SAN FRANCISCO (CBS SF) — The first major storm in nearly six months zeroed in on Northern California Tuesday, triggering a flash flood watch for the fire-charred areas of Sonoma County, a high surf advisory, a hurricane force wind warning for the Mendocino coast and winter storm warning for the Sierra.

The storm — described as a ‘bomb cyclone’ by forecasters — began rolling into the North Bay by late morning and was advancing on the rest of the Bay Area expected to be in full force by the evening rush hour.

A “bomb cyclone” forms when air pressure drops by 24 millibars in a 24-hour period. Forecasters said this storm’s air pressure has dropped even more quickly than that.

The National Weather Service said the flash flood watch would run from 2 p.m. to 10 p.m. Tuesday for the more than 77,000 acres charred by last month’s massive Kincade Fire.

“Moderate to briefly heavy rain rates are expected this evening as a cold front passes through the North Bay,” forecasters said. “The primary area of concern the Kincade Fire burn area as well as locations immediately downstream in northern Sonoma County. Rainfall rates of 0.50 to 0.75 inch per hour are briefly possible this evening.”

 

Bay Area Storm Leads To Flash Flood Watch For Kincade Fire Burn Zone

Sonoma County Board of Supervisors Chairman David Rabbitt says erosion control in the burn zone could be a problem. “I think the first rain after a major fire are always a worry. So the county is taking some precautions to ensure that the area is safe from any kind of erosion or debris flow,” Rabbitt said.

Teams worked at Foothill Regional Park on the eastern edge of Windsor to spread hay and build straw waddles in an attempt to hold the soil in place, said Mungo Margeia, Sonoma Regional Parks Planner.

“It prevent pollutants from being discharged directly into water bodies, Number 2, it keeps sediment from being deposited into our creeks.”

The work also helps prevent mud and ash from running into nearby neighborhoods. Streets are clear in Windsor, but the park and its three lakes could have problems if the rain continues.

“This is something that is going on, will be going on, it will continue for at least a year going forward,” Rabbitt said.

KPIX 5 Weather Center: Current Conditions, Maps, Forecast

The cold weather storm front was also expected to batter the north coast from Point Arena in Mendocino County to Point St. George in Del Norte County near Crescent City.

 

Weather Service forecasters issued a hurricane force wind warning for the region through Wednesday mornings. Wind gusts were expected to exceed 72 mph with waves expecting to be as high as 31 feet or 3 stories high. Thanksgiving week visitors to the North Coast were warned to stay away from the beaches and be on the lookout for deadly sneaker waves.

“Large breaking waves along the coast will lead to increased wave run-up on beaches with waves topping and washing over large rocks and jetties,” forecasters warned. “These large waves can be erratic and unpredictable. Use extra caution near the surf as these large waves will be capable of sweeping people into the frigid and turbulent ocean water.”

WATCH: CBSN Bay Area – 24/7 Digital News Channel from KPIX 5

The Sierra was also bracing for its first major storm of the fall/winter season. Bay Area travelers heading to the Lake Tahoe area for the Thanksgiving holiday were warned to hit the road Tuesday afternoon. A winter storm warning was set to go into effect at 4 p.m. Tuesday and last until 4 p.m. Thanksgiving day.

CHP began holding traffic on I-80 in both directions Tuesday afternoon due to multiple collisions and spinouts near Truckee and Alta. Caltrans advised travelers to expect long delays until Wednesday.

I-80 reopened in both directions around 5:20 p.m., CHP Truckee said.

Eight to 18 inches of snow was possible at lake level with winds gusting as high as 60 mph. At the higher levels near the Tahoe ski resorts as much as 3 feet of snow could fall with winds gusting to 60 mph, creating white-out blizzard conditions on the high passes on I-80 and Highway 50. Travelers should be ready for chain controls to be in place.

“Travel could be very difficult to impossible,” the weather service said. “If you are traveling for the Thanksgiving holiday … finish your travels by midday Tuesday.”

In the Bay Area, the storm was set to bring relief from the drought-like conditions of the last several months. San Francisco has gone 188 straight days without recording a tenth of an inch of rain.

The brunt of the storm was expected to roll through between 4 p.m. and 8 p.m. as the cold front pushes across the Bay Area. Steady rain, gusty winds and the possibility of a thundershower were predicted stretching from Marin to San Jose.

Forecasters predicted that the bulk of the rain, which will be heavy at times, will fall Tuesday night into Wednesday morning with 1/2 inch to an inch of rain expected at the lower levels with higher elevations seeing up to 1.50 inches and even 2 inches in the Santa Lucia mountains in Monterey County.

Temperatures are also expected to plunge. By Wednesday, snow levels were expected to lower and some early season snow could fall in the higher elevations of the Santa Lucia and Diablo range in the East Bay. Afternoon temperatures will only reach the mid-50s while overnight lows will drop into the mid-to-upper 30s with isolated low lying valleys seeing the upper 20s by Thursday and Friday mornings.

The stormy weather will also create havoc at San Francisco International and other Bay Area airports as travelers crowd terminals and flights, heading off for the Thanksgiving holiday. Airport officials warned of flight delays and advised travelers to check with their airlines.

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