An atmospheric river impacted Southern California right before Christmas 2021 with heavy rain, high elevation snow, and windy conditions. Some areas reported over 5 inches of rainfall.
Every event with a place to put it; 5 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.
An atmospheric river impacted Southern California right before Christmas 2021 with heavy rain, high elevation snow, and windy conditions. Some areas reported over 5 inches of rainfall. This led to flooding, debris flows and closed roads.
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 Dec 23, 5:02 AM PST, 4 hours 58 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
502 AM PST Thu Dec 23 2021
.SYNOPSIS...
Light rain will become heavy at times tonight into early Friday
with widespread heavy rainfall fed by an atmospheric river.
Showers will then gradually decrease through the afternoon. A
moist northwest flow pattern will continue through the middle of
next week with additional periods of precipitation likely, but
with low confidence in timing and amounts. The next round of more
widespread precipitation may arrive for Saturday night into
Sunday with snow levels lower and precipitation amounts
significantly less.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM (Today through Saturday)...
An atmospheric river, at the upper end of moderate strength, will
continue the spread of moisture into the area through tonight with
the GFS and ECMWF ensemble systems a few hours different with the
peak with the GFS ensemble system a little faster and the ECMWF
ensembles a little slower. The current incoming 12Z NKX sounding
shows a completely saturated layer from 850 mb to 650 mb.
Light rain has spread into the area overnight with the most
widespread rain from Los Angeles County westward. Lighter
rainfall will continue into this afternoon. More widespread
rainfall fed by an atmospheric river will spread southward across
the area during the late afternoon and early evening with rainfall
becoming heavy at times for late tonight into Friday morning with
hourly rainfall up to 0.60 inch. The ECMWF Extreme Forecast Index
still has a sizable area of rainfall between the 80th and 90th
percentiles across portions of the area.
One area that needs to be evaluated further is the potential for
thunder for late tonight into Friday. Overnight, there have been
some lightning strikes in that moisture band with the atmospheric
river well to the southwest of the area, mostly south of 20N
latitude. The ECMWF Extreme Forecast for CAPE has values in the
80th to 90th percentile extending into the area, mainly toward the
coast. Higher NBM 3-hour thunder probabilities move south and
eastward late tonight into Friday morning from coastal Los Angeles
County into coastal areas of Orange and San Diego Counties into
the adjacent valleys with 12-hour thunder probabilities from 4 AM
to 4 PM Friday of 15 to 20 percent in that area centered along the
coast.
Gusty south to southeast winds will become southwesterly late
tonight into Friday with the strongest gusts on the desert slopes
of the mountains with stronger gusts to around 60 mph.
Snow levels above 8000 feet will fall during the day on Friday to
around 6500 feet late in the day. Snow is most likely on the
highest peaks, above 8500 feet, with lighter snowfall possible
down to around 7500 feet.
A moist northwest flow pattern will follow with periods of mostly
lighter showers continuing through Christmas day.
&&
.LONG TERM (Sunday through Wednesday)...
A moist northwest flow pattern will remain across the area into
the middle of next week with additional periods of precipitation
likely, but with low confidence in the timing and amounts. The
next round of more widespread precipitation may arrive for
Saturday night into Sunday with snow levels lower and
precipitation amounts significantly less.
In the ECMWF ensembles for Monday through Thursday there is quite
a spread in potential amounts from little or none to heavy. That
can also been seen in the NBM probabilistic precipitation amounts
with lower chances for measurable precipitation than with the
incoming storm, but with still a few percent chance of amounts at
higher thresholds above one inch.
&&
.AVIATION...
231130Z...ALL AREAS...BKN-OVC clouds above 6,000 ft MSL through this
morning, then lowering to 3,000 to 4,000 ft MSL after 21Z this
afternoon. Coastal mountain slopes becoming obscured in clouds/fog
this morning. Very light showers and sprinkles are already occurring
this morning and will continue at times mainly west of the mountains
and along the slopes. Heavier precipitation moves in from the NW to
the SE after 21Z this afternoon. Brief heavy rain will be possible
at all TAF sites west of the mountains between about 02 to 12Z late
this evening through Friday morning. The brief bursts of heavy rain
could bring visibility below 1SM and CIGS to 500 feet MSL. Winds
will be gusty this evening through Friday morning all areas, with
gusts around 25 knots for the coastal/valley areas, and up to 45
knots for the mountains and deserts slopes. Conditions will
gradually improve after 10-15Z Friday from NW to SE.
&&
.MARINE...
Mainly light and variable winds will prevail through this afternoon,
then winds will increase out of the south ahead of a significant
Pacific storm system this evening, then shifting to the west Friday
morning. Conditions will be hazardous for small craft during this
time, with wind gusts between 20 to 25 knots along with heavy rain
squalls and rough seas at times. The gusty westerly winds will
gradually weaken by Friday afternoon and the heavy rain showers will
also gradually taper off. The storm will then pass by Friday
afternoon, then a moderate onshore flow will continue, with
occasional light showers Saturday through Monday.
&&
.HYDROLOGY...
Lighter rainfall will continue into this afternoon. More
widespread rainfall fed by an atmospheric river will spread
southward across the area during the late afternoon and early
evening with rainfall becoming heavy at times for late tonight
into Friday morning with hourly rainfall up to 0.60 inch. A Flood
Watch remains in effect for tonight through Friday morning for all
areas.
Rain totals through Friday night:
Coastal and Valley Zones.....1.5 to 2.5 inches.
Mountains....................3 to 6 inches.
Deserts......................0.5 to 1.5 inches
The highest rain totals of 5 to 6 inches are most likely on the
southwest facing slopes of the San Bernardino County mountains.
Snow levels above 8000 feet will fall during the day on Friday to
around 6500 feet late in the day. Snow is most likely on the
highest peaks, above 8500 feet, with lighter snowfall possible
down to around 7500 feet.
A moist northwest flow pattern will remain across the area into
the middle of next week with additional periods of precipitation
likely, but with low confidence in the timing and amounts. The
next round of more widespread precipitation may arrive for
Saturday night into Sunday with snow levels lower and
precipitation amounts significantly less.
&&
.SKYWARN...
Skywarn activation may be requested for tonight into Friday
morning.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from this evening through Friday morning 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-San Gorgonio Pass Near Banning-
Santa Ana Mountains and Foothills.
Wind Advisory from 6 AM to 6 PM PST Friday for Riverside County
Mountains-San Bernardino County Mountains-San Diego County
Mountains.
Flood Watch from late tonight through Friday morning for Apple
and Lucerne Valleys-Coachella Valley-San Diego County
Deserts.
Winter Weather Advisory from midnight tonight to noon PST Friday
for San Bernardino County Mountains.
PZ...Small Craft Advisory from 6 PM this evening to noon PST Friday
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...BrothertonThe national radar mosaic for the moment the first event began.
17 heavy rain, 11 flood, 4 high wind, 1 heavy snow. Local standard time, as filed.
Trained spotter reports 1.5 inches of rain in Ramona.
Trained spotter has accumulated over 2 inches of rain since last night at 5pm. Also a few flashes of lightning and high winds.
Mesonet station PRMC1 Palomar Mountain reports 5.89 inches of rain in the past 24 hours.
Mesonet station MLGC1 Mt. Laguna observatory raws observes 2.93 inches of rainfall in the past 24 hours.
Mesonet FBOC1 reports 3.46 inches total of rain in the past 24 hours.
Public measures 1.75 inches of storm total rainfall in northeast Orange, CA.
Mesonet SDOC1 Silverado Canyon measures 2.87 inches of storm total rainfall.
Trained spotter reports 2.65 inches of storm total rainfall.
CoCoRaHS station ca-rv-78 in Corona measures 3.17 inches of rain in past 24 hours.
Mesonet station GW0529 in Ontario reports 3.59 inches of rain in the past 24 hours.
Mesonet RLOC1 Rialto reports 3.9 inches of rainfall in the past 24 hours.
Mesonet DVOC1 reports 6.19 inches of rain in past 24 hours.
Mesonet station 1877D wrightwood reports 4.38 inches of rain in the past 24 hours.
Mesonet MLFC1 Lytle Creek 7.66 storm total rainfall.
COOP observations station BBLC1 reports 6.03 inches total of rain in the past 24 hours.
Mesonet station UPSC1 upper Snow Creek reports 6.03 inches of rain in the past 24 hours.
Mesonet station BEUC1 in Beaumont reports 2.62 inches of rain in the past 24 hours.
Caltrans reports several vehicles stuck in the snow on State Route 38 near Rainbow Ln. 3 inches snow measured around 8,000 ft elevation.
Caltrans reports flooded roads with some vehicles stuck in water at the intersection of seminole drive and main street in cabazon.
El Toro road on-ramp to I-5 flooding. Vehicle stuck water.
Gusty winds occurred across the region with gusts over 50 MPH reported. 75 MPH wind report at Volcan Mountain.
Gusty winds occurred across the region with gusts over 50 MPH reported. 63 MPH wind report at Otay Mountain RAWS.
Gusty winds occurred across the region with reports over 50 MPH. Castle Rock Road station reported a 58 MPH wind gust.
Mesonet station Weatherflow XHTG Huntington Beach pier reports 59 MPH wind gust along line of heavy rainfall.
The 1st ave on ramp to Interstate 5 flooded. heavy shower occurred at 11 am.
Rocks in roadway per Caltrans CHP. Heavy rain reported at 8 am.
Green river road area had lanes closed on this road and on Highway 91 due to flooding. 2.76 inches rainfall at Corona past 24 hours and 2.4 inches at Prado dam.
Caltrans reported all lanes closed in both directions on Route 18 from upper waterman to mormon rock just below Route 138 due to boulders in the road and washed out roads. Highway 18 was closed in lower waterman canyon in the morning due to road partially washed out and guardrail hanging. Several gauges on Route 18 reported 5 to 6 inches rainfall past 24 hours.
Flooded hov lane 1 on highway 91. 2.5 inches of rain in this area past 24 hours.
Trained spotter report, 0.40 inch of rain from thunderstorm between 6:10 and 6:35 a.m. with moderate street flooding westside seal beach. 30 mph wind estimated.
Route 91 west and Route 241 south connector 2 lanes flooded with 2 feet of water.
Varner road flooding near Interstate 10. 0.5 to 1.0 inch rainfall in northern Coachella Valley.
Road closures include indian canyon from tramview to palm road springs station road, gene autry from interstate 10 to east via escuela, araby drive through wash, vista chino from gene autry to cathedral city, elm street from bonita ave to adele ave, and part of seminole drive. 0.5 to 1.5 inches of rainfall and 2 to 3 inches across surrounding foothills. 1 inch rainfall reported at Palm Springs Airport.
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, December 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: 998953, 998957, 998960, 998961, 998964, 998965, 998968, 998971, 998973, 998980, 998984, 998985, 999019, 999021, 999022, 999023, 999024, 999025, 999043, 999028, 998823, 998824, 998826, 998828, 999026, 999027, 999031, 999038, 999034, 999050, 999029, 999049, 999047.