Parts of coastal Southern California awoke to thunderstorms Friday morning, as monsoonal moisture primed the atmosphere for lightning and downpours. But the thunderstorm that dropped up to a half-inch of rain in San Clemente and Dana Point (Orange County) wasn’t the most unusual weather phenomenon in California on Friday.
A small area of counterclockwise-spinning clouds known as a mesoscale convective vortex crossed the California-Nevada border and brought locally heavy rain to deserts of San Bernardino and Inyo counties. The National Weather Service issued a special forecast alerting of likely flash flooding near Death Valley, an area that averages less than two inches of rain annually. Rainfall rates up to one inch per hour were possible in the deserts of California and around Las Vegas until Friday evening.
#WPC_MD 0745 affecting portions of eastern California and southern/eastern Nevada, #utwx#azwx#nvwx#cawx, https://t.co/kzmWKtOXDqpic.twitter.com/JHC0RaKiBU
— NWS Weather Prediction Center (@NWSWPC) July 18, 2025
Mesoscale convective vortexes are only tens of miles wide, small compared to traditional winter storms that can extend more than a thousand miles in diameter over the ocean before slamming into California. Despite their size, mesoscale convective vortexes can be mighty, locally dropping atmospheric pressure and creating a spinning region of clouds that can travel hundreds of miles and persist for days…