Parade Of Storms To Douse NorCal With Heavy Rain: What To Know

SAN FRANCISCO, CA — A parade of storms are headed for much of the Golden State this week, first arriving in Northern California before bringing rain to the bone-dry and fire-scarred Southland.

In NorCal, millions of people across 11 counties will soon fall under a flood watch until early Tuesday morning ahead of the expected downpour, according to the National Weather Service.

"Light rain has moved into far northern Sonoma County late this morning. Look for more widespread rainfall to gradually shift south throughout the day into tonight, along with strong winds persisting through Tuesday," forecasters said Monday just before 11 a.m.

While an atmospheric river system had already brought light showers to the northern reaches of the state on Monday, a second, stronger system is set to hit Tuesday before a third, lighter system arrives later in the week.

Through midweek, the second atmospheric river storm is expected to douse much of Northern California with moderate to heavy rain with hefty snow expected in the Sierra Nevada before that system weakens and takes aim at Southern California, where two storm systems are expected to hit, according to the National Weather Service.

Through Friday, the North Bay could get between 3 and 6 inches of rain, while areas of higher terrain could see 6 to 8 inches. Meanwhile, much of the Bay Area could get 2 to 4 inches of rain, according to the San Francisco Bay Area NWS office.

Predicted rain totals:

• San Francisco: 3 to 4 inches
• Livermore: 2 to 3 inches
• Concord: 2 to 3 inches
• Napa: 3 to 4 inches
• Santa Rosa: 3 to 4 inches
• Santa Cruz: 4 to 6 inches

Much of the Bay Area saw rain over the weekend, but heavier downpours on the way could cause flooding in some areas. A slight risk of excessive rainfall could persist in NorCal into Tuesday, prompting flooding concerns for San Francisco.

"Those living in areas prone to flooding should be prepared to take action should flooding develop," NWS forecasters wrote on Monday.

"Our biggest concerns are flooding of creeks and streams and an increased risk for downed trees due to the combination of wind and moist soils," forecasters said.

Strong winds were also expected to hammer the area during the storms, which could cause power outages and road hazards, officials warned.

"If you need to prep for the incoming storm do it now. Rain and gusty winds are on the way. Double check the gutters, storm drainages, weakened branches, etc.," Bay Area NWS forecasters wrote on Monday.

The third atmospheric river is expected to hit Thursday and Friday, but it is predicted to be much weaker and pointed farther south. Temperatures are expected to turn cold again, especially in the mornings. Going into the weekend, temperatures are expected to drop "significantly," forecasters said.

The news comes after 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, which tends to tilt the odds toward dryer than normal in SoCal and wetter than average weather in NorCal.

But La Niña isn't predicted to last long this year, experts told the San Francisco Chronicle.

“El Niño and La Niña events typically peak in the early winter and decline in strength into the spring, so there just isn’t much time for this event to develop further,” Emily Becker, an associate director of the University of Miami Cooperative Institute for Marine and Atmospheric Studies, told the newspaper.