A strong area of low pressure off the California coast brought heavy rain and thunderstorms to Southern California on December 21st. The biggest impact was a microburst near the Carlsbad Airport, where a wind gust of 48 knots/55 mph was measured via ASOS. Signs at the airport were damaged in additional to several other reports of tree damage nearby. Several reports of street and flash flooding were also received across areas from the coast to as far east as Anza-Borrego State Park.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 22-DEC-23 02:15:00 to 22-DEC-23 03:15:00 (PST-8)
Location: YUCCA VLY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

California Highway Patrol reported flooding at SR-62 and Yucca Park with water flowing down the Morongo Grade.

Flood in SAN BERNARDINO, CALIFORNIA
From 22-DEC-23 02:30:00 to 22-DEC-23 03:30:00 (PST-8)
Location: COLTON ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

All lanes of I-10 Eastbound were flooded just west of Pepper Ave.

Flood in SAN BERNARDINO, CALIFORNIA
From 22-DEC-23 03:15:00 to 22-DEC-23 04:15:00 (PST-8)
Location: THORN
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

I-15 offramp to Main Street was closed due to flooding.

Flood in SAN DIEGO, CALIFORNIA
From 22-DEC-23 12:30:00 to 22-DEC-23 13:30:00 (PST-8)
Location: DESERT LODGE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

One of four crossings in Anza Borrego State Park had fast-flowing water, making it unpassable. Anza Borrego Research shared video of Coyote Creek flooding.

Flood in SAN DIEGO, CALIFORNIA
From 22-DEC-23 13:00:00 to 22-DEC-23 14:00:00 (PST-8)
Location: BORREGO SPGS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Coyote Creek overflowed a low water crossing along a dirt road in Anza-Borrego State Park. This occurred suddenly after the rain had ended. Time of event is estimated from radar.

Lightning in SAN DIEGO, CALIFORNIA
From 21-DEC-23 23:20:00 to 21-DEC-23 23:40:00 (PST-8)
Location: SAN LUIS REY
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Public

Lightning snapped a large tree about two thirds of the way down near the base. Photo             received via Facebook of a tree near intersection of Douglas Dr and River Rd. This occurred during a line of storms moving through Oceanside around 11:30pm.

Thunderstorm Wind in SAN DIEGO, CALIFORNIA
From 21-DEC-23 23:20:00 to 21-DEC-23 23:40:00 (PST-8)
Location: (CRQ)PALOMAR ARPT CA
Magnitude: 48.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Thunderstorm microburst southwest (shift from the east) wind gust to 55 mph        recorded via the ASOS at KCRQ (Carlsbad-Palomar Airport) at 11:30 pm on December 21. Survey found a dozen trees downed, including a uprooted 3 foot wide eucalyptus tree, an uprooted 2 foot wide pine, and snapped 18 inch pepper tree. Many large branches and tops of trees were snapped off. Tree damage on both north and south sides of the CRQ airport which is on Palomar road, and most trees laying to the east. Yarrow, Kellogg, El Camino, Faraday, Camino Vida Roble and Corte Del Nogal roads affected. Airport reported a sign damaged near the tower.

Flash Flood in RIVERSIDE, CALIFORNIA
From 22-DEC-23 14:45:00 to 22-DEC-23 15:45:00 (PST-8)
Location: RIMLON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Number 3 and 4 lanes of I-10W near and east of Date Palm Drive blocked with mud and debris. The nearby Thousand Palms mesonet recorded 0.83 inch of rain since 3 AM that morning, though no rain was occurring when the flooding was reported.