SANTA ROSA — At least two Sonoma County creeks overflowed their banks early Saturday morning and others were nearing flood stage as a potent Cat. 4 atmospheric river roared into the San Francisco Bay Area.
The plume of tropical moisture came ashore in the North Bay late Friday night and was set to move southward throughout the Bay Area as the day progressed.
The intense downpours from the storm will be falling on already saturated hillsides leading to excessive runoff and the threat of landslides.
Green Valley Creek in Sonoma County continues to rise this morning, despite rainfall rates still less than a 0.1 inches per hour at this time. #SaturatedSoils #CAwx #CAflooding pic.twitter.com/29pctpRjfp
— NWS Bay Area 🌉 (@NWSBayArea) December 31, 2022
Early Saturday morning, the National Weather Service issued flood warnings and flood advisories for communities across the Bay Area.
A Flood Warning was issued for Santa Rosa, Petaluma, Novato, Rohnert Park, Windsor, Healdsburg, Sonoma, Cloverdale, Sebastopol, Cotati, Larkfield-Wikiup, Roseland, South Santa Rosa, Boyes Hot Springs, Black Point-Green Point, Forestville, Guerneville Graton, Occidental and Monte Rio.
“A couple of creeks (Green Valley and Willow Brook) across Sonoma County are already above flood stage, with a couple of more (Santa Rosa and Colgan) above action stage and approaching minor flood,” the weather service reported at 5:20 a.m.
Flood Advisories had been issued for San Francisco and along the Peninsula and also for Napa.
“Another concern on the flooding side of things will be with possible coastal flooding, especially in Marin County,” weather service forecasters warned. “High tide for San Francisco is at 6:26 a.m. which will coincide with the heaviest rain.”
The downpours also created hazardous driving conditions. At 5:47 a.m. CHP officers were responding to more than 40 incidents including accidents, debris slides and roadway flooding.
Fortunately, the storm front should move through the region rather quickly, but will be pretty intense.
“We will receive copious amounts of rain over a a relatively short period of time (1-4 inches over 6-12 hours),” forecasters warned.
Researchers at Scripps Center for Western Weather and Water Extremes predicted Saturday’s atmospheric river will more intense than the one that made landfall on Tuesday. The good news is that current models indicate the heaviest rain will fall between Friday night and late Saturday morning, meaning that the storm shouldn’t impact New Year’s Eve festivities Saturday night.
scripps
The first storm earlier this week dumped nearly five inches of rain on Mt. Tamalpais and also in the Santa Cruz Mountains.
“As this Pineapple Express launches its moisture toward the Bay Area, rain rates will go up,” forecasters said. “That said, the plume of highest moisture will be narrow and intense. Models have varied by numerous miles as to where the head of this stream will initially take aim. Some have it in Mendocino County, while others impact San Mateo County.”
Residents in the North Bay were bracing for the worst from Saturday’s storm.
Tamalpais Valley resident Becky King tells KPIX that she is worried if the drains near her home can handle the heavy rainfall.
“My house is near a creek that rises above my house level. And they try to enforce it every year, but we usually get flooding,” said King. “So, this year I’m a little more concerned.”
Creek levels around the county, like the one near King’s home, are what the Marin County Fire Department will keep a close eye on during this storm.
“Friday and Saturday seem like the bulk of extreme weather will be, so we’ll look at staffing our stations with more people,” said Marin County Fire Deputy Chief Chris Martinelli. “If we see creek levels getting up higher that’s what will trigger us to staff our water rescue resources.”
Of even greater concern is what the next stormy week holds.
“We are in for an extended wet pattern where these saturated soils won’t have time to really dry out,” the weather service said. “The only break we get from rain will happen on Jan 1, but then more rain occur Jan 2-5 with a third moderate atmospheric river moving into our region around Jan 4-5.”
“At this time, the rain totals look to be similar or a little higher than what we saw on Dec 26-27 and what we may see Saturday. Expect several more inches. After Jan 5, it seems light to moderate rain could persist into the second week of January. If that’s the case, then residents across the Bay Area and Central CA need to be aware that additional flooding and shallow mudslides could occur.”
