Flash Flooding and Debris Flows in California, March 10 to 13, 2020

Name: Flash Flooding and Debris Flows in California, March 10 to 13, 2020
Start: 2020-03-10T17:00
End: 2020-03-13T08:00
Location: California

March 10 to 13, 2020 · NWS SGX · 13 events in 4 counties and zones

Where it happened

Every event with a place to put it; 1 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: 1
Injuries: 0
Property damage: $5,000
Crop damage: None recorded
Events: 13

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.

An atmospheric river moved into the California bight on March 10th, bringing heavy rainfall and mountain snow to Southern California. A closed upper low moved into the region on March 12, bringing a southerly moisture surge, resulting in more heavy rain (especially in the deserts) and mountain snow. Rainfall totals in the deserts were 1 to 2 inches on March 12th and 550 lightning strikes occurred. Flash flooding occurred in the deserts near Canebrake and Borrego Springs. Snowfall occurred above 7000 feet on March 10th and above 6000 feet on March 12th.

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 10, 12:48 PM PST, 4 hours 12 minutes earlier.

Area forecast discussion, Mar 10, 12:48 PM PST, 4 hours 12 minutes before

Area Forecast Discussion
National Weather Service San Diego CA
148 PM PDT Tue Mar 10 2020

.SYNOPSIS...
A slow moving low pressure system will continue precipitation at
times into Wednesday morning, along with a slight chance of
thunderstorms this afternoon and evening. Mostly dry weather will
develop late Wednesday and Wednesday night, then another round of
significant precipitation arrives Thursday into early Friday.
Smaller chances for light showers will continue through the
weekend. A low pressure system from the north will bring greater
chances for more significant precipitation early next week with
lower snow levels.

&&

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

At 1 PM, water vapor satellite showed an upper-level low around
400 miles west of San Diego, with enhanced atmospheric moisture
over and south of southern California. Scattered showers and
isolated thunderstorms were moving north to northeast across the
area, with isolated heavy precipitation. Snow levels remain high,
between 8000-9000 ft. The precipitation summary was updated at 1
PM for 24-hour totals, and also includes snowfall reports. Urban
and small stream flooding is possible in showers, with isolated
flash flooding possible in heavier showers/thunderstorms that
train over the same area.

The low will slowly move towards Point Conception through early
Wednesday, then move south and eventually east across northern
Baja Thursday night. This should give us a break in precipitation
Wednesday late afternoon through Wednesday night, then wrap-
around moisture and the traversing upper-low will create the
possibility of another round of heavy showers across the region
Thursday afternoon through Thursday night with snow levels mainly
above 7000 ft. Cold air aloft will yet again provide the
possibility of isolated thunderstorms, mainly late Thursday. A
Flash Flood Watch may be needed for the time period. Please see
the Hydrology section below for precipitation amounts and details.

The low will move quickly eastward across Arizona on Friday and
weaken while another low pressure system off the Pacific Northwest
coast moves slowly southward near the West Coast for the weekend
into early next week. Weak onshore flow and weak cyclonic flow
aloft from the next low pressure system from the north will
maintain a slight chance of light showers along and west of the
mountains for Friday night into Saturday morning. Saturday
afternoon and evening should be mostly dry, then a slight chance
of mostly light showers will return from the coast to the
mountains for late Saturday night into Sunday morning.

For Sunday into early next week, there is some spread in the
timing and placement of the low pressure system as it moves
southward near the West Coast. There is a chance for a return of
more significant precipitation Monday or Tuesday, but confidence
is low at this time. While snow levels will be fairly high for
much of the precipitation this week, snow levels will begin to
lower this weekend and be significantly lower for early next week
down to 3000-4000 ft.

&&

.AVIATION...
102000Z...BKN-OVC clouds bases 3000-5000 feet MSL with occasionally
merging layers above to near 11000 feet MSL, and mountains
frequently obscured. Visibilities generally 3-5 miles, except CIGS
1000-2000 feet MSL and visibilities 1-3 miles in occasional showers.
Slight chance of thunderstorms, mainly this afternoon and tonight.
The risk of thunderstorms and confidence in coverage and timing are
too low to mention in the TAFS. Areas of southeast winds 15-30 knots
at times with highest winds mostly in the mountains. Local moderate
to strong up and downdrafts along with wind shear. Precipitation
will become more scattered late tonight and Wednesday.

&&

.MARINE...
Wind gusts to near 20 knots at times will continue to decrease.
There remains a slight chance of thunderstorms, mainly late
afternoon through tonight, which could generate cloud-to-water
lightning, strong gusty winds, choppy seas and brief heavy rain. A
Marine Weather Statement has been issued to cover this hazard.

&&

.BEACHES...
There is a slight chance of thunderstorms mainly late afternoon and
tonight with cloud-to-ground lightning possible. Surf will increase
to 3 to 5 feet with sets to 6 feet mainly over the Orange and
northern San Diego County beaches by tonight and Wednesday.

&&

.HYDROLOGY...
Through tonight, additional rainfall is expect to range from
around 0.25 to 0.50 inch near the coast to 0.75 to 1.50 inches in
the mountains with locally greater amounts. Rainfall of 0.25 to
0.50 inch is expected in the lower deserts and 0.10 to 0.25 inch
in high desert areas. Peak rainfall rates into this evening in
heavier showers and isolated thunderstorms will be mostly one half
inch or less per hour with localized flooding of poor drainage
areas.

For Wednesday morning and afternoon, additional rainfall is
expected to be around 0.10 inch or less to 0.25 in the mountains.

For Thursday into Friday, additional rainfall is expected to
range from 0.50 to 1.00 inch at lower elevations to 1.50 to 2.50
inches in the mountains with locally greater amounts.

Snow levels will be mostly 7000 feet and above, with snowfall
mostly limited to the highest peaks.

&&

.SKYWARN...
Skywarn activation is requested for all areas today.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Wednesday morning for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

PUBLIC/HYDROLOGY...JJT
AVIATION/MARINE/BEACHES...Small

In the hours before

Local storm report, Mar 10, 1:15 PM PST, 3 hours 45 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
215 PM PDT TUE MAR 10 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0140 PM     HEAVY RAIN       5 NW VALLEY CENTER      33.27N 117.11W
03/10/2020  E0.95 INCH       SAN DIEGO          CA   DEPT OF HIGHWAYS

            MUD AND WATER ACROSS ROAD. AREA HAS SEEN
            AROUND AN INCH OF RAIN.

&&

CO

Local storm report, Mar 10, 4:27 PM PST, 33 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
527 PM PDT TUE MAR 10 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0446 PM     FLOOD            3 SW CHINO HILLS        33.96N 117.78W
03/10/2020                   SAN BERNARDINO     CA   PUBLIC

            STREET FLOODING NEAR CHINO HILLS.

&&

MGM

The radar

The San Diego radar (KNKX), 11 km away, was scanning. The volume nearest the first event began at 00:59 UTC.

Open the radar archive at this moment

Event by event

5 flash flood, 4 flood, 2 debris flow, 1 heavy snow, 1 lightning. Local standard time, as filed.

Flood, San Diego

When: March 10, 5:00 PM PST to 7:00 PM PST
Where: San Diego County, 0.84 mi W of (See)san Diego Gille to 0.78 mi W of (See)san Diego Gille
Cause: Heavy Rain
Deaths: 0 direct, 1 indirect
Reported by: Broadcast Media
Coordinates: 32.830, -116.984

Between 6pm and 8pm on March 10th, heavy rain in El Cajon and Santee was observed. A vehicle was traveling on I-8 westbound when it crashed into the Forrester Creek canal near First street and Naranca Avenue in El Cajon. As they were trying to escape, one of the passengers got caught in the fast-moving canal (but still within its banks) and was swept miles away. The person was located about 5 miles down Forrester creek near Prospect Avenue in Santee. When pulled from the water, the individual was alive but unconscious, but was later pronounced dead at the hospital.

Debris Flow, Riverside

When: March 12, 12:00 PM PST to 2:00 PM PST
Where: Riverside County, 9.74 mi SW of La Quinta to 9.75 mi SW of La Quinta
Cause: Heavy Rain
Reported by: Lifeguard
Coordinates: 33.586, -116.436

Report of a mudslide near mile marker 74 on Highway 74 near Pinyon Pines.

Heavy Snow, San Bernardino County Mountains

When: March 12, 12:00 PM PST to March 13, 8:00 AM PST
Where: San Bernardino County Mountains forecast zone
Reported by: Trained Spotter
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Between 7 and 12 inches of snow fell in the San Bernardino Mountains from Thursday afternoon (March 12) through Friday morning (March 13).

Flood, Riverside

When: March 12, 1:00 PM PST to 3:00 PM PST
Where: Riverside County, 2.52 mi NNE of Coachella to 2.51 mi NNE of Coachella
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 33.715, -116.170

California Highway Patrol reports flooding along I-10 west near Coachella.

Flash Flood, Riverside

When: March 12, 1:00 PM PST to 3:00 PM PST
Where: Riverside County, 1.81 mi ENE of Arlington to 1.82 mi ENE of Arlington
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 33.928, -117.420

California Highway Patrol reports Highway 91 at the Adams Street off ramp completely flooded, with vehicles floating.

Debris Flow, Riverside

When: March 12, 1:00 PM PST to 3:00 PM PST
Where: Riverside County, 3.81 mi ENE of Indio to 3.88 mi ENE of Indio
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 33.742, -116.165

California Highway Patrol reports mud in the road on Dillion Road with cars stuck.

Flash Flood, San Bernardino

When: March 12, 1:00 PM PST to 3:00 PM PST
Where: San Bernardino County, 0.9 mi SE of Champagne to 0.92 mi SE of Champagne
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 34.019, -117.541

HOV lanes on Highway 60, just east of I-15, flooded with approximately 2 ft of water.

Lightning, Riverside

When: March 12, 2:00 PM PST to 3:00 PM PST
Where: Riverside County, 1.12 mi NE of Palm Desert
Property damage: $5,000
Reported by: Fire Department/Rescue
Coordinates: 33.730, -116.365

Riverside County Fire responded to a palm tree on fire next to a home. The tree was struck by lightning.

Flash Flood, San Bernardino

When: March 12, 2:00 PM PST to 3:00 PM PST
Where: San Bernardino County, 1.19 mi E of Crown Jewell to 1.2 mi E of Crown Jewell
Cause: Heavy Rain
Reported by: Public
Coordinates: 34.070, -117.199

Road damage at Lugonia and Tennessee ave with severe erosion.

Flood, Riverside

When: March 12, 2:00 PM PST to 4:00 PM PST
Where: Riverside County, 1.29 mi ESE of Corona Muni Arpt to 1.36 mi ESE of Corona Muni Arpt
Cause: Heavy Rain
Reported by: Broadcast Media
Coordinates: 33.894, -117.579

Rescue of 2 adults and a minor from a heavily flooded storm channel near Lincoln Avenue and Rincon Street in Corona. Unknown how they entered channel or if it was overflowing.

Flash Flood, Riverside

When: March 12, 2:00 PM PST to 5:00 PM PST
Where: Riverside County, 0.61 mi N of Lakeview to 0.62 mi N of Lakeview
Cause: Heavy Rain
Reported by: Public
Coordinates: 33.839, -117.119

Roadway completely submerged under approximately 2 feet of water at Hansen Ave and Ramona Expressway.

Flash Flood, Riverside

When: March 12, 3:00 PM PST to 5:00 PM PST
Where: Riverside County, 1.42 mi S of Glen Avon
Cause: Heavy Rain
Reported by: Fire Department/Rescue
Coordinates: 34.000, -117.476

Water rescue performed on two individuals stuck in their vehicle. 3 to 4 ft of water reported around the vehicle, at the intersection of Pedley rd and Jurupa rd.

Flood, San Bernardino

When: March 12, 5:00 PM PST to 6:00 PM PST
Where: San Bernardino County, 1.37 mi ENE of Apple Vly to 1.38 mi ENE of Apple Vly
Cause: Heavy Rain
Reported by: Public
Coordinates: 34.526, -117.177

Between one half and one foot of standing water across the intersection of Tonikan rd and Cholena rd in Apple Valley.

The people who died

As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.

Event	Date	Age	Sex	Where	Kind
Flood, San Diego	2020-03-10	68	Female	In Water	Indirect

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
Debris Flow: A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.
Heavy Snow: Snowfall reaching the local warning threshold without the other hazards of a winter storm.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Lightning: A lightning strike that killed, injured or caused damage.

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

The same day elsewhere

Every storm in California in 2020 Every state in 2020 This day in weather history Warnings in California, March 2020

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: 883022, 883073, 883098, 883074, 883089, 883090, 883091, 883092, 883093, 883094, 883095, 883096, 883097.