A frontal system accompanied by an atmospheric river moved into Southern California in the middle of December. This impacted the area by flooding and wind damage, as well as higher elevations receiving significant snowfall, where roads were impacted.
Every event with a place to put it; 12 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 frontal system accompanied by an atmospheric river moved into Southern California in the middle of December. This impacted the area by flooding and wind damage, as well as higher elevations receiving significant snowfall, where roads were impacted.
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 13, 9:40 PM PST, 2 hours 20 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
940 PM PST Mon Dec 13 2021
.SYNOPSIS...
A powerful winter storm will bring widespread rain, mountain
snow, and strong winds to Southern California Tuesday. The storm
will move out of the area Tuesday night followed by cool days and
cold nights Wednesday and Thursday. A weak weather system will bring
a small chance of showers west of the mountains Thursday night into
Friday.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
EVENING UPDATE:
The rain band associated with the Atmospheric River over Central
California this evening will sag south tonight and move across
Southern California Tuesday. At 9 PM the leading edge of the rain
band was moving across Santa Barbara County. Here are some of
the 12-hour rain totals ending at 9 PM:
Santa Barbara Airport.....0.32"
San Luis Obispo...........1.45"
Big Sur RAWS station......4.77"
To follow the southward progress of the rain band, here is a link
to the regional radar: https://go.usa.gov/xeHnZ
The band of heavier rain will move from northwest to southeast
across the area starting Tuesday morning, with a chance of
thunderstorms along and ahead of the cold front. Heavy snow will
impact the San Bernardino and Riverside County mountains. Snow
levels will start out above 7000 feet, dropping to 4500-5000 feet in
the late afternoon. More details on rain and snow amounts and
impacts can be found in the Hydrology section below.
Strong south winds ahead of the cold front will shift westerly with
CFP. The coastal and valley zones will be very windy with peak gusts
of 45 mph near the coast in the afternoon. Mountain and desert winds
will gust as high as 60-70 mph.
*From Previous Discussion*
The precipitation will end Tuesday night. Winds will be slower to
decrease, lingering into Wednesday morning. With clouds clearing and
winds dying down, patchy frost is expected to form in the inland
valleys each night through the weekend. Cool conditions will prevail
through the rest of the week. The next wave of energy is weak, but
seemingly sufficient for small chances of showers late Thursday into
Friday morning. On Friday we lose the clouds as offshore flow
develops. Some coastal clouds or fog could reappear by Sunday.
&&
.HYDROLOGY...
Isolated light showers will continue into tonight ahead of a
significant winter storm Tuesday. Widespread rain is expected for
much of the day tomorrow. Rain will be heavy at times, especially
along the coastal slopes of the mountains. After the front moves
through Tuesday afternoon, cold air behind the front will
destabilize the atmosphere, leading to a chance of thunderstorms.
All this rain, including bursts of heavier rain, will lead to
periods of urban flooding and possible debris flows and flash
flooding near and below recent burn scars, especially Apple, El
Dorado, and Bond burn scars, as well as elsewhere on steep terrain.
Rainfall rates west of the mountains could reach 0.50-0.60 inch per
hour Tuesday. Orographic forcing will be enhanced with the strong,
moist southerly flow heading into the San Bernardino Mountains.
Rainfall rates of 0.75 inches an hour expected on the coastal slopes
of the San Bernardino Mountains.
Current rainfall estimates are widespread 1-1.5 inch amounts west of
the mountains, 2-3 inches on the peninsular ranges, 2-6+ inches in
the San Bernardino Mountains, 0.10-0.50 inches in the low deserts,
0.50 to 1 inch in the High Desert. Highest rainfall totals in the
San Bernardino Mountains will be on the wetter south- facing slopes
of the San Bernardino Mountains, resulting in considerable runoff.
Rainfall could exceeding 1 inch in the high desert, which can cause
nuisance flooding where water is unable to drain properly on roadways
Total snow accumulations: 5 to 12 inches between 5,000 and 7,000
feet. Above 7,000 feet there will be locally higher amounts up to 3
feet in the Riverside County mountains and 3 to 4 feet in the San
Bernardino county mountains. Highest amounts will accumulate on the
highest peaks, above 8000 feet.
&&
.AVIATION...
140530Z...BKN/OVC CIGs 3000-5000 ft MSL will continue through
tonight for coastal/valley/mountain areas with increasing -SHRA and
mountain obscurations. Most vis below the cloud bases will be above
5 miles through 12Z Tue. SHRA with some SHSN in the mountains will
increase 12Z-19Z Tue, first near KSNA, KONT, KSBD 12Z-15Z then KSAN,
KCRQ 15Z-19Z with vis lowering to 1-3 miles and BKN/OVC CIGs falling
to 800-1500 ft MSL and widespread terrain obscurations. Isolated
thunder will be possible during the day Tuesday but overall risk is
too low to mention in the TAFs. Desert areas will have SCT SHRA
developing mostly after 18Z Tue with CIGs lowering to 2500-4500 ft
MSL and areas of vis 3-5 miles. All areas will have decreasing
precipitation Tue evening with CIGs mostly above 2500 ft MSL.
Strong winds will occur Tuesday into Tuesday evening, with
surface south winds 20-30 knots with gusts 30-45 knots in
coastal/valley areas, including KSAN/KCRQ/KSNA and 25-40 knots with
gusts 35-55 knots in the mountains and some desert slope locations,
but much more variable in the lower deserts, including KPSP/KTRM.
Winds will become west with similar speeds mainly after 19Z-22Z Tue,
decreasing gradually Tue evening. Strong up/downdrafts will occur
Tue through Tue evening.
&&
.MARINE...
Southerly winds will increase overnight through Tuesday morning
ahead of the next storm, becoming west-northwest Tuesday afternoon
after a cold front passes. Winds of 25 to 35 kts with gusts to 40
kts, combined seas 10-15 ft, and rough seas are likely, producing
hazardous boating conditions late tonight through Tuesday night. A
Gale
Warning remains in effect for 2 AM Tue-4 AM Wed to cover the period
of both small craft and gale conditions. With the cold front passage
late Tuesday morning through Tuesday afternoon, there is a slight
chance of thunderstorms and waterspouts.
&&
.BEACHES...
A High Surf Advisory has been issued for Tuesday/Wednesday. Expect
surf to rapidly build to 5 to 8 feet with sets to 10 feet beginning
Tuesday morning. Surf will lower Wednesday afternoon. There is also
a
slight chance of thunderstorms at the beaches Tuesday into Tuesday
evening.
&&
.SKYWARN...
Skywarn activation is requested Tuesday starting at 8 AM.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning from 4 AM Tuesday to 4 AM PST Wednesday for
Apple and Lucerne Valleys-San Diego County Deserts-San
Diego County Mountains.
Flood Watch from Tuesday morning through Tuesday evening for
Apple and Lucerne Valleys-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 4 AM Tuesday to 2 AM PST Wednesday for
Riverside County Mountains-San Bernardino County Mountains.
Wind Advisory from 4 AM Tuesday to midnight PST Tuesday night
for Coachella Valley-Orange County Coastal Areas-Orange
County Inland Areas-San Bernardino and Riverside County
Valleys-The Inland Empire-San Diego County Coastal Areas-
San Diego County Valleys-San Gorgonio Pass Near Banning-
Santa Ana Mountains and Foothills.
High Surf Advisory from 4 AM Tuesday to 2 PM PST Wednesday for
Orange County Coastal Areas-San Diego County Coastal Areas.
PZ...Gale Warning from 2 AM Tuesday to 4 AM 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.
&&
EVENING UPDATE...Moede
PUBLIC/HYDROLOGY...CO
AVIATION/MARINE/BEACHES...MaxwellThe San Diego radar (KNKX), 134 km away, was scanning. The volume nearest the first event began at 16:01 UTC.
7 flood, 6 high wind, 4 strong wind, 3 flash flood, 2 heavy snow, 1 heavy rain. Local standard time, as filed.
Park service measures 10 inches of snow at the top of the Palm Springs Tramway, elevation 8,400 feet.
Department of Highways reports 12 inches of new snowfall in Green Valley Lake.
High onshore winds occurred across the San Bernardino mountains. A wind gust of 85 MPH was reported at Silverwood Lake and an 84 MPH gust was reported at Heaps Peak near Lake Arrowhead.
Widespread wind gusts over 50 MPH occurred. Fremont Canyon RAWS reported a max wind gust of 66 MPH and Case Springs RAWS reported a max wind gust of 72 MPH.
Spotter reports one half inch pf rain since 6:00 a.m. Flooding was noted, which closed the Pacific Coast Highway from Warner to Goldenwest. Estimated wind gusts near 30 mph.
Spotter reports heavy rainfall in last two hours in Aliso Viejo area averaging about 0.6 per hour. In the last 30 minutes, heavier rainfall was reported and estimated to be closer to an inch per hour. Total interim rainfaill total is now 2 1/8 inch since start of storm.
Widespread wind gusts over 50 MPH reported. HPWREN station Boucher Hill on Palomar Mountain reports maximum wind gust of 77 MPH.
Widespread wind gusts over 45 MPH. Whitewater RAWS reported a peak wind gust of 61 MPH.
Large tree downed on Junipero Serra Road in San Juan Capistrano. Wind gusts 40 mph nearby sites. Widespread wind gusts occurred in southern inland Orange County.
Report from mPING: 1-inch tree limbs broken; shingles blown off. Wind gusts 40 to 45 mph in this area.
Reports of flooding on both highway on ramps of State Routes 133 and 73 off ramp. Rain rates of 0.40 to 0.50 inches and hour have fallen over the area with near an inch over the past 6 hours.
Vineland and Noble Streets in Beaumont area. 10+ foot long tree branches/trunks washing through as well and rocks larger than a foot round washing through the wash. Water flowing over 1 foot over crossing. Web cameras showing dark water flow and debris from Apple fire burn scar. Rainfall rates were as high as 0.60 per hour.
Flooding in the slow lane on Route 15 south and Route 94 near downtown San Diego. Area had rain rates of 0.60 inch an hour occurred.
A man and woman were swept into the San Diego river flood control channel in Mission Valley, near Murphy Canyon Road, attempting to rescue their dog. The heavy rain storm contributed to abnormally high and swift current in the channel.
Public reports large tree downed in Del Mar, uprooted near sidewalk. Wind reports in the area were near 40 MPH. Coastal San Diego County reported widespread peak wind gusts 35 to 45 MPH.
A tree fell in roadway on San Pablo Drive near Lake San Marcos. Wind gusts of 26 to 33 mph occurred in the area.
Law enforcement reports large tree down on truck on east side of Crestline. Wind reports near the area gusted near 50 MPH at the time.
State Highway 38 closed at Bryant street in Yucaipa to Lake Williams east of Big Bear due to rock and debris flows. Heavy rain occurred past few hours in the afternoon.
Tree on powerline. Wind gusts 50 to 70 mph in this area on Tuesday. Power outages occurred on Greenbriar Drive in Lake Arrowhead.
Law enforcement reports one lane of State Highway 78 at El Camino Real flooded.
Reported 6 debris flows in Bond Fire scar and 4 in Silverado Canyon. Santiago Creek Road blockage from high water flows and mud. Jackson Creek Road flooded with mud and debris. Rainfall rates of up to 1.2 inches reported at Irvine Lake and Santiago Canyon site.
The bottom of Interstate 805 south to Bonita Road exit offramp was flooded.
Heavy rain at St. Mark golf club reported on twitter. 1.34 inches of rainfall measured with pictures of flooded golf course and parking lots.
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: 996236, 996237, 996275, 996283, 998280, 998279, 996280, 996284, 996281, 996282, 998278, 998275, 996762, 996763, 996278, 996279, 996277, 998276, 996276, 996771, 998277, 996761, 996769.