A closed upper-level low pressure system made its way south over the waters off the Baja California coast to create a rare pattern of wet and offshore windy conditions across the region.
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 closed upper-level low pressure system made its way south over the waters off the Baja California coast to create a rare pattern of wet and offshore windy conditions across the region.
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 7, 1:49 PM PST, 2 hours 11 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
149 PM PST Mon Dec 7 2020
.SYNOPSIS...
Santa Ana winds will continue to increase with the strongest
winds expected to occur tonight into Tuesday. Weaker northeast
winds will continue into Wednesday with gusts mostly 35 mph or
less. Onshore flow may return for late Wednesday through Friday
spreading cooling inland and possibly bringing a return of night
and morning coastal low clouds and fog. Offshore flow may return
for the upcoming weekend.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
-Forecast Highlights-
* Santa Ana winds peak tonight through Tuesday morning
* Localized damaging winds possible mountains/inland valleys
The Santa Ana winds arrived early this morning and have been on
the increase today. Now seeing localized gusts topping 60 mph with
the peak gust so far at Hellhole Canyon/San Diego County at 65
mph.
The upper low moving southwest off Point Conception will continue
to move south-southwest. Extensive mid-high level cloudiness will
continue over our region to the east of this vigorous feature.
Easterly winds will increase this evening and along with an
offshore pressure gradient, the Santa Ana winds will crank up and
peak tonight through Tuesday morning. The Red Flag Warning and
High Wind Warning was unchanged today with critical fire weather
conditions and strong winds expected over the mountains and into
the valleys. Gusts of 50-60 mph expected and localized gusts to
around 70 mph will likely occur in the backcountry at wind-prone
sites such as Hellhole Canyon, Sill Hill, Freemont, etc. While
most hi-res guidance suggest the strong winds will remain over the
coastal mountain slopes, given the upper support there is some
concern for localized strong wind gusts into portions of the
valleys, particularly over portions of the Inland Empire and
eastern San Diego valleys, mainly along and east from Valley
Center, Ramona and Alpine.
The upper low will move east over northwest Mexico on Wednesday
while merging with a longwave trough. The offshore pressure
gradient will relax Tuesday afternoon through Wednesday, leading
to a relaxation of the wind. Still, gusty east winds will continue
in wind-prone locales through Wednesday morning but not as
widespread as tonight and peak gusts likely to near 40 mph.
A tranquil second half of the week is expected. GFS/EC ensembles
suggest upper ridging over the Pacific off the CA coast with an
upper trough over the Rockies. Shortwave energy this upcoming
weekend has trended more inland, lessening the concern for
additional Santa Anas this weekend. Will continue to monitor but
right now only weak offshore flow is expected along with warming
temps after mid week cooling.
The CFS/Climate Forecast System is suggesting a potential pattern
change as we move towards Christmas week, favoring above normal
precipitation for SoCal as upper troughing retrogrades and
provides perhaps an increasing chance for rain and mountain snow
across SoCal. Low confidence, but at least there is an indication
that this dry weather pattern may be coming to an end later this
month and as we head into 2021. Precipitation here would
certainly be a welcome sight!
&&
.AVIATION...
072130Z...Local gusts 30-40 kts are expected over the mountains and
passes and strong up/downdrafts west of the mountains. The winds
increase tonight into Tuesday, with gusts 45-55 kts at times. Gusts
at the terminal sites will not be as strong, however, gusts of 30-40
kts will be possible at KSBD/KONT this evening. Expect LLWS to be
prevalent at the coastal terminals (KSAN/KCRQ/KSNA) with surface
winds staying 5-10 kts but winds at the 2000 foot level gusting 25-
35 kts tonight and Tuesday morning. Patchy blowing dust is possible
west of the mountains, with isolated vis reduced 2-6SM at times
Tuesday.
&&
.MARINE...
Seas could briefly touch 10 feet over the far offshore waters
Tuesday night. Otherwise, no hazardous marine conditions are
expected through Friday.
&&
.BEACHES...
A long-period WNW swell will build tonight, peak Tuesday and
Wednesday, and gradually subside Thursday. This will bring high surf
and associated hazards. The highest surf will be over the southern
San Diego County beaches where sets of 8 to 10 feet are expected at
times. The High Surf Advisory start time has been pushed earlier to
06Z Tuesday.
&&
.FIRE WEATHER...
*Red Flag Warning in effect for the mountains and valleys,
including inland Orange County and the San Gorgonio Pass
Santa Ana winds are strengthening and will peak this evening
through Tuesday morning, impacting the coastal mountain slopes
into the valleys and through passes. Gusts of 50-60 mph are
expected with localized gusts to around 70 mph in the backcountry.
The winds will diminish some from north to south on Tuesday
afternoon with weaker and more localized winds continuing into
Wednesday morning. Lowest daytime humidity will be around 10
percent through Tuesday with poor overnight recovery. A Red Flag
Warning for strong gusty winds and low humidity remains in effect
into Tuesday evening for the mountains, valleys, inland Orange
County, and the San Gorgonio Pass. High confidence.
Onshore flow may return on Wednesday afternoon and spread cooling
and higher coastal humidity inland for Thursday and Friday.
Weak offshore flow may then return for next weekend. Moderate
confidence.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning from 10 PM this evening to 6 PM PST Tuesday
for San Diego County Mountains-San Diego County Valleys.
Red Flag Warning until 10 PM PST Tuesday for Orange County
Inland Areas-Riverside County Mountains-Including The San
Jacinto Ranger District Of The San Bernardino National
Forest-San Bernardino County Mountains-Including The
Mountain Top And Front Country Ranger Districts Of The San
Bernardino National Forest-San Bernardino and Riverside
County Valleys -The Inland Empire-San Diego County Inland
Valleys-San Diego County Mountains-Including The Palomar
And Descanso Ranger Districts of the Cleveland National
Forest-San Gorgonio Pass Near Banning-Santa Ana Mountains-
Including The Trabuco Ranger District of the Cleveland
National Forest.
High Wind Warning from 6 PM this evening to noon PST Tuesday for
Orange County Inland Areas-Riverside County Mountains-San
Bernardino County Mountains-San Bernardino and Riverside
County Valleys-The Inland Empire-San Gorgonio Pass Near
Banning-Santa Ana Mountains and Foothills.
High Surf Advisory from 10 PM this evening to 1 AM PST Friday
for San Diego County Coastal Areas.
High Surf Advisory from 10 PM this evening to 1 PM PST Thursday
for Orange County Coastal Areas.
PZ...NONE.
&&
PUBLIC...Gregoria
AVIATION/MARINE...MMThe national radar mosaic for the moment the first event began.
4 high wind. Local standard time, as filed.
Mesonet station HHCSD Hellhole Canyon (SDGE) measures wind gust of 81 MPH at approximately 6:30 PM on the 7th.
Mesonet station HP003 Toro Peak (HPWREN) measures wind gust of 69 MPH at approximately 10 PM on the 7th.
Mesonet station FRCC1 Fremont Canyon measures wind gust of 65 MPH at approximately 10:51 AM on the 8th.
Mesonet station SE700 Banning (SCE700) reports wind gust of 57 MPH at approximately 1:30 AM on the 8th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, December 2020
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: 933097, 933098, 933099, 933100.