Bay Area’s unusually chilly weather to linger

If you’ve been thinking that Bay Area temperatures have felt extra chilly lately, you’d be right.

Downtown San Francisco is experiencing one of its coldest Novembers ever. And while it hasn’t been extreme, temperatures have regularly been lower than average over the past few weeks.

The cold weather hasn’t been limited to just one pocket of the Bay Area. The whole region has been chillier than usual, compared with 30-year climate normals. These normals are average temperature values calculated from 1991 through 2020.

Daily low temperatures — reflecting how cold it gets overnight — have been about 3 to 6 degrees below normal this month across the region.

“It’s not a historic cold snap that we’re under, but at the same time, it is consistent,” said David King, a meteorologist with the National Weather Service’s Bay Area office.

The cold weather stems from abnormal conditions that began more than two months ago, when the remnants of a typhoon were picked up by strong winds in the upper atmosphere and whisked to California. The storm brought uncommon September rain to the Bay Area, including a third of an inch in downtown San Francisco. The city normally gets a 10th of an inch of precipitation in September.

Since then, a series of low-pressure systems have followed a similar trajectory to that initial storm.

In addition to cold-air pooling, ever-shorter days provide less time for the sun to radiate heat on Bay Area locales.

The average low temperature this year is just shy of 48 degrees, calculated from Nov. 1 to 17. This value ranks sixth coldest among average November low temperatures for the city, stretching back to 1875.

The recent spate of chilly weather may seem to be at odds with an expectation for rising temperatures because of climate change. But the climate refers to long-term averages, not just how warm or cool it gets over a few days.

In the coming weeks, temperatures will continue to stay chilly, though there will be brief warmups. As low-pressure systems move through, the weather will swing back and forth between cooler, rainy conditions and warmer, drier days.