A Pacific trough brought areas of heavy rainfall and mountain snow across the region on March 3rd and 4th, as well as small hail. An area of thunderstorms produced heavy rain in the San Diego metro.
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.
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 Pacific trough brought areas of heavy rainfall and mountain snow across the region on March 3rd and 4th, as well as small hail. An area of thunderstorms produced heavy rain in the San Diego metro. 22 cloud to ground lightning strikes detected.
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 2, 9:23 PM PST, 2 hours 37 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
923 PM PST Tue Mar 2 2021
.SYNOPSIS...
It will be clear and not quite as cool tonight as humidity gradually
recovers ahead of a Pacific storm slated to arrive on Wednesday.
Fair skies early Wednesday morning will cloud over as a storm system
off the coast approaches and moves inland with periods of showers
and thunderstorms. The showers will taper off overnight and end
Thursday morning, setting us up for fair and warmer weather through
Friday. A trough passing to the north on Saturday, will bring gusty
winds and cooler weather.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Skies were clear again this evening over SoCal and winds were mostly
light. The sfc pressure gradients were trending slowly back onshore
as sfc dewpoints rise. The 00Z Miramar sounding still showed we had
a way to go as far as moisture is concerned. The PW was only 0.16
inch, but southerly winds have really ramped up throughout the
column. This flow will gradually increase the atmospheric moisture
ahead of the incoming storm for tomorrow.
Latest model guidance continues to support the timing and intensity
of this system as it arrives and moves inland. A few lightning
strikes have already been detected near the storm center, which was
550 miles due west of San Diego at 7 PM PST. Scattered showers could
break out mid morning over coastal areas, then become more numerous
through midday as they spread inland. Total storm rainfall based on
latest short-term model guidance is for one-quarter to three-
quarters inch for the coast and valleys, and 0.5-1.5 inches in the
mountains. Some of this could make it over the mountains into the
deserts as well, but amounts look to be light. The one exception is
San Diego County where the heavier totals are forecast. The County
deserts may surprise on the upside due to the deep saturation and a
brief subtropical moisture tap. A few thunderstorms are expected,
and the latest NBM guidance pegs KSAN at a 22% chance.
In terms of snow...Evaporative cooling may drive down snow levels
initially, but they are expected to stabilize around 5K-5.5K FT
through the afternoon under strong S-SW flow aloft. A Winter Weather
Advisory will be in effect from 1 PM to 10 PM Wednesday above 5,000
feet in the northern mountains, and above 5,500 feet in the San
Diego County mountains. Snow amounts are forecast to be a Trace to
1" at 5,000 feet, 1-3" from 5,000-7,500 ft, and from 3-6" above
7,500 feet. Strong SW winds with gusts to 60 MPH will accompany the
rain and snow over the San Diego county mts. The precipitation ends
Thursday morning in the mountains, followed by weak ridging that
will bring dry, cool weather Thursday, and slightly warmer weather
Friday.
For the coming weekend, a weak trough will move inland across
northern California. It will produce gusty westerly winds over the
mountains and deserts, and cooling, but most of the precipitation
with it looks to stay north of SoCal. Another passing, weak ridge
will bring dry weather and seasonal temperatures on Sunday.
The global models show a persistent longwave trough near the West
Coast next week, a parade of disturbances will be moving through the
mean trough position, posing forecast challenges for SoCal as
evidenced by the split QPF ensemble solutions. At least it looks
like March will not come up dry for much of the State, and the
cooler weather will support more snowpack in the Sierra. This will
likely not wipe out our precip deficit this season, but it is
promising for the State's water supply this year.
&&
.AVIATION...
030515Z...Coast/Valleys...Mostly clear skies will prevail tonight
with mostly unrestricted vis. Clouds will increase Wed after 13Z
with bases 1500-2500 ft MSL with some higher terrain obscured, but
vis mostly above 5 miles below the bases. SHRA with a slight chance
of TSRA will develop 18Z-20Z Wed and continue at times into Wed
evening. Areas of gusty south winds will occur Wed especially along
the coast where surface speeds will be 15-25 knots with gusts to 30
knots.
Mountains/Deserts...Mostly clear skies will prevail tonight with
unrestricted vis. Clouds will increase Wed after 15Z with bases 3500-
6000 ft MSL, except to 8000 ft MSL in the deserts, with higher
terrain obscured. SHRA with SHSN above 5000-5500 feet MSL will
develop 20Z-22Z Wed and continue into Wed evening. Gusty southwest
winds 20-35 knots with gusts to 45 knots will occur on the mountain
crests and desert mountains slopes, especially San Diego County, 16Z
Wed-02Z Thu, along with locally strong up/downdrafts.
&&
.MARINE...
Gusty south to southwest winds 15 to 20 knots with gusts 25 to 30
knots will occur Wednesday morning, shifting southwest during the
early afternoon. Isolated thunderstorms are possible Wednesday
afternoon and evening. No hazardous marine weather is expected
Thursday and Friday. Breezy northwest winds will be possible
Saturday afternoon across the outer coastal waters.
&&
.BEACHES...
Isolated thunderstorms will be possible late Wednesday morning into
early Wednesday evening. Storms will be capable of producing cloud-
to-ground lightning and gusty and erratic winds.
&&
.HYDROLOGY...
The soil is dry after weeks of little to no precipitation and
periods of dry Santa Ana winds, so it will have the capacity to
absorb a good portion of the rainfall we expect. If it fell at a
gentle to moderate pace, flooding would not be a major concern, but
there are indications of possible thunderstorms and locally heavy
rainfall rates with some of these cells. So, depending on how these
develop and track, localized flooding will be possible, especially
in and below burn scars and poorly drained urban areas Wednesday
afternoon and evening.
Mainstem river flooding is not expected, although there is about a
10% chance that the San Diego River could reach Monitor Stage
Wednesday evening, which could briefly impact the low-water
crossings in Mission Valley. Another potential problem area is the
flood plain along the Tijuana River. These are low probability
&&
.SKYWARN...
Skywarn activation may be needed on Wednesday.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 1 PM to 10 PM PST Wednesday for
Riverside County Mountains-San Bernardino County Mountains.
PZ...Small Craft Advisory from 6 AM to 6 PM PST Wednesday 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...10
AVIATION/MARINE/BEACHES...MaxwellThe San Diego radar (KNKX), 41 km away, was scanning. The volume nearest the first event began at 07:55 UTC.
3 flood, 1 heavy rain, 1 high wind, 1 hail. Local standard time, as filed.
The valleys and mountains of San Diego County saw appreciable rainfall with some places reaching near 1.5 inches of rain in total.
Gusty winds occurred across the mountains in excess of 70 MPH in some areas.
Law enforcement reports considerable standing water at State Route 52 and Interstate 15. Heavy rain and thunderstorms moving through area at the time.
Law enforcement reports standing water on all lanes of Interstate 805 at Murray Ridge Road interchange by CHP. Thunderstorm were moving across this area with at least 0.50 per hour rain rates.
Several reports of hail ranging from 1/4 to 1/2 inch size with photos on social media in the San Diego metro area.
CHP reports lanes of Highway 91 at Highway 241 flooded. Lanes 1 and 2 flooded and water moving into HOV lanes. Rainfall rates were around one quarter of an inch per hour in some spots.
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: 945196, 945226, 945206, 945211, 952429, 945222.