‘Muggier Than Usual’: Thunderstorms Possible as Monsoonal Moisture Spreads through SF Bay Area

San Francisco and other parts of the greater Bay Area could be in for a summertime thunderstorm more often found in cities like Tucson or Phoenix today.

That’s because monsoonal moisture from the Gulf of California—that normally steers toward the desert southwest—is headed toward the region. The unusual conditions are bringing the chance of thunderstorms and rainfall around the bay late Sunday and into Monday.

While San Francisco is accustomed to its low-hanging fog layer, the moisture is producing clouds high up in the sky.

“It might feel a little muggier than usual,” said Jeff Lorber, a meteorologist with the National Weather Service Bay Area.

Isolated high-based rain showers will be possible today as monsoonal moisture spreads over the region. However, widespread rainfall is not expected at this time. The potential for thunderstorms will also increase tonight into early Monday morning. #CAwx #BayAreaWX pic.twitter.com/F2ec7p2hoP

— NWS Bay Area (@NWSBayArea) July 31, 2022

Lorber said the region has already seen showers because of the monsoonal moisture, but high up in the atmosphere with the water evaporating before it reaches the ground.

Lorber said thunderstorms are possible Sunday night through most of Monday, but couldn’t say whether San Francisco in particular should expect one. 

“These types of systems are hard to predict,” Lorber said. Rainfall is also possible from Sunday night through Monday night, he said.

The potential for thunderstorms also increases the fire risk for the region, especially for parts of the Bay Area that have not seen rain.

The Golden Gate Bridge is shrouded in fog while visitors enjoy the recently-opened Presidio Tunnel Tops Park in San Francisco, California, on Sunday, July 31, 2022. High humidity and overcast skies made for muggy conditions throughout the city. | Don Feria for The Standard

“Whenever there is lightning, which is possible—not likely but possible—that definitely enhances the fire risk because lightning could strike when there is no rainfall,” Lorber said.

California firefighters are already currently battling the McKinney Fire in the northernmost part of the state, Siskiyou County. The blaze, near Yreka, began around 2 p.m. Friday and has since burned more than 51,000 acres as of early Sunday, according to Cal Fire. It remains active and uncontained. 

#RedFlagWarning remains in effect for Siskiyou County from 2 pm to 11pm for abundant lightning on dry fuels. This is #CriticalFireWeather so use caution outdoors. More tips: https://t.co/upBwccxXFO pic.twitter.com/2M6oRa24bz

— CAL FIRE (@CAL_FIRE) July 31, 2022

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