A strong upper level trough swept through the Rockies on the 3rd of December, ushering a strong surface high into the Great Basin. The high peaked at 1048 mb on the 7th and brought a prolonged period of strong Santa Ana Winds and very dry weather to Southern California.
Every event with a place to put it; 10 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 strong upper level trough swept through the Rockies on the 3rd of December, ushering a strong surface high into the Great Basin. The high peaked at 1048 mb on the 7th and brought a prolonged period of strong Santa Ana Winds and very dry weather to Southern California. The most intense winds occurred on the 7th. The Lilac Fire began on the 7th near Interstate 15, and spread rapidly through the San Luis Rey River Basin near Bonsall. Damage to trees and power lines also occurred, along with some road closures.
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 4, 2:00 PM PST, 6 hours earlier.
Area Forecast Discussion
National Weather Service San Diego CA
200 PM PST Mon Dec 4 2017
.SYNOPSIS...
Santa Ana winds will occur at times this week bringing areas of
strong gusty northeasterly winds and very low humidity. Strongest
winds will be tonight and early Tuesday, then again Thursday. The
winds will very gradually decrease by next weekend, but humidity
will remain very low through early next week. Otherwise, mostly
clear skies will prevail with daytime temperatures above normal in
most areas starting Tuesday, continuing through early next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Areas of strong winds occurred north of San Diego County, with
strongest winds in the Santa Ana Mountains and below Cajon Pass.
Fremont Canyon in Orange County had a gust of 59 MPH around 9 AM,
and closer to more populated areas, Cal-State San Bernardino had a
gust of 47 MPH. Winds will not reach most of San Diego County until
tonight. Otherwise, high clouds prevailed with low-elevation
temperatures mostly in the 60s to lower 70s.
Strong surface high pressure will continue to build over the Great
Basin and continue through the rest of the week. The MSLP gradients
will be strongest Tuesday morning, with all models showing 19-20 MB
offshore flow from Tonopah to San Diego with a secondary peak of 14-
15 MB Thursday morning. Almost all of the support is near the
surface through Tuesday, with deepening of the northeast winds and
the stable layer lifting above mountain crests Wednesday/Thursday.
Mountain wave activity will be moderate through Wednesday but with
strong gap wind support through canyons/passes, then mountain wave
activity will be strongest Thursday, so the winds Tuesday will be
rather widespread but with peak winds mostly 70 MPH or less just
downwind from mountain crests and below Cajon Pass, but Thursday
could have strong mountain waves with peak winds possibly over 80
MPH but with a little less widespread strong winds. With a short
wave moving through Tuesday night, that should be a temporary
decrease in the winds then before the short wave shifts southeast of
the area by Wednesday night to bring that next push of the northeast
winds. Winds may still be strong in mountain wave prone areas
Friday, but should weaken gradually over the weekend. It will be
warmer the next several days, with a more notable warming trend
after the trough moves to the southeast Thursday. We could have a
lot of 80s in the valleys and even some coastal areas Thursday.
It appears that the west coast ridge will be quite strong through at
least early next week, and probably beyond that, while a deep
longwave trough covers eastern North America. This will make it
unlikely for us to have any precipitation for the next 10-14 days,
which could result in this fall (calendar dates) being tied for the
second driest fall in history, at least at San Diego International
Airport, after 1929. Our current total is 0.02".
&&
.AVIATION...
042100Z...East to northeast wind gusts of 20-35 kt will continue for
areas of the coasts and valleys which are near mountain slopes and
below mountain passes. Gusts will increase tonight to 45-55 kt as
offshore pressure gradients strengthen. Strong up/downdrafts are
possible near and in lee of higher terrain, along with LLWS before
and after winds surface. Blowing dust may reduce VIS to 3-6 SM at
times in the windiest locations. No stratus is expected tonight.
&&
.MARINE...
Offshore flow will increase this afternoon and produce northeast
wind gusts to 30 kt, mainly east of San Clemente Island. A Small
Craft Advisory remains in effect from late this afternoon through
Tuesday morning. No additional hazardous marine weather is forecast
Tuesday afternoon through Friday.
&&
.FIRE WEATHER...
For today through Thursday...surface high pressure over the Great
Basin will bring a prolonged period of moderate to strong Santa
Ana winds and very low humidities with a Red Flag Warning in effect
for all areas except the deserts. Lowest daytime humidities will
fall to 5 to 10 percent with poor overnight recovery. Areas of
northeast winds 20 to 30 mph with gusts to 55 mph and isolated gusts
over 65 mph are expected. Stronger and more widespread winds are
expected late night and Tuesday morning...and again late Wednesday
night into Thursday. Winds will be slightly weaker Friday, but the
combination of wind and humidity will likely continue the critical
fire weather conditions then. Winds will gradually decrease next
weekend, but humidity will remain quite low and result in elevated
fire weather conditions.
&&
.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 midnight tonight to 4 PM PST Thursday for
San Diego County Mountains-San Diego County Valleys.
Red Flag Warning until midnight PST Thursday night for Orange
County Coastal Areas-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 Coastal Areas-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 until 4 PM PST Thursday 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 Gorgonio
Pass Near Banning-Santa Ana Mountains and Foothills.
PZ...Small Craft Advisory from 4 PM this afternoon to 10 AM PST
Tuesday 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/FIRE WEATHER...Maxwell
AVIATION/MARINE...JJTThe national radar mosaic for the moment the first event began.
8 high wind, 1 strong wind, 1 wildfire. Local standard time, as filed.
Report of a large tree downed by strong winds in Orange, CA. Tree damage, minor roof damage, and an exploding transformer were also occurred in Santa Ana.
Fremont Canyon reported wind gusts over 70 mph for 13 hours, with sustained winds over 40 mph. A peak gust of 80 mph occurred 0751 PST and 0951 PST. Winds gusts over 70 mph were also reported at Pleasants Peak.
Strong winds below the Cajon Pass downed numerous trees and power lines, toppled 8-12 big rigs and lofted debris onto highways. Most of the toppled big rigs occurred near the Interstate 15-210 interchange. Two small wildfires also occurred along the 215.
Three mesonet stations near the Pala Indian Reservation reported peak gusts between 64 and 69 mph, with the peak gust occurring at Palomar Launch between 1015 and 1030 PST. Similar gusts impacted southern San Diego County with a peak of 70 mph at an SDG&E gauge along East Willows Rd. Tree damage was reported in El Cajon, with both trees and power lines down in Ramona.
Winds gusts in the 50-70 mph range were reported throughout the San Diego County Mountains. The strongest winds were at Sill Hill where winds gusted over 70 mph for 12 hours (0600 to 1900 PST), with a peak gust of 88 mph. A section of Interstate 8 through the Cleveland National Forest was closed to High profile vehicles. A big rig and trailer were blown over near the intersection of Interstate 8 and Hwy 79.
The Heaps Peak mesonet station reported wind gusts above 50 mph for 10 hours with a peak gust of 64 mph. A large tree fell along state route 38 near Barton Flats.
Peak wind gusts across the Inland Empire were mostly in the 30-40 mph range. Stronger gusts occurred below the Cajon Pass (with peak a gust of 55 mph at Ontario International) and the San Gorgonio Pass with a peak gust of 65 mph at Highland Springs Raws. The peak gust at Highland Springs occurred between 1316 and 1416 PST. Some tree damage occurred in Hemet. Small brush fires occurred near Murrieta and Mira Loma.
Winds downed several large trees in Carlsbad, La Mesa and National City. A man was killed in Carlsbad when a large tree branch fell on him. Light poles were also knocked down in Carlsbad and Tierrasanta.
The Lilac Fire began on the 7th near Interstate 15, and spread rapidly through the San Luis Rey River Basin near Bonsall. The fire consumed 4,100 acres, destroyed 157 structures and damaged 64. Over 100,000 residents were forced to or advised to evacuate and 20,000 people lost power. The fire was fanned by sub 10% relative humidity values and wind gusts over 50 mph. The fire was 100% contained on December 16th, but the majority of damage occurred in the first 48 hours. Damage value is an estimate.
Fremont Canyon reported wind gusts above 70 mph for 3 hours. Sustained winds were as high as 63 mph.
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 |
|---|---|---|---|---|---|
| Strong Wind, San Diego County Coastal Areas | 2017-12-07 | 70 | Male | Under Tree | Indirect |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2017Every state in 2017This day in weather historyWarnings in California, December 2017
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: 730810, 730808, 730811, 731494, 731495, 730814, 730816, 731493, 731496, 730820.