Flood and Heavy Snow in California, March 29 to 30, 2023

Name: Flood and Heavy Snow in California, March 29 to 30, 2023
Start: 2023-03-29T04:00
End: 2023-03-30T16:00
Location: California

March 29 to 30, 2023 · NWS SGX · 5 events in 5 counties and zones

A weak atmospheric river produced widespread moderate rainfall and high-elevation snow across Southern California March 29-30. Several stronger thunderstorm cells occurred across San Diego County, resulting in a Severe Thunderstorm Warning and a Tornado Warning.

Where it happened

Every event with a place to put it; 4 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 5

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.

What happened

The episode as NWS SGX wrote it up.

What forecasters said that day

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 Mar 29, 3:56 AM PST, 4 minutes earlier.

Area forecast discussion, Mar 29, 3:56 AM PST, 4 minutes before

Area Forecast Discussion
National Weather Service San Diego CA
456 AM PDT Wed Mar 29 2023

.SYNOPSIS...
A cold low pressure system moving southward through California
will bring more widespread precipitation today and more showery
precipitation along with a slight chance of thunderstorms for late
tonight into Thursday. Dry and warmer for Friday through the
weekend. Then cooler and windy early next week with a slight
chance for mostly light precipitation as another trough of low
pressure moves inland through the western states.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.SHORT TERM (Today through Friday)...
Satellite imagery shows the center of a cold low pressure system
off the northern California coast early this morning. This system
will move slowly southward today to a position just west of the
Bay Area late in the day. It will move inland across southern
California early Thursday as it weakens.

Precipitation has continued to spread eastward and southward
across southern California overnight and will spread across
southwestern California from the coast to the mountains through
the morning. The precipitation will decrease from the northwest
during the afternoon and early evening. Showers will follow for
late tonight into Thursday along with a slight chance of
thunderstorms.

For portions of the San Bernardino County, the snow level early
this morning may start out around 4000 feet before rising to 5500
to 6000 feet during the morning. For the Riverside County
mountains, the snow level will rise to around 6500 feet and above
6500 feet for the San Diego County mountains. The snow level will
then fall during the afternoon and night to around 4000 for late
tonight into Thursday morning.

Today and Thursday will be much cooler with high temperatures for
much of the coast and valleys on Thursday in the 50s. There will
periods of stronger and gusty southwest to west winds in the
mountains and deserts into Thursday with the stronger gusts to
around 60 mph. Dry with warming for Friday. High temperatures on
Friday will remain well below average, as much as 15 to 20 degrees
below average for portions of the mountains.

&&

.LONG TERM (Saturday through Saturday)...
The weekend will be warmer, but with high temperatures for the
weekend mostly a few degrees below average. For early next week,a
low pressure system will move inland through the western states
with cluster analysis showing timing and amplitude differences
among model ensemble members. It should be cooler with periods of
stronger and gusty southwest to west winds in the mountains and
deserts. While more significant precipitation is expected to
remain north of Point Conception, some light precipitation is
possible across portions of southwestern California some time on
Monday and Tuesday. NBM shows daily chances for measurable
precipitation mostly 20 percent or less.

&&

.AVIATION...
290830Z...Areas of BKN low clouds with bases 1500-2500 ft MSL
developing over San Diego County and spreading northwards into
portions of Orange County and the Inland Empire through the morning.
Otherwise increasing clouds in the 3000-7000 ft MSL layer as SCT
SHRA move in. These showers will spread over areas north of San
Diego County 09-14Z. The main band of precipitation will move east
across the area 14Z-22Z. Vis lowering to 2-4 SM with CIGS down to
1000 ft MSL in showers. Isolated IFR CIGS/VIS possible in heavier
showers with the main band. Desert TAFS (PSP/TRM) will only have
VCSH 17Z-02Z Thu with CIGs mostly remaining above 4000 ft MSL. Brief
drier period 30/00-06Z with only ISO light showers. Activity
increases and becomes more widespread again after 30/06Z. Coastal
mountain slopes will be obscured in clouds/fog at times through
Thursday.

Southwest to west winds will occur in the mountains and locally into
the deserts with gusts to 35-50 knots through tonight. MOD-STG
up/downdrafts likely over and NE/E of the mountains.

&&

.MARINE...
A storm will bring rain and gusty winds today and Thursday. West
winds around 20 kt with gusts 25 kt possible Thursday along with
combined seas to 9 ft and steep waves. Isolated thunderstorms are
also possible Wednesday night and Thursday, and these could produce
waterspouts.

&&

.BEACHES...
There is a slight chance of thunderstorms Wednesday night and
Thursday at the beaches with cloud-to-ground lightning possible.
Thunderstorms will most likely be isolated if they occur.

&&

.HYDROLOGY...
Widespread, mostly light precipitation will spread southward
across the area this morning, then decrease from the northwest
during the afternoon and early evening with the greatest amounts
along the coastal slopes of the mountains. Showers will follow
for late tonight into Thursday along with a slight chance of
thunderstorms. The snow level will rise to 6000 to 6500 feet this
morning, then fall to around 4000 feet for late tonight into
Thursday.

Through Thursday, rainfall and liquid equivalent in the mountains
above the snow level is expected to range from one-half to three-
quarters of an inch near the coast to 1.5 to 2.5 inches in the
mountains with locally greater amounts. One-quarter inch or less
is expected in the deserts. Snowfall of 6 to 10 inches is possible
in the mountains above 5000 feet with locally 12 to 18 inches on
higher peaks above 7500 feet. A few inches of snowfall is possible
at elevations down to around 4000 to 4500 feet.

Peak hourly rainfall rates of one-quarter to one-third per hour
are possible today, and briefly and locally to one-half to three-
quarters of an inch with isolated thunderstorms for late tonight
into Thursday.

With wet soil conditions, there will likely be more instances of
urban flooding and pooling of water in poorly drained areas.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 2 PM PDT Thursday for San Bernardino
     County Mountains.

     Winter Storm Warning from 10 AM this morning to 4 PM PDT
     Thursday for Riverside County Mountains.

     Wind Advisory from noon today to midnight PDT tonight for San
     Diego County Mountains.

     Winter Weather Advisory from midnight tonight to 4 PM PDT
     Thursday for San Diego County Mountains.

     Wind Advisory from noon today to 10 PM PDT this evening for
     Apple and Lucerne Valleys.

     Wind Advisory from noon today to 2 AM PDT Thursday for Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near
     Banning.

PZ...Small Craft Advisory from 3 AM to 5 PM PDT Thursday 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...17
AVIATION/MARINE/BEACHES...SS

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

3 heavy snow, 1 strong wind, 1 flood. Local standard time, as filed.

Heavy Snow, San Bernardino County Mountains

When: March 29, 4:00 AM PST to March 30, 2:00 PM PST
Where: San Bernardino County Mountains forecast zone
Reported by: Other Federal Agency
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Two rounds of precipitation impacted the San Bernardino County Mountains on March 29-30. The first round occurred during the day on March 29 had snow levels near 6000-7000 feet, before falling to 3500-4000 feet Wednesday night and Thursday with the second round of precipitation. The heaviest snow accumulations generally occurred above 6000 feet, where accumulations of 6-12 inches were observed. Lower elevations down to 4000 feet saw accumulations of 2-6 inches.

Heavy Snow, Riverside County Mountains

When: March 29, 10:00 AM PST to March 30, 4:00 PM PST
Where: Riverside County Mountains forecast zone
Reported by: COOP Observer
Coordinates: 33.744, -115.994 (the zone’s center; the record gives no point)

Snow fell across the Riverside County Mountains in two rounds: the first occurring through the day on Wednesday with snow levels near 6500 feet, and the second late Wednesday night through Thursday afternoon, when snow levels fell to 3500-4500 feet. Snow accumulations of 1 to 4 inches were reported in the mountains.

Strong Wind, San Diego County Valleys

When: March 29, 9:30 PM PST
Where: San Diego County Valleys forecast zone
Measured: 35 kt (40 mph) estimated gust
Reported by: Broadcast Media
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Broadcast media reports potential wind damage near three homes, with downed powerlines and a damaged, though non-secure, tent. A small shower with weak rotation moved over the area.

Heavy Snow, San Diego County Mountains

When: March 30, 12:00 AM PST to 4:00 PM PST
Where: San Diego County Mountains forecast zone
Reported by: COOP Observer
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Snow developed across the San Diego County Mountains late in the evening on March 29, persisting through the afternoon on March 30. The heaviest snow accumulations generally occurred above 5500 feet, where accumulations of 8-12 inches were observed. Lower elevations down to 4000 feet saw accumulations of 1-7 inches.

Flood, San Diego

When: March 30, 6:30 AM PST
Where: San Diego County, 1 mi WNW of Lemon Grove to 0.7 mi NW of Lemon Grove
Cause: Heavy Rain
Reported by: Department of Highways
Coordinates: 32.736, -117.036

The Department of Highways reported roadway flooding at SR-74W and College Grove Avenue, with 0.45-0.55 inch of rain reported in the previous 24 hours.

What these are

Heavy Snow: Snowfall reaching the local warning threshold without the other hazards of a winter storm.
Strong Wind: Non-thunderstorm winds below high wind criteria that nonetheless caused damage or casualties.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in California in 2023 Every state in 2023 This day in weather history Warnings in California, March 2023

Sources

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: 1086878, 1086889, 1086891, 1086885, 1087834.