Will there be snow in San Francisco? It’s hard to say, said Rick Canepa, meteorologist for the Bay Area National Weather Service.
About 1/10 to 1/15 inch of rainfall is forecast for San Francisco by 7 p.m. to 10 p.m. Thursday, with an additional 3/4 to 4/5 inch of rain possible overnight, Canepa said. Whether that precipitation will result in snow depends on how cold the air will be, Canepa said.
If snow were to fall, it would most likely be on San Francisco’s highest elevations like the Twin Peaks and Mount Sutro, Canepa said.
“This is really difficult to predict even in the short term because there are so many different variables at play,” Canepa said.
A woman photographs snow falling in San Francisco on February 5, 1976.
Clem Albers/The Chronicle 1976
San Francisco hasn’t seen snow since 1976, when several inches of powder fell across the city, leaving a thin layer of snow over city streets.
By Thursday night, the snow line — the height at which snow is possible — will fall to 500 feet, according to San Francisco Chronicle meteorologist Gerry Díaz. This increases the likelihood of snow on San Francisco’s highest peaks between 1 a.m. and 8 a.m., Díaz said.
“Up to dusting is possible, along with some ice pellets in the mix,” Díaz said.
Some of the factors that determine whether it will snow overnight are the weather variations with altitude and the effects of the ocean, Canepa said. Southwest winds bring milder air from the ocean — sea surface temperatures are around 49 to 51 degrees, which is above freezing, reducing the chance of snow, Canepa said.
Colder air will move to San Francisco early Friday morning, but the city will also be at the “end of precipitation,” Canepa said. The likelihood of snow or other freezing precipitation will depend on the timing of those two events, Canepa said.
By midmorning, rising temperatures will raise the snowline too high to allow for further possible dusting on San Francisco’s peaks, and precipitation will become a mix of ice pellets and rain, Díaz said.
On February 5, 1976, snow fell on San Francisco, including the Sutro Tower.
Art Fresh/The Chronicle 1976
The best chances of seeing snow are in the inner parts of the Bay Area like the North Bay Hills or the East Bay Hills, Canepa said.
There is a 38% chance of seeing an inch of snow down to the valley floor near Healdsburg or Cloverdale, Bay Area NWS meteorologist Brian Garcia said in an update Thursday afternoon.
Snow covered the Marin Headlands north of the Golden Gate Bridge on February 5, 1976.
Art Fresh/The Chronicle 1976
The “vast majority” of snow that falls — snow that stays on the ground — will be over 1,000 feet in the Bay Area, according to Garcia.
Some snow up to 500 to 1,000 feet is expected in the Bay Area overnight and through Friday, according to a tweet from UCLA climate scientist Daniel Swain. “Novel flakes” and sleet — supercooled water droplets that freeze on snow, also known as soft hail — are seen at even lower elevations, Swain wrote.
Some snow fell in the North Bay, East Bay and Santa Cruz Mountains throughout Thursday, according to photos and video shared on Twitter. Sleet crashed on a beach in Santa Cruz on Thursday afternoon.
Reach Claire Hao: claire.hao@sfchronicle.com; Twitter: @clairehao_
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