A potent trough of low pressure associated with a weak atmospheric river brought heavy mountain and snow and areas of flooding rains across Southern California from January 28th to 29th.
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.
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 potent trough of low pressure associated with a weak atmospheric river brought heavy mountain and snow and areas of flooding rains across Southern California from January 28th to 29th.
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 Jan 27, 8:54 PM PST, 3 hours 6 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
854 PM PST Wed Jan 27 2021
.SYNOPSIS...
Mostly dry tonight with increasing clouds into Thursday. Late
Thursday into Friday, widespread precipitation is expected as a
low pressures system moves across Southern California. The weekend
into early next week will be mostly dry with some warming. Around
Tuesday, another low pressure system will move inland along the
West Coast and could bring some precipitation to the area.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.Evening Update...
Hello, evening readers. Taking a look at our latest storm system
on our doorstep, everything forecast-wise still looks on track
this evening. Diving into some of the higher resolution models,
the storm system may approach areas of the eastern LA metro a bit
earlier, most likely after 8 PM. After the system pushes through
SoCal, lighter showers will overspread much of the region. POPS
have been slightly adjusted a bit for timing differences. The
weekend looks fairly quiet, but we'll have to keep our eyes on
next week as we may see a cooler (and even wetter) pattern
develop by Tuesday.
.Previous Discussion (As of 146 PM Wednesday)...
The low pressure system that is expected to bring widespread rain
and mountain snow to SoCal Thursday evening into Friday, is
currently bringing widespread rain to northern and central
California. Lighter precipitation may make it to LA County early
Thursday but is unlikely to bring rain into Orange County or the
Inland Empire until Thursday evening. Temperatures tomorrow will
be a few degrees warmer than today but still 5 to 10 degrees below
average for this time of year. Much cooler conditions return on
Friday with temperatures 10 to 20 degrees below average.
Precipitation will become widespread and spread to the southwest
across California beginning Thursday evening. There is still some
uncertainty surrounding the onset of the heavy precipitation. HiRes
models are coming more into agreement that periods of heavy showers
could begin prior to 10 PM Thursday. Periods of heavy rain are
expected through into Friday morning, lingering into Friday
afternoon, or evening especially in San Diego County. An atmospheric
river will be feeding moisture into the system as it moves into our
area.
Rainfall is expected to range from around 1.25 inch to 1.70 inch in
the coast, valleys, and Inland Empire, 2 to 3 inches in the
mountains with 3 to 5 inches on south facing slopes of the San
Bernardino County mountains with locally greater amounts. High
desert areas are expected to receive around 0.50 inch to 0.75 inch,
with 0.25 inch to locally 0.50 inch in the lower deserts.
Runoff is expected to be greater due to heavier rainfall on soils
saturated by recent precipitation. With higher snow levels, snow
melt will add to the runoff, especially in the San Bernardino County
mountains. A Flash Flood Watch has been issued for all areas west of
the mountains below 5000 feet in elevation, including the burn
scars.
Snow levels will rise to 5500 to 6000 feet Thursday night, then fall
to around 4500 feet Friday afternoon. Snowfall of 4 to 10 inches is
expected above 5000 feet, 10 to 15 inches above 6000 feet, and 15 to
locally 30 inches above 7000 feet.
It's possible showers could linger into early Saturday morning, but
the rest of the weekend will be dry. Conditions will warm to near
average by Monday. The next chance for precipitation is around
Tuesday and Tuesday night as a trough of low pressure moves inland
along the West Coast.
&&
.AVIATION...
280420Z...SCT-BKN at/above 12000 ft MSL through Thu morning. Most
vis will remain above 6 miles through Thu. Clouds will increase Thu
afternoon with bases possibly lowering to 5000 ft MSL late. SCT-BKN
clouds could develop after 03Z Fri but impacts at TAF sites are
uncertain.
&&
.MARINE...
A storm system will move through coastal waters Thursday night with
increasing southerly winds, turning westerly Friday. Some gusts will
likely exceed 20 knots. A slight chance of thunderstorms Thursday
night into Friday could lead to hazardous marine conditions. No
marine weather hazards are expected Saturday through next Monday.
&&
.BEACHES...
Surf will build again Thursday ahead of the next storm. Sets to 7
feet are possible Thursday into Friday, mainly in southern San Diego
County but prevailing surf of 3-6 feet is expected. The bigger surf
will also bring a high rip current risk. There is also a slight
chance of thunderstorms Thursday night into Friday.
&&
.HYDROLOGY...
There is still some uncertainty surrounding the onset of the heavy
precipitation but it looks like it will begin late in the day
Thursday into Thursday night in Orange and San Bernardino Counties.
Precipitation will spread across southwestern California becoming
heavy at times into Friday morning. Showers will continue Friday
afternoon and end from the northwest Friday night. The ECMWF still
has ensemble members trending slightly slower in timing, extending
the duration of potentially heavy rain into Friday evening,
especially in San Diego County. There is a slight chance for
thunderstorms for Thursday night and Friday.
Rainfall is expected to range from around 1.25 inch to 1.70 inch in
the coast, valleys, and Inland Empire, 2 to 3 inches in the
mountains with 3 to 5 inches on south facing slopes of the San
Bernardino County mountains with locally greater amounts. High
desert areas are expected to receive around 0.50 inch to 0.75 inch,
with 0.25 inch to locally 0.50 inch in the lower deserts.
Runoff is expected to be greater due to heavier rainfall on soils
saturated by recent precipitation. With higher snow levels, snow
melt will add to the runoff, especially in the San Bernardino County
mountains. A Flash Flood Watch has been issued for all areas west of
the mountains below 5000 feet in elevation, including the Apple/El
Dorado, Bond, Blue Ridge, Silverado, and Valley burn scars.
Snow levels will rise to 5500 to 6000 feet Thursday night, then fall
to around 4500 feet Friday afternoon. Snowfall of 4 to 10 inches is
expected above 5000 feet, 10 to 15 inches above 6000 feet, and 15 to
locally 30 inches above 7000 feet.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flash Flood Watch from Thursday evening through Friday afternoon
for 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
Mountains-San Diego County Valleys-Santa Ana Mountains and
Foothills.
Winter Storm Warning from 3 PM Thursday to 3 PM PST Friday for
San Bernardino County Mountains.
Winter Storm Warning from 6 PM Thursday to 3 PM PST Friday for
Riverside County Mountains.
PZ...NONE.
&&
EVENING UPDATE...APR
PUBLIC/HYDROLOGY...CO
AVIATION/MARINE/BEACHES...PGThe Edwards AFB radar (KEYX), 129 km away, was scanning. The volume nearest the first event began at 08:02 UTC.
5 flood, 4 heavy rain, 3 heavy snow, 1 high wind, 1 debris flow, 1 flash flood. Local standard time, as filed.
The storm produced close to one foot of snowfall as measured by trained spotters, as well as high-elevation ski resorts reporting over 2 feet.
CalTrans reports various spots of near one foot of storm total snowfall.
Widespread snowfall occurred, including 13 inches on Palomar Mountain.
Spotter reports 1.34 inches of rain.
Spotter reports 1.6 inches of heavy rainfall.
Observer reports 1.1 inches of rainfall.
Observer reports 1.21 inches of rainfall.
Gusty winds occurred at the desert slopes of the region over 60 MPH. Burns Canyon reported a peak gust of 77 MPH.
I-805 flooding in far right lane just north of main street.
Reports of large amounts of mud and debris covering roadways and damaging homes in Silverado Canyon area. The area saw around 1.5 inches of rainfall from this system.
Vehicle stuck in water on San Jacinto and Murrieta Rd in Perris., where a water rescue was conducted.
Escondido Creek flowing causing, Country Club Drive to close near Harmony Grove Road.
Via Vera Cruz closed between Discovery Street and W. San Marcos Blvd through riverbed.
Large pool of water in lane 1 with vehicles hydroplaning. 0.25 to 0.30 inches past 2 hours and thunderstorms passage. Occurred on the north connector of 125 to highway 94.
San Diego fire department and rescue and U.S. Border Patrol report 8 people trapped in a flooding storm drain between Otay Mesa and San Ysidro. 7 people were helped to safety with one fatality.
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 |
|---|---|---|---|---|---|
| Flash Flood, San Diego | 2021-01-29 | Other | Direct |
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, January 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: 938850, 938852, 938854, 938883, 938884, 938887, 938888, 938881, 938894, 938897, 938886, 938891, 938889, 938893, 938895.