California Flash Flood Watch, Wind and Winter Weather Advisories As Powerful Storm Heads West

A flash flood watch along with wind and winter weather advisories have been issued by the National Weather Service (NWS) in parts of California, with heavy rain, snowfall, gusty winds and potential flooding forecast for the region as a powerful winter storm heads west this weekend.

"A strong storm system will impact the western U.S. Friday through the weekend bringing heavy mountain snow, heavy rainfall, potential flooding, and strong winds. Hazardous travel is likely," the National Weather Service (NWS) warned.

A Flash Flood Watch is in place from Friday afternoon through 4 a.m. (local time) Saturday morning in the San Francisco Bay Area within the North Bay Interior Valleys and North Bay Mountains regions, including the cities of Santa Rosa, South Santa Rosa, Napa, San Rafael, Petaluma, Novato, Rohnert Park, Angwin, Lagunitas-Forest Knolls and Woodacre.

A Flash Flood Watch indicates the weather conditions could lead to flash flooding, which is most often caused by extremely heavy rainfall from thunderstorms. Flash flooding can happen very quickly and the situation could become dangerous when water levels rise rapidly.

"Steady rain will develop Friday afternoon and continue into Friday night before turning showery Saturday. Excessive rain rates and rainfall amounts Friday night from 2 to 4 inches may trigger flash flooding over the burn area. Rain rates of 0.50 to 0.75 will be possible during the cold frontal passage Friday night," the NWS warns.

Rainfall predictions in the area range from around 0.25 to 0.50 inch in the Bay Area, Ventura and Los Angeles counties (with around 0.50 to 0.75 inch locally in the foothills and mountains) to around 0.50 to 1 inch in San Luis Obispo County (with 1 to 2 inches locally in the northwest foothills).

Wind advisories are in place across several parts of California on Friday and Saturday, with winds from around 15 to 30 miles per hour and wind gusts reaching up to 50 miles per hour.

The areas under a wind advisory include the greater San Francisco Bay Area, the Central Coast and San Benito County, with some areas being protected from the strong winds, such as in some interior valleys and parts of the southern Santa Clara Valley, as well as the Del Norte Interior, Northern Humboldt Interior, Southern Humboldt Interior, Southwestern Humboldt, Fort Tejon, West Side Hills and Central Siskiyou County.

Reminder: ⚠️A Flash Flood Watch will be in effect for the Kincade Fire burn area Friday afternoon into Saturday morning as a potent cold front is forecast to move through the region. #CAwx #CAflood

— NWS Bay Area (@NWSBayArea) December 5, 2019

The most powerful winds are forecast to be along the Bay Area coast, in the hills and over the North Bay area as the cold front passes through the region on Friday.

Winter storm warnings are in effect through Sunday in parts of northern California where a strong winter storm is expected to develop from Friday, with the highest amount of snowfall expected in the Sierra Nevada Mountains and Pacific Northwest regions, with snow accumulations reaching between 1 and 3 feet, potentially up to 4 feet locally in the mountains. A Winter Storm Warning indicates roads will be covered in snow and there will be limited visibility.

"Snow combined with strong winds could significantly reduce visibility. Mountain travel will be hazardous and is not advised...while damage to trees and power lines is possible.

A Wind Advisory has been issued for the Greater Bay Area, Central Coast, and San Benito County from 10 AM Friday until 7 AM Saturday. Note that there may be areas that are sheltered from advisory winds.#CAwx

— NWS Bay Area (@NWSBayArea) December 5, 2019

"If travel is necessary, carry chains and expect lengthy delays. Snow will decrease Sunday night with dry weather on Monday," the NWS notes.

The NWS also issued a Winter Weather Advisory for the Eastern Sierra Slopes and White Mountains region of Inyo County until 4 p.m. (local time) Sunday, which means periods of snow will cause severe disruptions and difficulties for travel, with snow-covered roads and limited visibility.

Up to a foot of snow is forecast at elevation levels above 8,500 feet and between 5 and 10 inches at above 7,000 feet, with wind gusts of up to 40 miles per hour.

San Francisco Bay Area Flooding Storms 2005
A car engulfed in water as it drives through Fort Point in San Francisco during a series of wet winter storms in the Bay Area in December 2005. Getty Images