NorCal Braces For 4-Day Rainstorm, Flash Flooding Risks

BAY AREA, CA — Northern Californians should gear up for a cold and stormy Valentine's Day as another powerful atmospheric river is set arrive and dump rain on the region for at least four days, weather officials said.

From freeze warnings to flash flooding risks — Northern California will see a full spectrum of effects from two separate systems that will move through the area this week, according to the National Weather Service.

The first storm, which is "not really" an atmospheric river, weather officials say, will bring rain Tuesday that will fall intermittently through Wednesday. It is forecast to bring around 0.5 to 1 inch of rain before the region gets a break in the rain on Wednesday.

"At this point some of you will think we over-hyped this system. I just ask that you save that critique for another day as the real show arrives early Thursday morning," NWS forecasters said Monday.

"The second push of moisture is definitely an atmospheric river."

During the second storm, an inch and a half to 3 inches of rain are expected across the Bay Area. However, the coastal mountains are expected to see the most rain, at least 5 inches, according to multiple reports.

The significant storm and the cold air it brings could also bring light snow to the higher peaks around the Bay Area and major snowfall to the mountains.

Earlier this month, other atmospheric rivers caused disastrous situations for NorCal residents. Gusts topping 60 mph in some areas inundated streets, brought down trees and electrical lines throughout the San Francisco Bay Area. Rain also triggered landslides and other hazards that prompted evacuations across the region.

Then, a home slid into the Russian River while a woman had to be rescued from her flooded car. Two storm-related deaths were also reported.

It's unclear just whether this week's storm will do as much damage.

Unlike the last few storms, the heaviest rain this week will be concentrated across the Santa Cruz Mountains, South Bay and East Bay interior, the San Francisco Chronicle reported.

Heavy rain poses a "marginal" 5 to 15 percent and "slight" 15 to 40 percent chance of flash flooding throughout the region Wednesday and Thursday in parts of the Bay Area where drainage is poor, forecasters said.

“With this storm, it’s not going to take much water to make the streets a little more dangerous,” Karleisa Rogacheski, a forecaster with the National Weather Service in the Bay Area, told SFGATE.

Before that powerful second storm hits, temperatures could fall dramatically in some areas. In cities like Sonoma and Livermore, temperatures will drop into the low 30s as early as Monday night. In San Francisco and Berkeley, temperatures will drop into the low 40s beginning Monday.

Frost Advisories and Freeze Warnings were also issued for inland portions of the Bay Area for Tuesday morning.

While Southern California has recorded its dryest start to a rainy season on record, Northern California has enjoyed a much wetter winter thus far amid La Niña conditions.

Between July 1 and Feb. 7, downtown San Francisco has received just over 15 inches of rain. The region must get just under 23 inches of rain by the end of the season to be in the "normal" range, according to data from the NWS.

This juxtaposition is likely happening because La Niña tends to tilt the odds toward dryer than normal in SoCal and wetter than average weather in NorCal.

The National Oceanic and Atmospheric Administration declared a La Niña pattern in January, which is expected to persist through April. La Niña happens when cooler than normal sea surface temperatures are reported in the equatorial Pacific

READ MORE:

• 2 Bay Area Storm-Related Deaths Reported
• Landslide That Trapped Residents, Triggered Evacuations, Monitored As Rain Falls
• Home Slides Into Russian River In Forestville
• WATCH: Terrifying Close Call As Woman Rescued From Flooded Car