How a ‘low cut’ could create turbulent weather in California
An intermittent low pressure area will increase instability and the potential for turbulent weather in California this weekend.
A meandering band of fast-moving winds in the atmosphere typically transports low-pressure systems in and out of California within a day. Every now and then, systems come out of tape. With nowhere else to go, the so-called “cut-off low” will bring cloudy skies, rain and thunderstorms across the Golden State over the next few days.
Monuments of Northern California
Weather models forecast a low this weekend off the California coast. The system’s counterclockwise movement is expected to increase instability in the air, resulting in isolated thunderstorms in Humboldt, Siskiyou, Mendocino and Lake counties.
A U.S. weather model predicts up to half an inch of rain from showers and thunderstorms in northwestern California this weekend.
Baron/LynxThunderstorm activity is expected to peak from 2 to 8 PM this weekend. Isolated gusts over 35 mph will be possible. Some active wildfires in northwest California, including the Smith River Complex, received up to a half-inch of rainfall. Moist soil and expected rainfall will reduce the risk of wildfires caused by lightning strikes.
Sierra Nevada ruins
Reduced cutting is expected to increase instability in parts of the Sierra Nevada. Visitors in Yosemite, Tahoe, and Mammoth can see Thunderheads on the horizon. The highest thunderstorm chances will be from 2 to 6 PM this weekend on peaks above 3,000 feet.
Occasional lightning, along with flooding in remote passes, may pose risks. Check for updates from park rangers about road closures and seek shelter from lightning and heavy rain.
Monuments of Southern California
This system will provide much of Southern California this weekend, although residents from Santa Barbara to San Diego can expect June-like clouds in the morning followed by sunshine. A stray afternoon thunderstorm cannot be ruled out in remote corners of the San Gabriel Mountains and Ventura County.
Gulf region influences
The Bay Area is set to see a rush of offshore clouds, wind and drizzle this weekend. Rainfall on the coast will likely only reach a few tenths of an inch, while inland cities like Walnut Creek and San Jose can expect a few hundredths of an inch at best.
Thunderstorms are expected to stay out of the Bay Area, but hikers in Twin Peaks, the East Bay Hills and San Bruno Mountains can see distant thunderheads above the northern and eastern horizon in the afternoon.
This low is expected to continue through Sunday, keeping this bleak and unstable weather pattern in place across Northern California until early next week.
Contact Gerry Diaz: gerry.diaz@sfchronicle.com; Twitter: @geravitywave
