California’s first major Diablo wind event of the fall, increasing fire danger

Winds are expected to increase in Northern California over the next few days, eventually leading to critical fire weather conditions Thursday through Saturday.

But before wildfire danger increases, a few showers are possible Wednesday as a weak cold front grips Northern California.

The cold front disruption is predicted to weaken as it approaches the Bay Area because the parent storm is relatively far away over the Pacific Northwest, meaning rainfall totals will be light at best. A few light showers could fall along this cold front from San Francisco to Yuba City, but most areas will remain dry. Heavier showers and a slight chance of thunderstorms are possible in the northern Sierra Nevada north of Interstate 80.

Behind this cold front, temperatures are expected to drop to near freezing around the Lake Tahoe Basin on Wednesday evening. Even colder conditions are expected Thursday evening, with temperatures in the teens in Truckee and the low 20s along the Tahoe coast.

The Bay Area will see coastal drizzle Wednesday morning, followed by clearing in the afternoon as winds gradually increase and fog mixes in. Northwest gusts of up to 30 mph along the peninsula will strengthen throughout the day and continue throughout the night.

The fire danger will not be particularly high on Wednesday due to increased humidity, but winds will begin blowing from the north on Thursday, drying out vegetation and increasing fire weather conditions. Winds are expected to blow from the north-northeast Thursday night into Friday morning.

These are known as Diablo winds and have contributed to many of the Bay Area’s largest wildfires. Because these winds blow over land rather than water, they are much drier and pose a greater fire risk than the typical sea breeze.

The first major Diablo wind event of the fall will take place Thursday through Saturday. Gusts of up to 65 mph are possible along mountain ridges in the North Bay and East Bay. There is more uncertainty about how strong the winds will be in the valleys, but periodic gusts of 25 to 45 mph are likely in Wine Country, the East Bay valleys and the Peninsula, including San Francisco.

A wind advisory will go into effect at 11 p.m. Thursday for Solano County and the Delta region, including Sacramento, with gusts of up to 55 mph expected. A red flag warning for enhanced fire weather conditions is in effect for much of the Bay Area from 11 p.m. Thursday through 5 p.m. Saturday. Pacific Gas & Electric Co. has warned it could shut off power starting Thursday to prevent wildfires in parts of 30 counties.

San Francisco: Patchy morning fog will be followed by a slight chance of light rain showers midday as a weak cold front sweeps across the city. Dry weather is likely to prevail and any showers would be short-lived and light. Northwest winds with gusts of up to 30 miles per hour are expected near the water in the afternoon and evening. Highs will be in the lower 60s in the outer Sunset and Richmond counties, in the mid 60s near the Panhandle, Nob Hill and Embarcadero, and in the upper 60s in the Mission District and SoMa. Lows will be in the mid 50s.

North Bay: There is a slight chance of a midday rain shower in the northernmost portion of Sonoma and Napa counties. Otherwise, gradual clearance is expected, with highs in the 60s along the coast, low 70s in Tiburon, San Rafael and Vallejo, and mid 70s to near 80 in Petaluma, Santa Rosa, Napa, Fairfield and Vacaville. A few passing high clouds are possible overnight, but light winds should prevent fog from developing. Lows will be in the mid 40s to low 50s.

East Bay: The sky will be mostly cloudy until mid-morning and will gradually clear, leaving the afternoon mostly sunny. Highs will be in the mid to upper 60s in Richmond, Berkeley and Oakland and around 70 in Hayward and Fremont. Inland valleys will clear a little faster and should warm slightly, reaching the mid-70s. Gusts of 20 mph are expected near the Delta this evening. Overnight lows will be in the 50s, falling into the upper 40s near Danville and San Ramon.

Pacific Coast and Peninsula: Morning cloud cover is expected to gradually dissipate towards the coast by midday, but drier air moving in in the afternoon should result in coastal clearing. Comet Tsuchinshan-Atlas should be visible on the western horizon shortly after sunset if the forecast is correct. Highs will be in the upper 50s to lower 60s along the coast, mid 60s in South San Francisco and San Bruno, and upper 60s to lower 70s in San Mateo and Redwood City. Gusts of up to 30 miles per hour are expected in the afternoon. Overnight lows will be in the lower 50s.

South Bay and Santa Cruz: Skies are expected to be partly to mostly cloudy in the morning and gradually clear to reveal blue skies in the afternoon. Highs will be in the mid-70s in Sunnyvale, Mountain View, Santa Clara, San Jose, Milpitas and Cupertino and similar in the Santa Cruz Mountains. It will be cooler along the Monterey Bay coast, around 70 degrees. Overnight lows will be in the low 50s in the Santa Clara Valley, around 50 degrees in Santa Cruz, and the mid to upper 40s in Boulder Creek and Ben Lomond.

Reach Anthony Edwards: [email protected]