Snowstorm picks up speed, heads toward Bay Area WEATHER

I run into a lot of amazing photos in the Chronicle archives, and a large number of them were taken by Art Frisch. This March 22, 1964, photo was taken along Mt. Tamapais. The girls' names are listed as Lann Harrison and Candice Wright. Judging by the look on her face, I think the girl in the background is about to take out the girl in the foreground with a car snowball. less I run into a lot of amazing photos in the Chronicle archives, and a large number of them were taken by Art Frisch. This March 22, 1964, photo was taken along Mt. Tamapais. The girls' names are listed as Lann ... more Photo: Art Frisch, The Chronicle, 1964 Photo: Art Frisch, The Chronicle, 1964 Image 1 of / 35 Caption Close Snowstorm picks up speed, heads toward Bay Area 1 / 35 Back to Gallery

Get those parkas out now, because the snow is racing even faster to the Bay Area than forecasters had thought.

Whether that means the wet whiteness will actually stick to the ground rather than melt as soon as it hits is still up in the air - which is mighty cold as air goes, but not lock-on sure to be cold enough to create snow.

Weather expert predictions on that vary by the hour, and as with all things weatherwise, even the experts are saying the only way to be sure is when the snowflakes land on your tongue.

As of Wednesday evening, the forecasting consensus was that the target time for fluttery cold things to start dropping on the region is tonight, not Friday night, courtesy of an Alaskan cold front sweeping our way.

The first snowflakes are supposed to fall in the North Bay, but by Friday afternoon, people in downtown San Francisco could well be gawking at them as well.

The magic combination for San Francisco ground-level snow will be a swing of the thermometer into the mid-30s, and a bit of precipitation. Predictions are for temperatures in the 40s during the day, and then the 30s at night - with snow either happening or not, depending on who's talking.

"The polar express is definitely coming, so anybody commuting Friday morning who lives in the North Bay above 1,000 feet had better either stay home or make other plans," said National Weather Service forecaster Steve Anderson. "There's going to be quite a bit of snow. And there will be rain where there isn't snow."

Tonight, from Sonoma County north, about 1 inch of snow is predicted to pile up at the 1,000-foot elevation and 2 to 4 inches above 1,500 feet, he said. Beyond 2,000 feet, expect 6 inches of snow.

That means they'll be strapping chains onto tires in places like the 1,800-foot-elevation town of Angwin, north of Napa, and Highway 29 from Calistoga to Lake County, which crests above 2,000 feet in spots.

The Weather Service had issued a winter storm warning for the North Bay early Wednesday, but by evening it was downgraded to a weather advisory. As today progresses, forecasters will keep a close eye on the skies and upgrade the advisory if needed.

By Friday afternoon, snow will probably be spreading south into the core of the Bay Area, forecasters said. On Friday, or at least by Saturday morning, there is a good chance for snow at sea level in San Francisco for the first time since February 1976, the National Weather Service opines.

Or not.

"In San Francisco, everything has to line up perfectly for snow to happen, and at this point I don't think it's likely," said Jan Null, who runs Golden Gate Weather Services, a private Bay Area meteorological consulting firm. "You'll need the precipitation to come in right on top of a band of cold air, and it looks like the rain might be done by Friday evening."

Previous estimates had the snow possibly hitting sea level by Saturday morning, but the storm sweeping down overland from Alaska and Canada is moving faster than thought, meteorologists say.

By late Wednesday morning, there was snow on the northern Oregon coast at an elevation of 60 feet, Anderson said.

"It's coming fast," he said.

To purchase historical Chronicle photos of snow days, go to links.sfgate.com/ZKWO.