Wet weather in the Bay Area and snow in the Sierra will last through Tuesday morning. After that, the thermometer will dip: cold air will keep temperatures cooler than normal this week, with highs in the 50s across most of the Bay Area. Nighttime temperatures will turn even colder, with lows dropping to the 30s and below 40s for most spots. The North Bay valleys and East Bay inland could approach freezing. The weather will be dry with clear skies for the next two days as the low pressure that brought the rain recedes and the high pressure sets in. By the end of the week, the wet weather will return.
The high will settle along the California/Oregon/Nevada state lines beginning Tuesday. This will give Northern California clear skies, dry conditions and light winds.
The Bay Area has been colder than normal due to recent storms – and after the clouds part on Tuesday afternoon and evening, temperatures will drop even further overnight. This is because the clouds act as a blanket, keeping temperatures stable. Clear skies will help release any relatively warm surface air into the atmosphere, making room for cooler dense air to sink. Winds will also be lighter over the next few days. These cold mornings will last all week, with the coldest morning on Wednesday.
Freezing mornings are expected in Northern California this week. That’s what the Bay Area can expect Wednesday morning.
Tuesday Breakdown
San Francisco
San Francisco will start out cold with lows in the mid 40s and morning showers. The rain will end by late morning, followed by mostly cloudy skies. In the late afternoon, the sun will slowly break through behind the clouds. Highs will reach the mid 50s. Winds will be lighter, starting from the east and moving north in the afternoon, up to 10 mph. Areas west of Highway 1 will be cool, with highs only reaching the lower 50 degrees from Outer Richmond to the Sunset District. In the Lake Merced and San Francisco State University area, highs will reach the mid 50s. Along the Embarcadero to the Presidio, highs will reach the lower 50s.
Coast and Peninsula
The morning will start low, with temperatures in the low to mid 40s. Scattered showers will end by mid-morning. Skies will become mostly sunny with winds blowing from the northeast between 5 and 15 mph. Coastal spots along the peninsula, from Moss Beach to Half Moon Bay to San Gregorio State Beach, will bottom out in the mid-50s. At Tomales Bay, Dillon Beach and Marshall will bottom out in the mid-50s. The Bolinas Lagoon area will be noticeably cooler, with highs in the upper 40s. Other North Bay coastal towns, such as Salmon Creek and the rest of the stretch of Highway 1 in Sonoma County, will hit the lower 50s.
West of Interstate 280, Daly City and Pacfica will hit the mid-50s by afternoon. Across the mid-peninsula, South San Francisco, San Bruno, and Millbrae will hit the mid-50s. Further south, Burlingame, Foster City, and Redwood City will hit the mid-upper 50s.
North Bay
Scattered showers will start Tuesday morning, but most rain will end around 9-10am. It will be a cold start for towns along Highway 101 in Sonoma County and across Napa Valley. The lows will be between the upper 30s and upper 40s. In Marin and Solano counties, morning lows will begin in the low to mid 40s. Skies will become partly cloudy by midday then mostly sunny by early afternoon. Winds will be light.
In Marin County, peaks will peak in the mid-50s from Novato to Mill Valley. Temperatures in Sonoma County, Healdsburg, Santa Rosa, and Petaluma will reach the mid-50s. In Napa County, highs will reach the mid-50s, except for the cities of Napa and American Canyon , where the highs will hit lows in the mid-50s. In Solano County, Vallejo, Suisun City, and Fairfield will hit the mid-50s.
Nighttime low temperatures will become much colder, with valley points falling in the low to mid-30s, and the rest of the North Bay around 40 degrees. Fog and frost will form overnight through Wednesday morning.
East Bay
Inner East Bay towns will experience a cold start, with morning lows in the lower 40s. Towns closer to the bay will start in the mid 40’s. The rain will continue through the morning to stop around 10 or 11am. The sky will remain mostly cloudy most of the day, becoming mostly clear in the late afternoon. Winds will be light from the northeast. Along the Nimitz Freeway from Oakland to Fremont, temperatures will hit the mid-50s by afternoon. Likewise, temperatures will reach the mid-50s for Crockett, Rodeo and San Pablo.
Along Highway 4 it will be chilly in Antioch, with highs in the lower 50s. Martinez and Concord will be a few degrees higher. Indoor spots like Livermore, Danville, Lafayette and Waldon will also hit the mid-50s.
Nighttime low temperatures will become much colder, with inland regions dropping to the mid to upper 30s, and the rest of the East Bay near 40 degrees. Fog and frost will develop overnight through Wednesday morning primarily for the Inner Valley.
South Bay and Santa Cruz
The chance of rain continues Tuesday morning, ending by lunchtime for the Santa Clara Valley. The morning will start cold in the southern bay with temperatures around 40 degrees. The sky will be mostly cloudy with occasional sunshine and light northerly winds. By afternoon, San Jose and the rest of the Santa Clara Valley will hit the mid-50s.
Along Highway 101 from Morgan Hill to Gilroy, highs will also reach the mid 50s. A chance of rain will be possible until the afternoon. About a tenth of an inch of rain is possible.
In Santa Cruz County, morning lows will begin in the upper 30s to under 40s. Rain is likely until the afternoon and foggy conditions are possible. The sky will remain cloudy at the end of the afternoon. Scotts Valley will reach the mid-50s. Along State Route 9, in Ben Lomond and Felton, the highs will be similar, in the mid-50s. Santa Cruz and the rest of the coastline, such as Capitola and Manresa State Beach, will reach the low in the mid 50s.
Nighttime low temperatures will become much colder, with temperatures falling to the mid to upper 30s. Fog and frost will form overnight through Wednesday morning.
Cumulative rainfall over the last 7 days
Impressive rain totals so far
December begins with a fair amount of rainfall. The Bay Area is above normal so far for the month. San Francisco received almost an inch and a quarter of precipitation – nearly two-thirds of an inch above normal! San Francisco Airport and Oakland Airport are about an inch above normal, and San Jose Airport is already three-quarters above normal. Santa Rosa Airport in the North Bay received more than an inch and a third of precipitation, half an inch above normal. The Bay Area expects more rain later this week.
Snowfall total of 72 hours in Northern California.
Total snowfall in the Sierra
The western slope of the Sierra has seen exceptional amounts of snow due to the series of storms. The northern, central and southern Sierra are over 100% of normal as of today.
Here are some snow totals for Sierra Ski Resort as of Monday 30 a.m.:
Boréal received 42″ in the last 48 hours
Heavenly received 25″ in the last 7 days
Kirkwood received 39″ in the last 7 days
Northstar received 38″ in the last 7 days
Palisades Tahoe received 43″ in the last 7 days
Sierra at Tahoe received 26″ at the base and 36″ at the top in the last 7 days
Soda Springs Mountain Resort received 58″ in the last 7 days
Travel to the Sierra will still be hazardous on Tuesday morning as snow is still possible. Roads can be impassable, chain checks are likely and significant delays are possible with snow-covered roads. If you have to go to the Sierra, give yourself plenty of time.
On the agenda this week
Freezing mornings, fog and freezing conditions will persist for the next two mornings. Dry afternoons with clear skies and highs in the cold 50s will remain. It looks like colder than average temperatures will continue into next week.
A series of storms
A chance of rain is forecast between Thursday evening and Friday morning. As usual, there is uncertainty in the weather pattern, as there are still a few days left. The US model GFS (Global Forecast System) predicts precipitation early Friday morning, with rain lasting until Saturday. Saturday’s storm looks larger and could potentially bring heavy snowfall to the Sierra. Then next Tuesday another system could bring more rain to the Bay Area and snow to the Sierra.
The European ECMWF (European Center for Medium Range Weather Forecasts) model has a fast system arriving on Thursday evening and ending on Friday – then another Saturday with persistent showers on Sunday.
These two models agree that the next chance of precipitation, which is forecast for the end of the work week, appears shorter and less intense in terms of precipitation than the storm forecast for Saturday, which seems particularly important for the Sierra. The Weather Wonks will continue to monitor the next chance of precipitation, as well as the timing and amount of precipitation we may receive. In the meantime, enjoy the cool, dry stretch for the next two days.
Michelle Apon is a meteorologist for the San Francisco Chronicle. Email: michelle.apon@sfchronicle.com