There's a small chance of snow in San Francisco Tuesday 'if timing is right'

Feb. 5, 1976: Kids mess around with snowballs near Lands End in San Francisco. Mt. Tamalpais is covered with snow in the background, during the rare snow day in the Bay Area. Feb. 5, 1976: Kids mess around with snowballs near Lands End in San Francisco. Mt. Tamalpais is covered with snow in the background, during the rare snow day in the Bay Area. Photo: Clem Albers, The Chronicle Photo: Clem Albers, The Chronicle Image 1 of / 27 Caption Close There's a small chance of snow in San Francisco Tuesday 'if timing is right' 1 / 27 Back to Gallery

Will history repeat itself?

More than an inch of snow fell in San Francisco this same week 43 years ago on Feb. 5, 1976, and this week there's an ever-so-slight chance of snow in the city "if the timing is right," says forecaster Jan Null, who runs private forecasting service Golden Gate Weather Services.

(See historic photos of times when it snowed in San Francisco in the gallery above.)

Temperatures will be falling swiftly into the 30s in valleys and 20s at higher elevations overnight Monday and into Tuesday morning around the Bay Area, as a low-pressure system dives down from the Northwest delivering a blast of cold air.

At the same time, bands of moisture will be moving quickly across the area, and Null explains where and how much snow falls is dependent on how the waves of precipitation and cold air line up. The coldest air will be arriving Tuesday morning at the backend of the system when a lot of the moisture will already be squeezed out.

"It's such a narrow call between snow and no snow," says Null.

ALSO: Blizzard warning for Sierra through Monday night: 'Even a short walk could be deadly'

Snow accumulation is in the forecast for elevations of 1,500 feet to 2,000 feet, and Null says there's a high probability Bay Area residents will wake to Mounts Diablo, St. Helena and Hamilton iced in fresh powder. "That's where showers linger," says Null.

Locations at 1,000 feet - such as the East Bay hills and Skyline Boulevard at the Summit of the Santa Cruz Mountains - could also receive a dusting. Again, "It's a matter of whether the cold air coming in and the showers phase together," he says.

Just south of the Bay Area, the Santa Lucia Mountains in Big Sur are expected to see up to a foot of accumulation on the ground, and snow is also highly likely in the Redding area at 500 feet as, Null explains, "cold air gets trapped in the Northern Sacramento Valley."

In the Bay Area, snowfall at 500 feet is most likely in the North Bay, the including Sonoma and Napa valleys, but Roger Gass, a forecaster with the National Weather Service, says it's unlikely to stick to the ground and could be mixed with rain.

As for San Francisco, Null says it's "not impossible" Twin Peaks and Mount Sutro, both at about 900 feet elevation, will see snow, but "the odds are less" because temperatures warm up near the ocean.

MORE: Chilly Bay Area storm forecast to spray local peaks and some valleys with snow

The NWS warns snow accumulation could impact motorists on Highway 17 over the Summit in the Santa Cruz Mountains and on Highway 29 at Robert Louis Stevenson Park in Calistoga.

In the valleys, Bay Area residents will see a nasty mix of severe weather with heavy rain and possible thunder, lightning and small hail. Conditions will be blustery, but this system isn't expected to deliver widespread high-winds into valleys as Friday's storm did.

The skies are forecast to clear Tuesday afternoon and conditions will remain dry through at least Friday when a weaker system could bring more rain. Temperatures will remain cool through the week with daytime highs in the low 50s and overnight lows in the 40s.