“Jan 2022 won’t be the driest on record for all of NorCal (including SF) just based on what has already fallen,” UCLA climate scientist Daniel Swain wrote on Twitter. “But it will likely be so across much of Central Valley and central/southern Sierra Nevada, particularly south of I-80 corridor.”

Swain shared a map on Twitter showing vast areas of the Golden State — including areas of Northern California and the majority of Southern California — that have seen 0.1 inches or less of rain in January. 

Far Northern California and the San Francisco Bay Area have generally seen below-normal rainfall in January but more than some of the exceptionally dry areas. The gauge in downtown SF has recorded 0.61 inches since the start of the month, compared to the 2.99 inches that are normal for this point in the month.

The dry pattern is the opposite of what California saw in December 2021 when a parade of storms soaked the state and piled up snow in the Sierra Nevada. In November, Northern California saw one significant storm, but the month was generally dry statewide. And then there was October, when a historic storm categorized as an atmospheric river drowned Northern California in rain.

Swain calls the back-and-forth between wet and dry “precipitation whiplash.”

Dry periods aren’t unusual in California in the winter and usually occur when a ride of high pressure sets up over the region. That’s the setup the region is experiencing right now.

Mike Anderson, state climatologist with the California Department of Water Resources, said the La Niña conditions that are currently present in the eastern tropical Pacific Ocean favor a wintertime atmospheric circulation with high pressure somewhere over the Pacific Ocean.

Continue reading the article from the SF Gate here.