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.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SGX wrote it up.
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.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Diego, CA wrote its last area forecast discussion before the first event at Dec 21, 9:30 PM PST, 1 hour 50 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Thu Dec 21 2023
.SYNOPSIS...
Showers and isolated thunderstorms will spread over land overnight
and produce locally heavy rain, continuing through Friday. Snow will
fall in the highest mountains late today and Friday. The
precipitation will gradually weaken Friday night and Saturday
morning with fair warmer weather prevailing during the early and
middle of next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Thunderstorms have been occurring since late this afternoon over the
coastal waters, and they spread into far northern San Diego and
Orange County for awhile early this evening. At 9 PM, the activity
was mostly off the coast where surface-based CAPE values were almost
up to 1500 J/kg. Latest HRRR update shows some delay from previous
runs with activity becoming widespread over San Diego County mostly
after midnight and spreading north through the rest of our forecast
area a few hours later due to a wave circulating around the upper
low to our west. However, latest radar shows convective cells now
moving into far SW San Diego County. Locally heavy rainfall rates of
0.5" per hour or more will occur with some of these heavier
showers/thunderstorms. After that wave moves through, the
instability of the cold core low will continue the thunderstorm risk
through Friday, though with the track of the low going just to the
south of San Diego, the biggest threat of thunderstorms will in
northern Baja and also out towards the deserts of SoCal.
From previous discussion...
The low pressure system that will bring us widespread, heavy
rainfall is roughly 400 miles west of San Diego this afternoon. Mid-
level water vapor imagery is showing a moisture plume from that low
has moved into LA county this afternoon, producing showers and
isolated thunderstorms. That moisture is forecast to move south and
start to impact Orange County this evening. Moisture will continue
to spread south overnight, impacting San Diego County around
midnight. The low is expected to move further south and east Friday.
The southeasterly movement of the system will allow for wrap around
moisture to impact the deserts and desert mountain slopes of the San
Diego and Riverside County mountains much of the day Friday. The low
will continue to quickly trek east overnight Friday, reaching the
Four Corners region by Saturday morning. See Hydrology section for
more details on amounts, rates and flooding potential.
Snow levels will remain around 7500 feet through most of the storm.
As the cold core moves through the region and begins to exit, snow
levels drop briefly to 6000-6500 feet Friday night, but only a few
inches of snow is expected to accumulate below 7000 feet. Much of
the snowfall is expected at and above 8000 feet. Wind will pick up
this evening with the main wave moving through, but this storm is
not a big wind maker. Easterly winds appear strongest in the High
Desert and mountains, and below the San Gorgonio Pass in the Inland
Empire, where top gusts should reach 30-40 mph. Wind gusts along the
coast and in the coastal waters could reach 20-30 mph.
After the lingering showers end Saturday, dry weather will prevail
into early next week. There will continue to be some clouds west of
the mountains with residual moisture through Sunday. A gradual
warming trend is expected early next week due to some weak offshore
flow and a ridge aloft. Highs Monday through Wednesday should get
into the upper 60s and lower 70s at lower elevations. Late next week
the jet stream is showing signs of potentially dipping southward
again, which could bring more wet weather to the area.
&&
.AVIATION...
220430Z...Coast/Valleys/Mountains...Isolated SHRA/TSRA with
occasional CIGs 1,500-2,000 ft MSL expected as the storm system
impacts the area west of the coastal mountains. Heaviest
precipitation is expected to occur around 09Z-15Z Friday, with
widespread SHRA/TSRA and CIGs 1,500-2000 ft MSL and VIS 1-2SM during
showers. Coastal mountain slopes obscd in clouds and pcpn.
Deserts...SCT-BKN080-100 through this evening. Aft 09Z Fri, BKN-
OVC015-025 obscuring higher terrain of the desert slopes.
&&
.MARINE...
South winds of 15-20 knots gusting to 25 knots along with combined
seas of 5-8 feet in choppy conditions will produce hazardous
conditions for small craft through tonight. Isolated showers through
this evening then widespread showers and isolated thunderstorms
tonight into Friday. Any thunderstorms that develop could produce
locally gusty, erratic winds, locally hazardous seas, lightning and
waterspouts. No hazardous marine conditions are expected Friday
night through Monday.
&&
.BEACHES...
There is a chance for lightning at the beaches tonight and Friday.
A west-northwest swell with a 12-13 second period will produce surf
of 3-5 ft and strong rip currents at the west-facing beaches of San
Diego County through this afternoon. &&
.HYDROLOGY...
Areas of heavy rain and embedded thunderstorms are expected through
the entire region tonight into Friday. Rain rates between 0.50-1
inch per hour, expected with rates towards the higher end of the
spectrum where thunderstorms develop. Orographic effects tonight
into early Friday will occur mainly on the south-facing slopes of
the San Bernardino County Mountains. That will shift late Friday
morning with better orographic enhancement on the east-facing slopes
of the Riverside/San Diego County Mountains. Periods of heavy rain
expected late tonight into Friday afternoon for areas west of the
mountains, particularly for coastal areas. Periods of heavy rain
most likely during the day Friday, potentially into the early
evening hours, for the deserts and desert mountain slopes. Forecast
rainfall totals through Saturday currently look to be 0.75-1.75
inches for the coast and valleys, 1-2 inches for the mountains, and
about 0.50-1.25 inches for the deserts. The San Diego deserts and
Coachella Valley are more likely to see rainfall totals at the
higher end of the aforementioned range for the deserts. Flooding is
possible anywhere in the region. Plan on impacts from flooding
impacting the Friday commute.
Both the San Diego River and the Santa Margarita Rivers are forecast
to remain below monitor stage. The San Diego River is expected to
peak at 6.6 feet and the Santa Margarita river is expected to peak
at 7.8 feet Friday evening. Showers will end Saturday, with some
lingering light showers in the mountains and valleys Saturday
morning.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from 6 PM PST this evening through Friday evening
for Apple and Lucerne Valleys-Coachella Valley-Orange
County Coastal Areas-Orange County Inland Areas-Riverside
County Mountains-San Bernardino County Mountains-San
Bernardino and Riverside County Valleys-The Inland Empire-
San Diego County Coastal Areas-San Diego County Deserts-San
Diego County Mountains-San Diego County Valleys-San
Gorgonio Pass Near Banning-Santa Ana Mountains and
Foothills.
Winter Weather Advisory from 6 PM this evening to 4 AM PST
Saturday for Riverside County Mountains-San Bernardino
County Mountains.
PZ...Small Craft Advisory until 2 AM PST Friday for Coastal Waters
from San Mateo Point to the Mexican Border and out to 30 nm-
Waters from San Mateo Point to the Mexican Border Extending
30 to 60 nm out including San Clemente Island.
&&
PUBLIC/HYDROLOGY...Maxwell (Update)/CO (Previous Discussion)
AVIATION/MARINE/BEACHES...PG/SukThe San Diego radar (KNKX), 45 km away, was scanning. The volume nearest the first event began at 07:22 UTC.
4 flood, 2 flash flood, 1 lightning, 1 thunderstorm wind. Local standard time, as filed.
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 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.
California Highway Patrol reported flooding at SR-62 and Yucca Park with water flowing down the Morongo Grade.
All lanes of I-10 Eastbound were flooded just west of Pepper Ave.
I-15 offramp to Main Street was closed due to flooding.
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.
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.
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.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyWarnings in California, December 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1152642, 1152643, 1152636, 1152637, 1152638, 1152639, 1152640, 1152667.