A low pressure system descended from the Gulf of Alaska southward along the entire Pacific Coast and tapped into sub-tropical moisture originating from the Central Pacific to drop heavy rain throughout the state. A stalled frontal boundary over the Santa Cruz Mountains along with strong southerly winds from a coastal low-level jet, enhanced orographic rainfall over this region, leading to rainfall totals over a 2 day period (Dec 12th-13th) of up to ten inches in the coastal mountains. The stalled boundary was reinvigorated by a secondary boundary bringing in a cold unstable airmass that set off convective showers and lowered snow levels below 2000 ft. A wind advisory, later upgraded to a high wind warning was issued for the southern half of the region from the SF Peninsula down to the Big Sur Coast including the inland zones due to the coastal jet bringing sustained winds up to 40 mph with gusts up to 55 mph. A high surf advisory was issued for the entire coast due to the arrival of a strong NW swell train, along with Gale Warning throughout the coastal waters. A flash flood watch was issued for the Santa Lucia Mountains and Dolan Burn Scar area, where up to 12 inches of rain fell.

Flood in SONOMA, CALIFORNIA
From 13-DEC-21 21:11:00 to 13-DEC-21 22:11:00 (PST-8)
Location: WILFRED
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain caused roadway flooding on Labath Ave.

Flood in ALAMEDA, CALIFORNIA
From 13-DEC-21 05:40:00 to 13-DEC-21 06:40:00 (PST-8)
Location: ALAMEDA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain led to 1 ft of standing water in the roadway.

Flood in SAN MATEO, CALIFORNIA
From 13-DEC-21 08:28:00 to 13-DEC-21 09:28:00 (PST-8)
Location: BAYSHORE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain caused flooding on US101 at S Airport Blvd.

Flood in SAN MATEO, CALIFORNIA
From 13-DEC-21 09:20:00 to 13-DEC-21 10:20:00 (PST-8)
Location: BELMONT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Roadway flooding caused hard closure of SR 92 between SR 35 AND SR1.

Debris Flow in SANTA CRUZ, CALIFORNIA
From 13-DEC-21 10:40:00 to 13-DEC-21 11:40:00 (PST-8)
Location: FOREST PARK
Flood cause: Heavy Rain / Burn Area
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Video, https://www.youtube.com/watch?v=4LFZJqrqidw, of rapid debris flow in Boulder Creek area, 200 ft from where Foreman Creek crosses under SR236. Creek runs through part of the CZU burn scar area.

Flood in MARIN, CALIFORNIA
From 13-DEC-21 07:30:00 to 13-DEC-21 07:50:00 (PST-8)
Location: MARIN CITY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain led to a rockslide on SR1 and partially blocked the road.

Strong Wind in COASTAL NORTH BAY INCLUDING POINT REYES NATIONAL SEASHORE, CALIFORNIA
From 13-DEC-21 13:00:00 to 13-DEC-21 13:30:00 (PST-8)
Magnitude: 29.00 EG
Crop damage: 0.00K
Reported by: Law Enforcement

A tree fell into the roadway and smashed a vehicle at Blackstone Dr. and Heatherstone Dr.

Lightning in MONTEREY, CALIFORNIA
From 13-DEC-21 22:00:00 to 13-DEC-21 23:00:00 (PST-8)
Location: (MRY)MONTEREY ARPT
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A lightning strike blew out a transformer along Del Monte Blvd. Eight power poles fell down but no injuries were reported. https://kion546.com/news/2021/12/14/a-look-at-the-damage-from-the-rain-storm/.

Flood in MONTEREY, CALIFORNIA
From 13-DEC-21 13:07:00 to 13-DEC-21 14:07:00 (PST-8)
Location: NOTLEYS LNDG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Rocks slid onto SR1 and blocked the northbound lane near Bixby Bridge. https://kion546.com/news/2021/12/14/a-look-at-the-damage-from-the-rain-storm/.

Strong Wind in SANTA CLARA VALLEY INCLUDING SAN JOSE, CALIFORNIA
From 13-DEC-21 13:00:00 to 13-DEC-21 13:20:00 (PST-8)
Magnitude: 26.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Strong winds knocked down a power pole at 14680 Shannon Rd. Wires were in the roadway.

Flood in SONOMA, CALIFORNIA
From 13-DEC-21 08:57:00 to 13-DEC-21 09:57:00 (PST-8)
Location: SCHELLVILLE ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain caused flooding and closure of SR 12 between Route 116  and 8th St.