Temperature whiplash is expected in California this week. The chill that blanketed the Bay Area will be gone by Wednesday afternoon, leaving the door open for a high pressure system hundreds of miles away to move over Mexico.
Weather models predict warm air from this week’s anticyclonic system will extend into northern California by Friday. Depending on the timing of our arrival, parts of the Bay Area could hit 80 degrees for the first time this year.
return of warm, dry air
Meteorological models support this high-pressure system harnessing the warm air of Mexico’s Chihuahuan desert. The epicenter of the high is expected to extend into western Texas, New Mexico, Arizona, and southern California from Wednesday afternoon through the rest of the week.
Residents of Los Angeles and San Diego will see daytime temperatures rise by a few degrees by that time. Southern California residents expect temperatures to rise by 5 to 7 degrees as the center of the high pressure widens by Thursday.
This sharp rise in temperature looks set to reach most of the Bay Area and Northern California around Friday, with residents of the Sacramento Valley and Bay Area interior cities — Walnut Creek and San Jose — experiencing their first 80 degrees. There is a high possibility that this year will be a ○ degree day.
San Francisco could see daytime temperatures approaching 70 degrees by Friday, but residents along the bay and delta are about to hit mid-to-high 70s. Depending on the timing of Friday’s anticyclone, temperatures could exceed 80 degrees at some weather stations in inland cities.
Baron/LynxOn Friday, Santa Clara, San Ramon, Livermore and the North Bay Valley will most likely exceed 80 degrees. This is assuming the high-pressure system can blow away the sea breezes that typically occur around 1:00 PM.
European weather models still rely on the idea that Friday’s sea breezes reach the coast and wind up in the gulf and delta earlier in the day. just enough to shave off some of the volcanoes, lift some clouds, and keep temperatures in inland valleys below 80 degrees. Sea breezes and coastal clouds may be blown away in time for the to rise into the low 80s.
Wednesday breakdown
San Francisco: A stray patch of fog may hang over the west-facing hillside this morning before the sun’s rays burn it all away. Mostly sunny skies are expected for the rest of the day, but the city’s cold air pushes in as temperatures rise above 60 degrees on the west side.
Highs in the high 50s are expected for most of the city this afternoon, though a few patches of high 60s are expected, especially over Dolores Park and Noe Valley, east of the Sutro Tower. may develop. Cool winds start blowing after 2pm, with winds of 25 mph. These winds will sweep away the remaining 60 degrees by late afternoon.
Cold nights return tonight as winds ease and temperatures drop to the high 40s downtown and mid 40s at the water’s edge. A few pockets around Twin Peaks and Mount Davidson, he can even drop to 39 degrees overnight depending on how fast the wind stops by midnight.
Peninsula and Pacific Coast: Fog is likely this morning along Highway 92 between Half Moon Bay and San Mateo. This includes the portion of the foothills facing the I-280 corridor south of San Andreas Lake. Most of the fog will be gone by 9:00 a.m. and can turn to clear skies for the rest of the day.
Look for daytime temperatures in the low fifties along Highway 1 between Half Moon Bay and Pacifica. A cold wind blows on the surface of the water. These winds are likely to reach 25 mph after 2pm, keeping temperatures in the high 50s along San Bruno Gap, including Daly City, Millbrae, and San Francisco International Airport. Residents south of Millbrae along the 101 Corridor are protected from most of these winds thanks to the hillsides and mountains of San Mateo County. The impact could push temperatures into the low 60s in Redwood City, Foster City, and Atherton.
Cold nights return tonight as winds ease and temperatures plummet to mid-40s along the coast and Gulf and below 40s along the rest of the peninsula. Some pockets of hills and mountains like Borrell Hill and Sierra Morena can drop to 30 degrees or more overnight.
North Bay: Aside from the fog in the Mayacamas Mountains this morning, residents of Marin, Sonoma, Napa and Solano counties are looking forward to clear skies.
Cooler winds picked up after 1pm today with 30 mph winds blowing at Point Reyes and Bodega Bay. Some of these winds head into the San Francisco Bay, reaching Tiburon, San Rafael, and Novato, keeping daytime temperatures along the bay in the low sixties. Cooling effects will move northwards in the afternoon and extend through Santa Rosa, Napa, and the Petaluma Valley, with possible peaks in the mid-1960s.
That cool wind is unlikely to reach the Solano County delta. A combination of cold air masses and clear skies will bring nighttime temperatures in the mid-40s in the bay and delta and in the high 30s to low 40s in the inland valleys.
East Bay: Oakland and Berkeley Hills residents may see fog by 9am this morning, while stratus (or high fog) is likely in parts of the Diablo Range. Clear skies return in the morning and remain so for the rest of the day.
Despite the strong sun this afternoon, daytime temperatures are expected to hit only the low 60s in Richmond, Albany, Oakland, Alameda, and most of Interstates 80 and 880. This is because cool Gulf breezes are expected to arrive by 1pm, cooling the area just before peak heating hours. Some breezes reach the Contra Costa County side of the delta, but temperatures can reach the mid-60s in Concord, Pittsburgh, and much of the San Ramon and Livermore Valleys, including Walnut Creek and Dublin.
Clear skies, gentle breezes and frigid air masses overhead bring the chill back after sunset, dropping temperatures to 40 degrees on the water’s edge and 30 degrees on the hillsides and inland valleys.
South Bay and Santa Cruz: Cool breezes from the Pacific blow into Monterey Bay throughout the day, keeping afternoon temperatures in the high 50s in Capitola, Soquel, Watsonville, and Aptos. Some of this wind enters the Santa Cruz Mountains and the 101 Corridor between Morgan Hill and Gilroy, dropping temperatures just enough to keep daytime highs above her 60s.
The breezes of Monterey Bay don’t seem to reach the Santa Clara Valley. Instead, San Jose residents can expect cool breezes from the San Francisco Bay, with winds of 25 mph in Milpitas and North San Jose. Look for daytime highs in the high sixties north of Berryessa BART Station and the eastern foothills of the Santa Clara Valley, but residents of the rest of the valley can expect highs in the high sixties this afternoon.
Temperatures across the region look to plummet tonight as winds ease and cool air from higher levels of the atmosphere accumulates in the valleys. It is expected to be in the high low to low 40s.
Contact Gerry Diaz: gerry.diaz@sfchronicle.com; Twitter: @geravitywave
