‘Cold trough’ from Canada paints Sonoma County with ice and frost

Icy roads caused a series of crashes Monday morning in Sonoma County, with below-freezing temperatures dipping into the 20s and dusting areas of the region with frost, but temperatures were forecast to rise slightly today before dipping again in several days.

The region should see “some patchy frost” this morning, but more water vapor in the atmosphere overnight should slow down the amount of cooling, said Rick Canepa, meteorologist with the National Weather Service.

“It shouldn’t be quite as chilly as it has been,” Canepa said.

On Monday morning, Mark West Springs Road between Calistoga and Riebli roads was shut down about 7:45 a.m. Monday after a series of individual crashes, including an overturned vehicle that landed on its roof, causing minor injuries to one person, emergency officials said. CHP officers reopened Mark West Springs Road near Fox Hunt Lane to one lane traffic by about 8:15 a.m.

Black ice also caused the Sonoma County roads department to shut down Green Valley Road near Graton. Santa Rosa hit 29 degrees about 7 a.m. and was the coldest Dec. 19 since 2012 when the mercury hit 26 degrees, according to National Weather Service records. The temperature dipped to 24 degrees in 2006.

A frost advisory was in place for Monday morning, but that would not continue today because of higher forecast temperatures. For the rest of the week, low temperatures were expected to hover in the 30s and 40s.

The frigid temperatures were caused by a large trough of cold air that was across much of the United States, said National Weather Service meteorologist Anna Schneider.

“It’s been cold across the country,” she said.

Canepa forecast dry weather in Sonoma County until at least Thursday night, when a slight chance of rain would emerge in advance of potential showers Friday afternoon and evening. Cold winds from the northwest could then bring low temperatures from Sunday through Tuesday into the upper 20s, he said.

Staff Writer J.D. Morris contributed to this story. Reach Staff Writer Julie Johnson at 707-521-5220 or julie.johnson@pressdemocrat.com. On Twitter @jjpressdem.