Offshore flow produced Santa Ana winds and cold nights across wind-sheltered locations.
Every event with a place to put it; 3 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.
Offshore flow produced Santa Ana winds and cold nights across wind-sheltered locations.
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 16, 9:30 PM PST, 2 hours 30 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Thu Dec 16 2021
.SYNOPSIS...
Scattered light showers will continue this evening into early
tomorrow morning. Offshore flow will develop Friday, with weak to
locally moderate Santa Ana winds, strongest across the mountains in
San Bernardino and Orange Counties. Dry weather and slightly warmer
for this weekend. Onshore flow will develop early next week, and
chances for precipitation will return through the middle of the week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Evening update:
No changes to the forecast were made this evening. Light showers
have spread across the coastal and valley areas this evening and
will continue through late this evening. Rain amounts will be very
light with this activity, mainly around one-tenth of an inch or
less. Showers will diminish before sunrise on Friday.
Thursday afternoon discussion:
Longwave troughing will be replaced with ridging Friday through this
weekend, allowing for slightly warmer temperatures and offshore flow
to develop. Winds will increase early Friday morning across the San
Bernardino Mountains and Orange County Mountains, and will expand
farther south through the morning. The strongest Santa Ana winds
will occur across the mountains and wind-prone passes, where gusts
of 45 to 50 mph will be possible. Winds will diminish Saturday
morning, and fair and dry conditions are expected through the
weekend.
An intense low pressure system will begin to develop off the coast
of the Pacific Northwest Sunday into Monday. Differences exist in
the strength and location of this system, with the 12z GEFS showing
the center closer to shore and slightly stronger than the 12Z ECMWF
EPS. This will have an impact on our temperature outlook next week;
the GEFS solution would suggest lower temperatures.
Regardless, moisture will increase across the West Coast.
Considerable spread exist for the placement and strength of the
atmospheric river, with the 12z GEFS IVT suggesting the AR to be
centered over Southern California and northern Mexico as early as
Tuesday evening through Thursday, with the 12Z ECMWF IVT Wednesday
morning into Friday. Confidence on timing and intensity of this
precipitation is lower because of these reasons, but it does seem
like the region could get measurable precipitation by the middle or
end of next week.
&&
.AVIATION...
170425Z...Coast and Valleys...BKN-OVC010-030 with vis reduced to 2-4
miles in areas of -RA and FG through 12Z Friday. Clearing 12-15Z.
After 15Z...gusty north to northeast winds and moderate
up/downdrafts/LLWS west of the mtns, possibly impacting KSBD, KONT
and KSNA.
Mountains and Deserts...SCT-BKN200 tonight and Friday.
&&
.MARINE...
No hazardous marine weather is expected through Tuesday.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 3 AM Friday to 4 AM PST Saturday for San
Bernardino County Mountains-San Gorgonio Pass Near Banning-
Santa Ana Mountains and Foothills.
PZ...NONE.
&&
PUBLIC...Schenk/JMB
AVIATION/MARINE...MoedeThe national radar mosaic for the moment the first event began.
2 frost/freeze, 1 high wind. Local standard time, as filed.
Cold nights occurred with temperatures lowering to 25-30 degrees.
Cold nights occurred with temperatures lowering to 25-30 degrees.
Gusty Santa Ana winds occurred along the coastal slopes of the San Bernardino Mountains and below the Cajon Pass with widespread gusts over 45 MPH.
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: 998819, 998820, 998821.