Here’s where Saturday’s ‘polar low’ will kick up the strongest winds

A polar low will result in consistent winds from the northwest on Saturday afternoon, with gusts up to 35 mph possible along the coast, bayside and delta.

STORM FORECAST: Another rare weather system is headed for California. Here's a timeline of storm impacts

A low-pressure system off the coast of Alaska, commonly referred to as a polar low, is forecast to bring bitter cold air to the Bay Area this weekend. This cold snap will be driven by the system's northwest flow and will peak Saturday night. But that flow will also raise gusty winds Saturday afternoon, especially along the coast, San Francisco Bay and the delta.

Depending on how early the polar low arrives, residents by the water could deal with gusts as high as 40 mph by Saturday afternoon, a precursor to the more turbulent weather coming early next week. Here's a look at where some of the windiest locations are forecast to be today, and why those areas might end up being among the first places to get rained on once more unsettled weather returns.

Winds from the northwest are forecast to gust above 30 mph along the coast and most of the west side of San Francisco. Gusty winds are also on tap this afternoon for the wider Bay Area.

The polar low will gradually reel in cold air this weekend, dropping nighttime lows to freezing in some inland valleys. That cold air will be carried by the low's northwest winds, which are forecast to pick up Saturday afternoon.

Because of the large volume of cold air, there will be a constant flow of northwest winds between 6 a.m. and 9 p.m., resembling an atmospheric conveyor belt between Alaska and California. Winds will pick up along San Francisco's west side and most of the coastline in Sonoma, Marin, San Mateo and Santa Cruz counties. These winds are forecast to reach 40 mph by the water, with gusts up to 50 mph possible near Point Reyes, Bodega Bay, Half Moon Bay and along most of Highway 1 between Sonoma County and Monterey Bay.

Some of these gusts will make it east of the Golden Gate Bridge and into San Francisco Bay, where they’ll spread out to most of the communities along the neighboring bays and delta. Oakland, Richmond, Tiburon and Concord could see afternoon gusts reach 30 mph, with temperatures quickly falling from highs in the upper 50s to the upper 40s by the evening. Winds are then slated to gradually subside tonight.

Temperatures will quickly rebound by Sunday morning and climb to the upper 50s and lower 60s before the next wave of constant northwest winds Sunday afternoon.

This battle between the cold, winterlike air and the warm March sun will only amplify the unsettled weather that's coming early next week.

San Francisco: Consistent chilly winds will arrive across most of the city Saturday, with west side neighborhoods like the outer Sunset and Richmond districts bearing the strongest gusts this afternoon.

Residents on the west side will contend with wind gusts up to 40 mph, while exposed hillsides like Twin Peaks, Bernal Heights and Diamond Heights will generally gust closer to 35 mph. Most residents east of Sutro Tower will experience lighter winds, up to 20 mph at times. The exception will be those in high-rises in downtown, the Tenderloin and SoMa, where gusts will climb to 40 mph on rooftops above six stories.

The northwest flow will keep daytime highs from going above the mid-50s on the west side, while the natural barrier from west and north-facing hillsides will allow temperatures to reach the upper 50s east of Sutro Tower. Some of the warmest spots will be around Dolores Park, where temperatures will get two degrees shy of 60 before winds reach the Mission. Nighttime temperatures are forecast to quickly drop to the upper 30s and lower 40s by tonight.

Pacific Coast and Peninsula: Breezy northwest winds will roll up to Highway 1 between Pacifica and Half Moon Bay this morning, spreading east to the San Bruno Gap by the afternoon. Winds will quickly climb to 20 mph and begin gusting between 35 and 40 mph between 2 p.m. and 6 p.m. Look for gusts over 40 mph near Half Moon Bay and parts of the San Bruno Gap, including Daly City, Millbrae and the vicinity of San Francisco International Airport. These gusts will generally be 10 to 15 mph lighter as you head south of San Mateo and into Redwood City, Foster City and Atherton.

The chilly, northwest winds will keep Saturday's daytime highs from rising above the mid-50s along the coast and San Bruno Gap, while residents south of San Mateo along the 101 and I-280 corridors can expect slightly warmer temperatures — up to the 60-degree mark.

As winds ramp down tonight, so will temperatures. Look for lower 40s across most of the Peninsula with a few upper 30s along the foothills of the I-280 corridor, including San Andreas Lake, Woodside, Emerald Hills and West Menlo Park.

North Bay: Winds will pick up this morning on the Sonoma and Marin County coastline, reaching 50 mph by afternoon. Most of Saturday's strongest winds will be concentrated on the coast and along San Pablo Bay and the delta, including the Marin Headlands and most of Solano County. Look for gusts up to 30 mph across most of the bayside and delta, while inland valleys in Napa, Petaluma and Santa Rosa will generally experience intermittent winds in the morning and evening, gusting to 25 mph. The highlands of Sonoma and Napa's interior valleys will gust higher, up to 35 mph, in the afternoon before dying down this evening.

Expect daytime highs in the upper 50s along the coast, bays and delta, while wind-sheltered valleys inland will see highs in the lower 60s.

Those valleys will then experience temperature whiplash, as nighttime lows drop to the 30s. Frost will be likely in most of the highlands of Sonoma and Napa counties, with lows hitting the 20s in remote corners near Healdsburg, Guerneville and Calistoga. That poses a frostbite risk, especially for unhoused residents and those with limited heating.

East Bay: Contra Costa and Alameda counties can expect a breezy Saturday as winds gust between 25 and 30 mph along the I-80 and I-880 corridors, including Richmond, Albany, Oakland and Berkeley. A few gusts up to 40 mph will be possible along the East Bay foothills in Castro Valley and near Hayward, trapping some of the windiest air from spreading east of the Caldecott Tunnel and into the San Ramon and Livermore Valleys. Breezy 15 to 20 mph winds are forecast for cities like Dublin, Pleasanton and Walnut Creek, though gusts will be minimal. Look for daytime highs in the upper 50s by the water and delta, while lower 60s will be possible in the inland valleys.

Cold air will return tonight and drop temperatures to the lower 40s, though upper 30s are on tap along the foothills of the San Ramon and Livermore valleys, including Alamo, Clayton and Ulmar.

South Bay and Santa Cruz: Northwest winds will stream into the Santa Clara Valley and 101 corridor between Morgan Hill and Gilroy today, raising gusts up to 35 mph. Winds will generally taper off by evening. Coastal residents by Capitola, Soquel, Aptos and Santa Cruz can look forward to calm conditions during the day, though some of the northwest winds in the Santa Clara Valley will make their passage along Highway 17 from Los Gatos and help cool off some of the hillsides. Look for daytime highs around 60 across most of Santa Clara and Santa Cruz counties before temperatures drop below 50 degrees this evening and reach the lower 40s on the Santa Cruz coast and in the northern Santa Clara Valley, including Milpitas, Mountain View and most neighborhoods north of San Jose International Airport. Inland areas in the Santa Cruz Mountains can expect lows near freezing.

Reach Gerry Díaz: [email protected]; Twitter: @geravitywave