‘Unusual’ monsoon weather hits Southern California, bringing chance of mountain thunderstorms

Forecasters are predicting warmer-than-normal temperatures this week, with a chance of afternoon monsoonal thunderstorms over the eastern San Gabriel Mountains through Saturday.

Southern California will enter a weak “monsoon flow” in the next few days, with moisture and muggy weather coming from the Gulf of California, said Tom Fisher, a meteorologist with the National Weather Service in Oxnard.

The weather event is expected to primarily affect higher-elevation areas in Los Angeles and Ventura counties. The best chance of storms will be in the San Gabriel Mountains, with increasing likelihood as the system heads east, according to meteorologists.

Southern California’s monsoon season is typically from mid-July to September.

“We would usually expect a ‘May gray’ and ‘June gloom’ kind of pattern first,” Fisher said. “So this is a little more unusual.”

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Summer weather is headed for Southern California this weekend. How long will it last?

Warmer than normal temperatures are headed to Southern California this weekend and early next week, according to the National Weather Service.

May 12, 2023

Rain is unlikely this week in inland areas of Southern California, although there may be partly cloudy skies through Wednesday. Moisture is expected to increase within the next few days, with an about 10% chance of isolated thunderstorms in higher elevations starting Tuesday, according to the weather service.

By Wednesday, the chance of mountain thunderstorms will increase to 20%, Fisher said. Should storms develop, they will probably be dry or produce little rainfall, with precipitation evaporating before reaching the ground.

Temperatures are expected to climb to the lower to mid-90s across valley and desert areas through the middle of next week.

Temperatures will remain cooler in coastal areas, with low clouds and fog rolling in overnight and lasting into the morning, meteorologists said.

Monsoons in Southern California occur when a shift in the weather pattern over the Four Corners states — Utah, Colorado, Arizona and New Mexico — causes winds to rotate and brings muggy air or rain to the region. During this time, more moisture is in the air and temperatures are higher.