An Atmospheric River event brought heavy rain and gusty winds with a strong winter storm that impacted the Bay Area for several days in mid-December. Cyclogenesis occurred with a 979 mb low forming off the Northern California coast. On December 11, the intense surface low moved up the coast and drug a narrow cold frontal rainband (NCFR) through the Bay Area that morning and early afternoon. NCFRs are rapidly moving fronts that are notorious for intense rainfall and gusty winds despite having limited instability.
The NCFR wasn't a major wind producer, but the rainfall rates were impressive. Instantaneous rainfall rates of 1.5-2 inches/hr were reported. Observational data from the Big Sur Coast were also impressive with Big Sur receiving 4.43 in 2 hours and Flores Camp receiving 3 in 1 hour. It wasn't so much the total amount of rainfall for many locations, but the intensity and how much was received in a short amount of time.
Many locations around the entire Bay Area had flooding: urban flooding of streets and highways, flooding of creeks and even one large river in the North Bay. Eventually the NCFR slowed around the Big Sur Coast. The stalling was likely due to another 'wave' in the atmosphere, farther to the southwest, riding along the boundary. The end result was to have the weakened NCFR lift back northward, almost like a quasi-warm front, producing another round of moderate to locally heavy rainfall around the Bay Area, compounding flooding concerns.
In addition to the impressive rainfall, winds also became a problem for the water soaked ground, drought stressed trees and diseased trees. Peak winds occurred over the higher terrain with the Lick Observatory reporting 83 mph. Most low elevation areas saw much lower wind speeds.
Lastly, the intense winds over the coastal waters helped to generate a fresh swell that produced very dangerous surf with large breaking waves. The Big Sur Coast buoy reported a peak wave of 19.7 feet.
The event was followed by several weaker storm systems that week that brought additional rainfall, continued flooding and mudslide concerns to the area.

Flash Flood in SAN MATEO, CALIFORNIA
From 11-DEC-14 08:00:00 to 11-DEC-14 08:00:00 (PST-8)
Location: SAN BRUNO
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Public

Significant flash flooding on Interstate 280 was reported by the public. This coincided with a nearby observation of 0.90 of rainfall in 30 minutes at San Bruno Mountain. Traffic was significantly impacted and slowed or stopped during the height of morning rush hour.

Flash Flood in ALAMEDA, CALIFORNIA
From 11-DEC-14 08:33:00 to 11-DEC-14 08:33:00 (PST-8)
Location: EMERYVILLE
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

California Highway Patrol observed 18 inches of water on roadway on WestBound Interstate 580 to Eastbound Route 24.

Flash Flood in MARIN, CALIFORNIA
From 11-DEC-14 08:33:00 to 11-DEC-14 08:33:00 (PST-8)
Location: OLEMA
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Public

Flooding from Pt. Reyes to Olema on Highway 1. Campground flooded.

Flash Flood in SAN MATEO, CALIFORNIA
From 11-DEC-14 08:50:00 to 11-DEC-14 08:50:00 (PST-8)
Location: PEDRO VLY
Flood cause: Heavy Rain
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Public

Public reports water covering roadway and parking lots along San Pedro Creek.

Flash Flood in SONOMA, CALIFORNIA
From 11-DEC-14 10:20:00 to 11-DEC-14 10:20:00 (PST-8)
Location: HEALDSBURG
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Public

Flash flood swept SUV off road and into Dry Creek.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 02:00:00 to 11-DEC-14 02:00:00 (PST-8)
Location: WINDSOR
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Northbound US-101 flooded across all lanes, north of Arata Lane.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 04:29:00 to 11-DEC-14 04:29:00 (PST-8)
Location: WILFRED
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Significant amount of water across area roadways near Laguna de Santa Rosa.

Flood in MARIN, CALIFORNIA
From 11-DEC-14 04:30:00 to 11-DEC-14 04:30:00 (PST-8)
Location: GREEN BRAE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flooding on all lanes of Northbound US-101 at Lucky Drive.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 05:18:00 to 11-DEC-14 05:18:00 (PST-8)
Location: HEALDSBURG
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Foss Creek over banks and flooding Vine and Grove. Law enforcement closed roads.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 07:11:00 to 11-DEC-14 07:11:00 (PST-8)
Location: MARK WEST
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Standing water causing roadway flooding in Healdsburg.

Flood in NAPA, CALIFORNIA
From 11-DEC-14 07:23:00 to 11-DEC-14 07:23:00 (PST-8)
Location: WEST NAPA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water flooding all lanes of Route 29 near Napa.

Flood in MONTEREY, CALIFORNIA
From 11-DEC-14 12:29:00 to 11-DEC-14 12:29:00 (PST-8)
Location: MOSS LNDG
Flood cause: Heavy Rain
Property damage: 1.50K
Crop damage: 0.00K
Reported by: Law Enforcement

Roadway flooding at Mojo Cojo Slough on Moss Landing.

Flood in SANTA CLARA, CALIFORNIA
From 11-DEC-14 12:47:00 to 11-DEC-14 12:47:00 (PST-8)
Location: COYOTE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Roadway flooding on Southbound US-101 at 85.

Flood in SANTA CLARA, CALIFORNIA
From 11-DEC-14 13:05:00 to 11-DEC-14 13:05:00 (PST-8)
Location: BURBANK
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

CHP reports water 1 foot deep covering almost entire Parkmoor Onramp to Interstate 280 Soutbound.

Flood in MONTEREY, CALIFORNIA
From 11-DEC-14 13:15:00 to 11-DEC-14 13:15:00 (PST-8)
Location: MOSS LNDG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Roadway flooding reported at intersection of Highway 1 and Struve Road.

Flood in MONTEREY, CALIFORNIA
From 11-DEC-14 14:06:00 to 11-DEC-14 14:06:00 (PST-8)
Location: PRUNEDALE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Roadway flooding reported from intersection of Meridian Road and Archer Road.

Flood in ALAMEDA, CALIFORNIA
From 11-DEC-14 15:15:00 to 11-DEC-14 15:15:00 (PST-8)
Location: BAUMBERG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Multiple lanes of CA-92 blocked due to flooding, west of Interstate 880.

Flood in ALAMEDA, CALIFORNIA
From 11-DEC-14 15:15:00 to 11-DEC-14 15:15:00 (PST-8)
Location: EMERYVILLE
Flood cause: Heavy Rain
Property damage: 45.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Ashby Avenue Railway underpass near I-80 is flooded. Three cars are stranded and floating in floodwaters.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 15:15:00 to 11-DEC-14 15:15:00 (PST-8)
Location: BELLEVUE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Parking lots of Elsie Allen High School flooded.

Flood in MARIN, CALIFORNIA
From 11-DEC-14 16:53:00 to 11-DEC-14 16:53:00 (PST-8)
Location: MARIN CITY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Highway 1 flooded and closed from Panoramic Highway to Muir Woods Road.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 18:54:00 to 11-DEC-14 18:54:00 (PST-8)
Location: SCHELLVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

CA-121 flooded at Schellville due to Schell Creek.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 18:54:00 to 11-DEC-14 18:54:00 (PST-8)
Location: JIMTOWN
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Russian River flooded and resulted in closure of CA-128 between Canyon Road and Alexander Valley Road including Geyserville.

Flood in MONTEREY, CALIFORNIA
From 11-DEC-14 19:30:00 to 11-DEC-14 19:30:00 (PST-8)
Location: SANTA RITA
Flood cause: Heavy Rain
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Other Federal Agency

Fifteen homes were flooded and damaged due to flooding from Santa Rita Creek along Russel Road in Salinas.

Flood in SAN MATEO, CALIFORNIA
From 11-DEC-14 22:30:00 to 11-DEC-14 22:30:00 (PST-8)
Location: EAST PALO ALTO
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

US-101 closed in both directions due to flooding in Menlo Park between Willow and Marsh exits.

Heavy Rain in SONOMA, CALIFORNIA
From 11-DEC-14 03:20:00 to 11-DEC-14 03:20:00 (PST-8)
Location: CLOVERDALE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Rainfall totals of 4.5 inches so far, with 2.5 inches since midnight.

Heavy Rain in SONOMA, CALIFORNIA
From 11-DEC-14 08:09:00 to 11-DEC-14 08:09:00 (PST-8)
Location: OCCIDENTAL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter measures rainfall total from 5:00 PM December 10  through 7:30 AM December 11 of 3.97 inches.

Heavy Rain in MONTEREY, CALIFORNIA
From 11-DEC-14 10:06:00 to 11-DEC-14 10:06:00 (PST-8)
Location: (MRY)MONTEREY ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Other Federal Agency

A large number of boats in Monterey Harbor had to be pumped out to avoid sinking on December 11 due to heavy rainfall.

Heavy Rain in SONOMA, CALIFORNIA
From 11-DEC-14 13:22:00 to 11-DEC-14 13:22:00 (PST-8)
Location: SKAGGS SPGS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

The Venado gauge in Northern Sonoma County measured a 24 hour rainfall of 9 inches.

Heavy Rain in SANTA CLARA, CALIFORNIA
From 11-DEC-14 16:53:00 to 11-DEC-14 16:53:00 (PST-8)
Location: EVERGREEN
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Heavy rainfall resulted in the partial roof collapse of a Grocery Store in San Jose.

Heavy Rain in MONTEREY, CALIFORNIA
From 11-DEC-14 19:30:00 to 11-DEC-14 19:30:00 (PST-8)
Location: CASTROVILLE
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Other Federal Agency

Heavy rain overwhelmed the sewage plant in Castroville resulting in a sewage spill.

Flash Flood in SAN MATEO, CALIFORNIA
From 11-DEC-14 10:00:00 to 11-DEC-14 10:00:00 (PST-8)
Location: ATHERTON
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Heavy rain caused flooding of several trailer parks in Redwood City. The combination of standing water and a local creek flooding resulted in the need for residents to be evacuated from the Le Mar Trailer Park and RC Mobile Home Park on E Bayshore in Redwood City. 50 mobile homes were evacuated and residents were sent to shelters.

Flash Flood in MARIN, CALIFORNIA
From 11-DEC-14 09:00:00 to 11-DEC-14 09:00:00 (PST-8)
Location: NOVATO
Flood cause: Heavy Rain
Property damage: 4.00M
Crop damage: 0.00K
Reported by: Broadcast Media

Heavy rainfall produced significant rises on Novato Creek between highways 101 and 37 on the east side of the city of Novato. This led to an intentional breach of the levee on a 20 foot section to prevent floodwaters from reaching downtown businesses and nearby subdivisions. This same flooding also resulted in failure of a smaller portion of the levee and overtopped another section. Caltrans levees on highway 37 were breached and a culvert was washed out.

Debris Flow in MARIN, CALIFORNIA
From 11-DEC-14 10:00:00 to 11-DEC-14 10:00:00 (PST-8)
Location: TAMALPAIS VLY
Flood cause: Heavy Rain
Property damage: 1.00M
Crop damage: 0.00K
Reported by: Broadcast Media

A slide under sixty feet of Highway 1 near Muir Beach resulted in a full closure of the road which is expected to last for several months.

Debris Flow in MARIN, CALIFORNIA
From 11-DEC-14 10:00:00 to 11-DEC-14 10:00:00 (PST-8)
Location: MARIN CITY
Flood cause: Heavy Rain
Property damage: 1.00M
Crop damage: 0.00K
Reported by: Broadcast Media

A significant mudslide occurred along Tennessee Valley Road.

Strong Wind in SAN FRANCISCO, CALIFORNIA
From 11-DEC-14 11:00:00 to 11-DEC-14 11:00:00 (PST-8)
Magnitude: 39.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Utility Company

Downed trees and power lines in San Francisco resulted in outages impacting up to 95,000 customers.

Flash Flood in SAN FRANCISCO, CALIFORNIA
From 11-DEC-14 08:22:00 to 11-DEC-14 08:22:00 (PST-8)
Location: OCEAN VIEW
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

San Bruno BART station closed during rush hour commute due to flooding of station from heavy rain.

Coastal Flood in SAN FRANCISCO, CALIFORNIA
From 11-DEC-14 07:30:00 to 11-DEC-14 07:30:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Elevated water levels, strong winds, and swell produced water that flooded over the wall on the Embarcadero and resulted in the road being closed for several hours.

Strong Wind in NORTHERN MONTEREY BAY, CALIFORNIA
From 11-DEC-14 08:30:00 to 11-DEC-14 08:30:00 (PST-8)
Magnitude: 39.00 EG
Property damage: 1.50K
Crop damage: 0.00K
Reported by: Broadcast Media

Strong wind gusts blew down an 80 foot cypress tree at Gateway School in Santa Cruz into an area where children were congregating outside waiting for school to begin. The tree crushed a picnic table and fell on an 11 year old boy and girl. The girl sustained minor injuries. The boy's arm and shoulder were pinned by the tree and he broke his arm and had to have rescuers cut the tree apart to free him.

Strong Wind in SANTA CRUZ MOUNTAINS, CALIFORNIA
From 11-DEC-14 09:00:00 to 11-DEC-14 09:00:00 (PST-8)
Magnitude: 48.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Five vehicles were crushed when a redwood tree was blown down across them.

Flood in MONTEREY, CALIFORNIA
From 11-DEC-14 20:00:00 to 11-DEC-14 20:00:00 (PST-8)
Location: MOSS LNDG
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Moro Cojo Slough backed up and flooded homes and roadway along its banks. Sandbagging operations were needed to protect the homes from significant damage. The slough flooded from heavy rain and then the flap gates were damaged and could not properly drain the slough into Moss Landing Harbor.

High Wind in EAST BAY HILLS AND THE DIABLO RANGE, CALIFORNIA
From 11-DEC-14 07:18:00 to 11-DEC-14 07:18:00 (PST-8)
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

Measured gust of 64 MPH on Calaveras Road.

High Wind in EAST BAY HILLS AND THE DIABLO RANGE, CALIFORNIA
From 11-DEC-14 04:00:00 to 11-DEC-14 04:00:00 (PST-8)
Magnitude: 59.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

A measured gust of 68 MPH on Mt. Diablo.

High Wind in NORTH BAY MOUNTAINS, CALIFORNIA
From 11-DEC-14 06:51:00 to 11-DEC-14 06:51:00 (PST-8)
Magnitude: 62.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

Measured gust of 71 MPH at Woodacre.

High Wind in SANTA LUCIA MOUNTAINS AND LOS PADRES NATIONAL FOREST, CALIFORNIA
From 11-DEC-14 16:40:00 to 11-DEC-14 16:40:00 (PST-8)
Magnitude: 58.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

A measured gust of 67 MPH at Highlands Peak.

High Wind in SANTA CRUZ MOUNTAINS, CALIFORNIA
From 11-DEC-14 08:32:00 to 11-DEC-14 08:32:00 (PST-8)
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

Wind gust of 64 MPH measured at Los Gatos.

High Wind in EAST BAY HILLS AND THE DIABLO RANGE, CALIFORNIA
From 11-DEC-14 07:30:00 to 11-DEC-14 07:30:00 (PST-8)
Magnitude: 72.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

A wind gust of 83 MPH was measured atop Mt. Hamilton at the Lick Observatory weather station.

Flood in SONOMA, CALIFORNIA
From 11-DEC-14 06:25:00 to 11-DEC-14 06:25:00 (PST-8)
Location: HEALDSBURG
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reports numerous road closures due to flooding in Healdsburg. Intersections included Piper at East, Center at Grant, Piper at Healdsburg, and Center at Mitchell.

Heavy Rain in SONOMA, CALIFORNIA
From 11-DEC-14 11:18:00 to 11-DEC-14 11:18:00 (PST-8)
Location: CLOVERDALE MUNI ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter has measured 4.19 inches of rainfall since midnight and a storm total of six inches so far.