Atmospheric River Arrives: Napa County Under Flood Watch

NAPA COUNTY, CA — Napans were urged to be prepared as an atmospheric river storm began bearing down Thursday on Napa County and the Bay Area and is expected to last into Friday, bringing floods and thunderstorm hazards.

A flood watch was implemented for the entire region from Thursday afternoon until Sunday morning. A wind advisory was expected to remain in effect until Friday afternoon.

Gov. Gavin Newsom declared a state of emergency to support storm response in 21 counties, including Napa. Sonoma County was among 13 counties last week where a state of emergency was already declared.

"Widespread wetting rains are expected over the district through Friday as a potent atmospheric river moves over California," the weather service said. "The moderate to heavy rain will bring increased flooding concerns and landslide potential. In addition to the rain, gusty southerly winds will persist through Friday. Winds will be strongest near the coast and higher terrain."

Most cities in the Bay Area observed at least a tenth of an inch of rain in the past 24 hours, as of 4 p.m. Thursday. The North Bay has seen the most rainfall, with many cities observing more than half an inch of rain.

At 6 p.m. Thursday, the National Weather Service reported the following 12-hour rainfall totals for Napa County: Yountville, 1.64 inches; Napa Justin-Siena High School, 1.63 inches; Calistoga, 1.32 inches; Saint Helena, 1.06 inches; Rockville, 1.15 inches; Angwin, 1.02 inches; Pope Valley, 0.93 inches; Atlas Peak, 0.86 inches; Northeast Napa, 0.80 inches; Napa County Airport, 0.67 inches; American Canyon, 0.52 inches.

Flooding Reported On Napa County Roadways

As of 8 p.m. Thursday, California Highway Patrol and the Napa County Sheriff's Office reported the closure of northbound state Highway 29 (Sonoma Boulevard) between Green Island Road and South Kelly Road. Traffic was being diverted at Paoli Loop Road.

Flooding was also reported Thursday evening on state Highway 121 at Duhig Road and on state Highway 29 at Oakville Grade Road.

At 8:29 p.m. Thursday, boulders were reported on Silverado Trail North at Madrone Knoll Way.

Flooding prompted a road closure at 7:52 p.m. Thursday at state Highways 121 and 116 in Sonoma County. Two cars were reportedly stuck in the water which was described as a river across the roadway.

Napa River Flooding Potential

According to the National Weather Service, rainfall and snowmelt will lead to rapid rises of area rivers, streams, and creeks. Rivers with the most significant flooding potential are Napa, Russian, Salinas, Pajaro and Carmel.

The Napa River near Napa was forecast to reach "monitor stage" of 22 feet Friday morning. The river's flood stage is 25 feet. The current forecast Thursday afternoon indicated the river would crest at 22.1 feet Friday afternoon, according to the California Nevada River Forecast Center.

In preparation for possible flooding, the city of Napa on Thursday closed the Oxbow flood gates along the Napa River at McKinstry street.

In neighboring Sonoma County, the Russian River was forecast to reach the "monitor stage" of 29 feet Friday afternoon. The river's flood stage is 32 feet. The current forecast indicates the river will crest at 30.9 feet Friday night at Johnson's Beach near Guerneville. Thursday afternoon, the river was at 12.6 feet.

"Flooding is an extremely serious concern associated with this AR," the weather service said. "The ground is already saturated and streams/rivers are already swollen. When additional heavy rainfall falls on an already saturated ground the only thing it can do is run off. Streams/rivers will be quicker to flood due to their current capacity."

The Napa County Office of Emergency Services issued the following statement Thursday:

"Napa County is under a flood watch effective Thursday afternoon, March 9 through Sunday morning. This weather event is expected to bring winds, heavy rain, flooding, and increased potential for power outages.

"Due to very saturated soils, even winds on the lower end of the speed range can cause downed trees. When trees fall, this can be a threat to lives, cause power outages, and add debris to our roadways.

"Please continue to exercise caution when on the road. If you see a downed or sagging power line, assume it is energized and extremely dangerous. Do not touch or try to move it, stay clear of the area, call 9-1-1 and PG&E at 1-800-743-5002."

• Visit the readynapacounty website to learn more about how to prepare your household better.
• Keep up to date on the changing weather conditions by visiting the National Weather Services website.
• Keep up to date on any local road closures by visiting Zonehaven: AWARE - Zonehaven
• Keep up to date on any State Road closures by visiting CalTrans: QuickMap (ca.gov)
• Keep up to date on any power outages by visiting PG&E: https://pgealerts.alerts.pge.com/outagecenter/

Sandbag stations are here:

• American Canyon & Milton Road Sandbags
• City of Napa Sandbags
• Wooden Valley & Circle Oaks Sandbags
• Yountville Sandbags
• Dry Creek & Lokoya Sandbags
• St Helena Sandbags
• Angwin Sandbags
• Calistoga Sandbags

This is a developing story; refresh the page for the latest updates.