A West Coast trough of low pressure impacted Southern California March 9th through 13th. This storm brought periods of windy conditions across the mountains and deserts, along with widespread rain and snowfall, and areas of flooding and debris flows being observed as well.
Every event with a place to put it; 8 filed by county or forecast zone are drawn at its center, in a lighter ring. 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 West Coast trough of low pressure impacted Southern California March 9th through 13th. This storm brought periods of windy conditions across the mountains and deserts, along with widespread rain and snowfall, and areas of flooding and debris flows being observed as well.
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 8, 9:22 PM PST, 2 hours 38 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
922 PM PST Mon Mar 8 2021
.SYNOPSIS...
Tuesday will be cooler across the board, with gusty winds across
the mountains and deserts preceding the approaching storm system.
This system will bring widespread rain, heavy low-elevation snow,
and a few thunderstorms to the region Wednesday and Thursday. The
Winter Storm Watch was upgraded to a Winter Storm Warning this
evening. The cold will be very noticeable mid week, with highs
locally 20 degrees below normal Wednesday and Thursday. Some
showers may continue into Friday, especially in the mountains and
High Desert, before the storm exits the region and ushers in
warmer and drier weather for the weekend.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Highlights...
* Winter Storm Warning for mountains starting Tuesday night
* Heavy, low elevation snow to impact some major passes
* Widespread rain and isolated thunderstorms Wed-Thu
* Much colder than normal mid week
* Showers may continue into Friday. Drier for the weekend.
We may have recently entered meteorological spring, but
winter is about to come knocking back at our door. The low
pressure trough centered off the PacNW coast will continue to
deepen into Tuesday, ushering in noticeably cooler temperatures,
particularly for the mountains and deserts. As onshore pressure
gradients tighten, winds will respond accordingly, with gusty west
winds surfacing across the desert-facing mountain slopes and
passes. These will persist into Wednesday, and locally longer,
especially for the San Gorgonio Pass area.
It is not until Tuesday night that the first few pre-frontal
showers will make an appearance, but the more widespread
precipitation is still slated for Wednesday and Thursday. A mostly
weak cold front Wednesday will bring largely moderate rain and the
first round of heavy snow to the mountains. 700 mb temperatures
lowering to around -10 C Wednesday will bring down snow levels
to around 4,000 ft, locally lower in San Bernardino County.
Instability will increase in the afternoon, with ample cold air
aloft and favorable jet positioning leading to scattered post-
frontal showers and likely a few thunderstorms west of the
mountains. Temperatures will continue to fall, with highs a good
10 to 20 degrees below normal Wednesday, and locally even 25
degrees below average.
The cold will only reaffirm its grip over the region Wednesday
night and Thursday, as the approaching low pressure center
continues forcing snow levels to fall. Snow can be expected above
3,000 to 3,500 feet for northern portions of our forecast area
Thursday, and around 500 ft higher in San Diego County. There is
high confidence in significant travel impacts to Cajon Pass and
potentially I-8 through Laguna Summit. Highs both days will
struggle to hit the mid to high 50's across most of our coastal
and valley areas. With the jet streak remaining due south
Thursday as the trough digs over SoCal, we'll remain under a
dynamically favorable environment for thunderstorms, with
precipitation largely of showery characteristics.
Although the bulk of the precipitation will fall through Thursday
night, we're not entirely out of the woods for Friday either. As
the low tracks inland and northerly flow rotates along its western
periphery, there's decent potential for additional wrap-around
moisture and showers, mainly for the mountains and High Desert.
Both ensemble guidance and local WRF products hint at this
potential, and a glance at the ECMWF Shift of Tails suggests we
cannot rule out significant additional snowfall impacts for these
areas if this scenario plays out.
Weak ridging will fill in for the weekend, bringing us an increase
in temperatures and drier weather. The pattern beyond the weekend
looks like a "time will tell" situation, with a wide realm of
possibilities. For now, the focus remains on the upcoming
significant winter storm. For more information on snow totals and
snow levels, see the Winter Storm Warning, and for more
information on rainfall totals and rates, see the Hydrology
section below.
&&
.AVIATION...
090415Z...Coast/Valleys...Mostly VFR conditions through 22Z Tuesday
with SCT020 BKN200 and only ocnl BKN020 at times. West winds
increasing after 18Z Tuesday to 15-25 kt at the coastal and valley
airports with gusts to 30 kt.
Mountains/Deserts...Gusty west winds 20-30 kt with gusts to 45 kt in
the mountains and some desert areas through Tuesday with LLWS and
moderate up/downdrafts.
&&
.MARINE...
A Small Craft Advisory is in effect through 9 PM Tuesday. Northwest
winds 15-25 kt over the Outer Waters will move into the Inner Waters
after midnight and continue through Tuesday afternoon.
Gusty west winds at times Tuesday night, Wednesday and Thursday as a
cold winter storm moves across Southern California. Rain is likely
Wednesday with scattered showers Thursday. Thunderstorms with strong
winds, rough seas and lightning are also possible.
&&
.BEACHES...
Elevated surf from 3 to 6 feet Tuesday. Gusty west winds 15 to 30
mph at the beaches in the afternoon. Above average surf from 3 to 6
feet continues Wednesday and Thursday with showers and possible
thunderstorms.
&&
.HYDROLOGY...
A slow moving storm system will bring periods of rain and mountain
snow beginning early Wednesday, and possibly continuing through
Friday, with the heaviest precipitation expected Wednesday into
Thursday. The main frontal band will move through on Wednesday,
with mostly moderate rain. This will be followed by widespread
scattered showers and likely a few thunderstorms through Thursday.
Thus, storm totals will be spread out over several days, with the
main impact being snowfall. Since the storm will be quite cold,
snow levels may be as low as 2500 FT at times with convective
showers. Moisture will be limited with this event, so rainfall
totals are not excessive for a Winter Storm. Current estimates
range from 0.50 to locally 1.25 inches for the coast and valleys,
and 1.5 to locally 2.5 inches (liquid equivalent) in the
mountains (mostly as snow). The deserts will be drier, and are
expected to mostly pick up 0.25" or less, with locally higher
amounts up to around 0.30" for the High Desert.
Rainfall rates will be light to moderate overall (0.10 to 0.30/hr.),
with some briefly heavier rainfall rates possible during heavier
showers and thunderstorms. Some runoff is likely, with the
greatest impact in urban and poorly drained areas, but widespread
flooding and mainstem river flooding is not likely. Snow levels
near 4500 feet will lower to around 4000 feet Wednesday afternoon
and 3500 feet or less for Wednesday night and Thursday. This will
further limit any significant runoff, and eliminate the risk of
debris flows for the El Dorado and Apple burn scars.
Showers should taper off on Friday, but there's potential for
wrap-around moisture to enhance snowfall totals in the mountains
and generate additional showers for the High Desert before the
system completely exits the region Friday night.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning from 10 PM Tuesday to 10 PM PST Thursday
for Riverside County Mountains-San Bernardino County
Mountains-San Diego County Mountains.
Wind Advisory until 4 AM PST Friday for San Gorgonio Pass Near
Banning.
PZ...Small Craft Advisory until 9 PM PST Tuesday for Waters from
San Mateo point to the Mexican Border and out to 60 nm.
&&
SYNOPSIS/PUBLIC DISCUSSION/HYDROLOGY...Rodriguez
AVIATION/MARINE/BEACHES...MoedeThe San Diego radar (KNKX), 28 km away, was scanning. The volume nearest the first event began at 07:59 UTC.
5 heavy snow, 3 high wind, 1 heavy rain, 1 debris flow, 1 flash flood, 1 hail. Local standard time, as filed.
Gusty winds occurred across the region, mostly 45-60 MPH with localized pockets of higher gusts.
Gusty winds occurred across the region, mostly 45-60 MPH.
Gusty winds occurred across the region, mostly 45-60 MPH.
Multiple members of the public and ski resorts report storm total snow one to two feet across the region.
Reports of 6-12 inches of storm total snow occurred across the region.
Reports of 6-18 inches of storm total snow occurred across the region. 6 inches of snow in 3 hours on Palomar Mountain due to thundersnow. Both locations at 5000 to 5700 feet reported total snowfall of 18 to 24 inches.
Portions of the eastern Inland Empire received a couple inches of snow, such as Cherry Valley with two inches at an elevation of 5,000 feet.
Areas of the San Diego county mountains received heavy rainfall out of this storm system, with some areas over 2 inches in total. Pine Hills reported 2.82 inches of rain.
Heavy rain of near 0.20 inches in 15 minutes occurred between 6 and 7 am over Bond fire scar near the Silverado Canyon and this prompted evacuation orders of residents. The debris flow brought areas of mud and debris over roads and into homes. This caused damage to 6 homes and 8 vehicles in the town of Silverado. This also closed Silverado Canyon Road between Olive Drive and Ladd Canyon Drive.
Confirmed 8 vehicles were damaged by a mud and debris flow on the Bond Fire. 6 homes had mud and water damaged. Swift water rescues were performed around 6 to 7 am at the peak of the mud and debris flows. Mud covered at least 3 locations on Silverado Canyon road and at Silverado Cafe. Rainfall rates as high as 0.20 inches in 15 minutes between 6 and 7 am.
Palomar Mountain reported a total of 23 inches. 6 inches occurred in 3 hours during a thunderstorm. Julian at 5000 feet report 18 inches of snow while Palomar mountain was reporting the same amount. Water equivalent was 2.5 to 3 inches.
Thunderstorms late afternoon on March 11 produced 1/4 to 1/2 inch hail.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, March 2021
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: 948442, 948444, 948445, 948446, 948447, 948448, 948449, 948560, 948561, 952447, 952449, 952448.