December Deluge Delivers Even More Rain and Mess Than Promised

Update, 9:25 p.m. Thursday: The drying out starts ... now.

The storm that swamped the Bay Area and prompted flash flood warnings, inundated roads and triggered rock and mud slides from Sonoma County into Monterey County has moved south. After a few showers late Thursday and early Friday, the region is in for what appears to be at least a week of non-rain.

The torrents of rain -- which brought anywhere from an inch to nearly 3 inches of rain in most valley and bayside locations while soaking hills and ridges with between 5 and 7 inches since the storm's onset late Wednesday -- caused rapid rises on the Russian and Napa rivers and brought both streams to near flood stage.

In Marin County, several creeks briefly surged past flood stage, prompting warnings and an evacuation of downtown San Anselmo. Creeks also rose out of their banks in several locations in Santa Rosa and Petaluma in Sonoma County.

Gusty winds buffeted the region's higher terrain most of the day. The National Weather Service reported gusts hitting 50 mph or more in every Bay Area county except San Francisco, which recorded gusts in the 30-mph range.

The heavy rain and high winds caused the cancellation of about 90 flights into and out of San Francisco International Airport. Oakland and San Jose airports reported no cancellations.

The storm leaves most of Northern California well above normal for rainfall this season. North State reservoirs are showing the effects of our copious fall rains, with virtually every major reservoir at levels that are well above average for mid-December. We'll offer some of that data on Friday

The departing storm will be followed by an extended period of dry -- and initially cold -- weather.

Lows in some of the Bay Area valleys could fall into the 20s over the weekend. Highs will range from the upper 40s to the low 50s.

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Update, 1:30 p.m. Thursday: If you've been out on the road or looking out a window anywhere in the vicinity of San Francisco, you know it's raining. If you've been confined to an isolation tank, let us provide some details about the outdoor proceedings.

The heavy rain that weather models forecast would pound the Bay Area has arrived in Marin, Sonoma and Napa counties with a vengeance and is continuing its very slow progress to the south.

Just before 1 p.m., the continuing deluge prompted the National Weather Service to issue a flash flood warning for southeastern Sonoma and northern Marin counties. Specifics about the warned areas, per the weather service:

Automated stream gauges have reported water levels rising above flood stage on Willow Brook in Penngrove Park in Petaluma, Sonoma Creek at Agua Caliente, Copeland Creek in Rohnert Park, Colgan Creek near Sebastopol, and other creeks in the lower Laguna de Santa Rosa west of the city of Santa Rosa. There have also been reports of flooding in other lowland valley settings in southern Sonoma County and northern Marin County, as well as roadway flooding.

Here's a look at the current weather radar, by way of Weather Underground:

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A rough key to the colors on the map: green means rain is falling; yellow means rain is pounding down; orange means you're wondering where you left your hip waders.

The CHP is reporting numerous instances of flooded highways and freeways, including Interstate 80 in San Francisco at the split with U.S. 101, at several places on 101 in Marin County and in southern Sonoma County at the junction of Highways 37 and 121. The CHP also reported dozens of traffic collisions related to the storm.

As we said earlier, the usual wet locations in northern Sonoma County got a good soaking earlier in the day, with Venado ("The Deer"), west of Healdsburg, recording 4.40 inches of rain between midnight and noon.

Rainfall totals closer to the Golden Gate have risen sharply as the storm system trundles south.

Sonoma County's Charles M. Schulz Airport had gotten 1.60 inches in the six hours ending at noon. A host of rain gauges in the Petaluma area all showed an inch or more in the same period. Kentfield, on the northeastern flank of Mount Tamalpais, picked up 1.26 inches, including a startling .75 between 11 a.m. and noon.

Rainfall totals quickly drop to the south, with just .18 of an inch recorded at San Francisco International Airport, .08 in downtown San Francisco, and .01 at Oakland International and San Jose International.

The Santa Cruz Mountains had also gotten a decent shot of rain by midday, with a gauge in the community of Ben Lomond recording .79 of an inch. Soquel, at the foot of the hills east of Santa Cruz, picked up .91.

The copious North Bay precipitation prompted the National Weather Service to issue an urban and small stream flood advisory through 4:15 p.m.

The storm has prompted a series of high-water advisories from the California-Nevada River Forecast Center. Rivers expected to reach flood state include the Navarro, in Mendocino County, and the lower reaches of the Eel, south of Eureka.

The center said the Russian River at Guerneville will see a steep rise from its current level of 9 feet to 30.7 feet by midday Friday. That will exceed the river's monitor stage -- the level at which forecasters urge nearby residents and authorities to take action to protect property -- but only minor flooding is expected.

Original post, 8 a.m. Thursday: A wet, windy storm continues to crawl down the coast north of San Francisco early Thursday, carrying what forecasters promise will be one of our most intense dousings of the rainy season so far and terrible travel conditions throughout much of the afternoon and evening.

The storm, fed by a relatively rich plume of water vapor originating near the Hawaiian Islands, has been focused for the past day or so on the coast of Northern California and Oregon, where it has dumped torrents of rain.

The storm is also expected to bring lots of rain -- and some snow -- in the Sierra. Heavy rain in the mountains above Yosemite is expected to trigger a rapid rise on the Merced River in Yosemite National Park, possibly closing roads in Yosemite Valley late Thursday and Friday.

By late Wednesday into early Thursday, the heavy rain had made its way as far south as northern Sonoma County. Venado, the famously wet hillside location west of Healdsburg, got 4.60 inches between 7 p.m. Wednesday and 7 a.m. Thursday. More sheltered sites, like Charles M. Schulz Sonoma County Airport just outside Santa Rosa, got just .29 of an inch during the same period.

The National Weather Service says the heaviest rain is expected to reach the Golden Gate by noon, and the storm will move slowly south, sweeping through the Santa Clara Valley late in the afternoon.

The potential for a transportation mess moved one National Weather Service forecaster to write Wednesday, "The main front will work its way through the heart of the Bay Area during the afternoon and evening hours of Thursday setting the stage for a horrendous afternoon commute. ..."

"Horrendous." Not a word you see much in NWS communications.

The National Weather Service forecasts the storm, which had reached central Sonoma County in time for the morning commute, would bring between 1 to 2 inches of rain to most bayside and valley locations by midnight. Coastal hills and mountains will see a lot more rain -- 5 inches or more, the NWS says.

That's the story on the rain. The storm is expected to be very windy, too.

Forecasters have issued a wind advisory for the Bay Area warning of sustained winds of 25 to 35 mph with gusts of 50 mph in higher terrain late Thursday afternoon until late in the evening.

The predicted deluge, which coincides with unusually high tides, also threatens widespread flooding of roadways near the bay, including U.S. 101 in Marin and San Mateo counties.

The heavy rain has triggered rapid rises on both small coastal rivers that are quick to rise and fall and on Northern California's mother river, the Sacramento.

The California-Nevada River Forecast Center is forecasting brief flooding on the Navarro River in Mendocino County and the Eel in Humboldt County.

The center forecasts high water at several locations on the Sacramento between Red Bluff and the state capital. The rising river will flow into bypass channels created to ease pressure on the river's levee system.

Rain totals for the 24 hours ending 7 a.m. Thursday ranged from 5 to nearly 7 inches in the wettest locations of northwestern California, including 6.80 inches at Honeydew and 6.34 at Cooskie Mountain in Humboldt County.

Rain is forecast to end in most Bay Area locations by early Friday, to be followed by colder and clearing weather. Lows in some of the region's valley locations could fall into the 20s over the weekend.

The outlook for the coming week, forecasters say, is dry.