Friday, the first day of winter and the year's shortest day, will kick off a wet weekend as a storm moves across the Bay Area, bringing rain, cold and winds of up to 25 mph in places -- if the world doesn't end.

If we're still here, the storm will drench the Bay Area with as much as 2 or 3 inches of rain and dump lots of snow in the Sierra, with weather clearing by Christmas.

So far, the only delays in air travel are on flights in and out of Chicago, which is experiencing heavy winds. But travelers are advised to check their airlines for changes in departure times. Southerly winds were expected to bring rain to the Bay Area around midnight, shortly before the winter solstice, which occurs at exactly 3:12 a.m. Friday morning. The 5,126-year Mayan calendar ends its "great cycle" with this solstice, which has stirred a brisk discussion over whether or not the world will end on Friday.

Undaunted forecasters are predicting rain and steady winds of 10 to 25 mph, depending on location, rattling the Bay Area off and on for the rest of the weekend, according to the National Weather Service. The storm will hit the East Bay first and spread south into San Jose a couple of hours later, continuing through the early afternoon hours Friday.

The weather may actually help retailers. Carrie Williams, director of marketing at Stoneridge Mall in Pleasanton, said stores usually benefit from bad weather because the mall is dry and warm.

And this late, shoppers have few options if they hope to finish their gift list before Christmas, she noted.

The heaviest rain will start Saturday morning and extend into the afternoon.

Sunday should bring scattered showers followed by another sustained stretch of rain in the afternoon through the evening, according to the weather service.

Temperatures will be in the mid- to upper 50s, but the wind will make it feel colder.

"It's definitely going to be blustery and ugly out there," said Christine Riley, a forecaster with the National Weather Service in Monterey. "We're not seeing a clear break in the rain from late Friday morning until Saturday afternoon," Riley said.

The East Bay will get up to 3 inches of rain through Sunday evening and will experience the strongest winds, with sustained blasts of 25 mph rattling tree tops at times. The South Bay will get 13/4 to 2 inches of rain through Sunday and will be buffeted by 10-15 mph winds, with gusts of up to 25 mph, the weather service said.

The area is already above the average December rainfall, with more than a week left in the month.

One event that will remain undiminished by the expected heavy rain is the noon-5 p.m. Winter Solstice celebration in Marin County's Muir Woods National Monument.

"We do this rain or shine, wind or ice, full moon or starry night -- you name it," said Mia Monroe, a ranger at Muir Woods.

Lake Tahoe is battening down for a storm that is expected to dump a lot of snow on the Sierra.

"We're expecting 5 to 6 feet of snow with potential blue skies for Christmas," said Squaw Valley spokeswoman Amelia Richmond.

The weather service predicts periods of moderate to heavy snow Friday through Sunday night, courtesy of a low-pressure system that will remain over the Sierra through the weekend.

There could be "whiteout" conditions and lengthy travel delays, the weather service said in a bulletin. It advised travelers to consider alternate routes to avoid the Sierra passes this weekend.

Across the Bay Area, there's always a chance that a heavy gust could knock down a power line.

"If you see a downed power line, assume it is energized and extremely dangerous," PG&E spokeswoman Monica Tell warned. Don't touch or try to move it, and keep children and animals away, she said.

Report downed power lines immediately by calling 911 and PG&E at 1-800-743-5002.

The power company also warned against using candles if lights go out. The risk of fire isn't worth it, especially at this time of year when flammable decorations abound.

If you have to use a candle, keep it away from drapes, lamp shades, trees and small children.

There's a potential for the storm to affect air travel, said John Ginty, duty manager at the San Francisco International Airport, but on Thursday afternoon, the only delays were for travel in and out of Chicago. There, gusty winds have caused delays of about an hour. Ginty advised travelers to check with their airline for changes in departure times.

Bay Area News Group staff writer Heather Somerville contributed to this report. Contact Pete Carey at 408-920-5419. Follow him at Twitter.com/petecarey.

tips for bad weather
  • Don't touch any downed power lines. Assume them to be energized and dangerous. Call 911 and PG&E's hotline at 1-800-743-5002 if you see one. Keep kids and animals away from them.
  • Travelers are advised to check departure times before going to the airport. No delays are expected at the area's major airports, but that could change.
  • Heading to the snow? Check the weather. Long delays and possible "whiteouts" are expected at times. The weather service advises finding alternate routes to the Sierra passes.
  • Don't light candles if the lights go out. There's too much flammable stuff in homes during the holiday season.