert Center indicated 40-50 mph winds and locally dense blowing dust. Visibilities were frequently below one mile with a few localized lower observations near typical dusty regions. Measured observations along this boundary as it entered Coachella Valley continued to support wind gusts potentially as high as 50 mph with Thermal/Palm Springs Airport recording a 49 mph gust. Many other nearby observational platforms reported wind gusts near 30 mph. The strong winds resulted in 33 downed power lines, cutting off power to the North Shore area.

Rain gradually dissipated late on Aug. 30, 2021. The environment became even more favorable for strong thunderstorms and heavy rain on the afternoon of Aug. 31, 2021. Heavy rainfall associated with nearly stationary thunderstorms occurred over much of southeast California and southwest Arizona. Widespread rainfall of 0.5 to 1.5 inches occurred, as estimated by gauge adjusted radar data, with scattered pockets of 2 to 5 inches. The most intense rain occurred in northeast Imperial County along California State Route 78, where nearly 7 inches of rain is estimated to have fallen within five hours. This resulted in significant flooding within Milpitas Wash, damaging the highway and causing it to be closed for an extended period. One vehicle was caught in the floodwaters and swept off the highway. A multi-agency search-and-rescue effort to locate two occupants was conducted. The strong thunderstorms also caused over 100 power poles to be knocked down across northeastern Imperial County.