Holiday Week Forecast: Wet Weather, and Then More Wet Weather

Updated 1:55 p.m. Saturday, Dec. 21

Here is weather forecasters' holiday travel advice in brief for those planning trips in and around the Bay Area and Northern California: Be prepared to deal with off-and-on wet weather from now through Boxing Day and a bit beyond. (Boxing Day, forecasters may or may not tell you, is the day after Christmas.)

But while weather models and their human interpreters agree we'll be seeing episodes of rain in the lowlands and snow in the mountains over the next week, the storms to come promise only light to moderate amounts of precipitation. So neither blizzard nor toad-strangler (a heavy downpour) is foreseen in the coming days in these parts.

And temperatures: They'll be on the cool side throughout, with highs mostly in the 50s and lows in the high 30s to mid-40s in most of the Bay Area (highs in the low 30s in the mountain resort areas with lows in the upper teens and 20s).

Caveat: Keep checking the forecasts. The go-to sources: National Weather Service San Francisco Bay Area and National Weather Service Sacramento.

Here's a day-by-day breakdown:

Saturday and Sunday, Dec. 21-22
Bay Area: A cool, cloudy day with rain developing over the North Bay counties late in the evening as a cold front approaches from the west. The heaviest rain in the San Francisco-Oakland area and South Bay into the Santa Cruz Mountains is expected early Sunday morning with showers anticipated throughout the day. Rainfall amounts will range from a quarter inch or less in the typically drier South Bay locations (San Jose, for instance) to as much as an inch in the central Bay Area (Richmond, Oakland, San Francisco) to an inch-plus in Marin County and up to 2 inches in the predictably soggy reaches of the Russian River drainage in northwestern Sonoma County. The weather system is also expected to bring gusty winds, prompting the National Weather Service to post a wind advisory for the East Bay Hills and the Diablo Range (in southeastern Alameda County and eastern Santa Clara County). Sustained winds of 25 to 35 mph with gusts up to 50 mph are forecast.

Mountains: The National Weather Service has posted a winter weather advisory for areas above 4,000 feet from 10 p.m. Saturday through 10 p.m. Sunday. Snowfall forecasts are rather light — just 4 to 7 inches except over the very highest terrain, where 1 to 2 feet could fall. If you're headed into the mountains, be ready for snow- and ice-covered roads and brief periods of whiteout conditions. The usual cautions apply: Carry chains unless you have a four-wheel drive vehicle with snow tires on all four wheels, and make sure you have food, water and warm clothes in case of extended highway delays.

Monday-Tuesday, Dec. 23-Christmas Eve:
Bay Area: No rain is forecast Monday. The latest thinking on Tuesday, Christmas Eve, is that it will be mostly cloudy but dry, with rain in the overnight hours of Christmas morning. But the National Weather Service notes Saturday afternoon that weather models have been inconsistent and forecasters' confidence on timing and rainfall amounts is low.

Mountains: A 20% to 30% chance of snow is forecast both Monday and Tuesday, with only light accumulations expected.

Wednesday-Friday, Christmas Day-Dec. 27:
Bay Area: Rain, especially in the afternoon. Showery weather possible Thursday. The latest forecast (Saturday, Dec. 21) foresees dry and sunny weather Friday.

Mountains: Those 20%-30% snow chances? They persist into throughout the week, again with only light accumulations expected.