Get ready for a taste of summer in March. A favorable offshore wind pattern will send temperatures soaring over the weekend, with downtown San Francisco having a shot at reaching 80 degrees on both Saturday and Sunday.
If an 80-degree day happens, it would be the earliest the city has reached that mark since 2004, when it hit 81 degrees on March 10. And if the city somehow reached 80 degrees on both days, it would mark an even rarer occurrence. The last time the city had two consecutive 80 degree days in March was in 2011.
The occurrence of 80-degree heat in San Francisco in March requires a very specific setup. In this case, a ridge of high pressure will strengthen and expand over Northern California and the Pacific Northwest. As the high pressure extends inland, surface winds will rotate clockwise around the center, resulting in a prolonged period of northeast winds in the Bay Area.
Northeast or offshore winds push warm and dry air across the region and are often referred to as “Diablo winds.” This weekend’s setup doesn’t quite match the typical atmospheric pattern that causes Diablo winds, but the effect is essentially the same. And it’s how we can get very warm days all the way to the coast.
A model simulation of winds just above the Earth’s surface on Saturday morning shows a strong offshore flow. (WxBell )
Regardless of whether the city hits 80 degrees, it’s going to be a very warm weekend across the region. Oakland, Berkeley and the Tri-Valley area of the East Bay should see a few 80 degree readings, especially on Sunday. Silicon Valley and the South Bay will also see temperatures rise into the 80s. And some of the typical North Bay hot spots like Santa Rosa, Napa and Fairfield should also see temperatures in the 80s on Sunday.
All across the region, temperatures will be running about 10 to 20 degrees above normal for early March. And the offshore wind should ensure that the warmth spreads all the way to the Pacific coast, where temperatures should reach the 70s in Ocean Beach and Half Moon Bay.
A ridge of high pressure (red) will edge over Northern California over the weekend, resulting in strong offshore winds that will push temperatures higher. (Tomer Burg)
Unlike last weekend, the air mass will not be humid. The offshore winds will keep things dry, and relative humidity levels will hover in the 20% to 30% range. The combination of warm temperatures, lots of sunshine and dry air will create a minor heat risk.
In any case, expect parks to be bustling and bayside beaches to be full over the weekend – and the outdoor revelry can continue later into the evening after the time change.
Weekend forecast
San Francisco: Friday will be sunny but breezy as north -winds gust up to 35 mph early in the day. Afternoon temperatures should still climb into the mid- to upper 60s, with a few sheltered neighborhoods touching the low 70s. Saturday looks warmer and calmer. Abundant sunshine will push temperatures well into the 70s across much of the city, with 80 degrees possible in neighborhoods like the Mission, Noe Valley and Potrero Hill. Sunday should stay mostly clear and warm again, with highs in the 70s and again a few 80-degree readings.
North Bay: Friday will be sunny but quite windy across the North Bay, especially in the morning. Strong north winds will gust up to 50 mph at times, especially through wind-prone areas like the Carquinez Strait, the Napa Valley and the higher terrain of Sonoma and Marin counties. Temperatures should reach the mid to upper 70s in spots such as Santa Rosa, Napa and Petaluma. Saturday will stay sunny but still breezy, particularly during the morning hours, before gradually easing later in the day. It will be warm, with temperatures in the 70s most places and touching 80 degrees in isolated spots. By Sunday the winds should relax, and the warmest temperatures of the stretch will arrive. Highs will reach the mid-70s to lower 80s across much of Sonoma and Napa counties under clear skies.
East Bay: Friday will be sunny but breezy in the morning, especially along the bayshore. Afternoon temperatures should reach the upper 60s to mid-70s. Inland valleys such as Walnut Creek, Concord and Livermore will run slightly warmer, with highs in the low 70s and gusty winds. Saturday will bring calmer conditions, more sunshine and warmer temperatures. Bayshore communities should reach the mid-70s, while inland valleys climb into the upper 70s to near 80. Sunday will likely be the warmest day of the weekend, with temperatures reaching the mid-70s to low 80s along the bayshore and across inland valleys.
Pacific Coast: Friday will be sunny and breezy along the coast from Pacifica through Half Moon Bay, with highs reaching the upper 60s to around 70 degrees. Saturday looks warmer with an offshore wind and lots of sunshine. High temperatures should climb into the low 70s along the immediate coast, with breezy north winds again producing morning gusts that will ease later in the day. Sunday will be a bit warmer, and highs should reach the mid-70s with lighter winds.
Peninsula: Friday will be sunny but windy early, especially along the bayside and exposed hills. Afternoon temperatures should reach the upper 60s to mid 70s from South San Francisco through Redwood City. Saturday looks warm and sunny, and high temperatures should reach the mid- to upper 70s across much of the Peninsula. Sunday will likely be warm again, as temperatures should reach the mid-70s to lower 80s.
South Bay: Friday will be sunny, warm and not as windy as the rest of the Bay Area. Highs should reach the low to mid-70s across much of the Santa Clara Valley. Saturday and Sunday will feel noticeably warmer. Under full sunshine, afternoon temperatures should reach the upper 70s to low 80s across most South Bay communities.
This article originally published at San Francisco could hit 80 degrees this weekend in rare March warm spell.