Wildfire and High Wind in California, December 1 to 12, 2020

Area Forecast Discussion
National Weather Service San Diego CA
151 PM PST Tue Dec 1 2020

.SYNOPSIS...
A moderate to strong Santa Ana wind will impact Southern
California Wednesday evening through Saturday, resulting in an
extended period of widespread, critical fire weather conditions
over the mountains and inland valleys. Localized damaging winds
are possible late Wednesday night through Friday morning. A dry
Santa Ana weather pattern will continue early next week as well,
but of lesser intensity. Dry weather conditions and above normal
temperatures are favored through at least the first half of
December.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

-Forecast Highlights-

* Moderate to strong Santa Ana Winds to impact the mountains and
  valleys Wednesday evening through Saturday
* Damaging winds possible late Wednesday night-Friday morning
* Dry Santa Ana pattern favored through at least next week

The storm track is all the way up into Canada and Alaska with a
blocking upper ridge over the West Coast and upper shortwave
energy diving southward across the Rockies and into the Desert
Southwest. This pattern sets up Santa Ana conditions across SoCal
and this looks to continue through next week and potentially
beyond.

Weak Santa Ana winds will continue across through Wednesday with
near critical fire weather conditions occurring below passes,
especially below the Cajon Pass, but the stronger winds hold off
until Wednesday evening.

A longwave upper trough elongated west to east will move
southward over the Rockies and into the Desert Southwest Thu-Fri
then into NW Mexico. Some models (EC) break this into a closed low
just south of our region. Strong surface high pressure will build
south into the Great Basin behind this feature, even nosing into
SE California. This will set up a tight thermal gradient along
with good upper support to generate a moderate to strong Santa
Ana wind event. The strongest winds look to occur Wednesday night
through Thursday morning with another increase in winds Thursday
night into Friday morning. Models show good upper support so we
could see fairly widespread wind gusts in the 30-50 mph range with
some gusts around 60 mph over the mountains and valleys. Even very
localized wind gusts up to 80 mph are possible at rural Santa
Ana wind-prone coastal mountain slope and foothill locations such
as Sill Hill and Freemont Canyon. Winds will be northeasterly
Wednesday night going more easterly Thu-Fri, favoring strongest
winds over San Diego County.

Winds will weaken Friday afternoon through Saturday but still will
be quite gusty of weak to moderate strength. Weak Santa Ana winds
will continue early next week and we could even see another uptick
in winds by next Tue or Wed. So we are stuck in this dry weather
pattern which does not bode well for fire weather concerns. See
Fire Weather discussion below. Temperatures will run slightly
above normal with mild/lukewarm days west of the mountains and
lower deserts but chilly nights, especially in wind protected
areas. Where the wind is blowing stronger, temps will stay higher
but the wind will add a bite at night. The high deserts will see
the coldest air Friday morning with widespread lows in the 20s
forecast. Slow warming will occur this weekend into early next
week.

&&

.AVIATION...
012115Z...Clear with unrestricted vis through tonight into
Wednesday. Locally gusty northeast winds of 15-25 kt will continue
through tonight and Wednesday in parts of the passes and foothills.

&&

.MARINE...
Breezy east/northeast winds with gusts 20-25 kt possible Thursday
and Friday near the coast and out into portions of the coastal/outer
waters. A long period west-northwest swell near 18 seconds will lead
to 6-8 foot swell Friday into early Saturday morning for areas south
of San Clemente Island.

&&

.Beaches...
Elevated surf is possible Thursday and Friday, highest in southern
San Diego County. Sets near 6 feet (locally higher) will be possible
along with a strong rip current risk.

&&

.FIRE WEATHER...

* Red Flag Warning in effect for the mountains and valleys
  Wednesday evening through Saturday evening

A moderate to strong Santa Ana wind will impact the mountains and
valleys Wednesday evening through Saturday. The strongest winds
will occur late Wednesday night through Friday morning. We likely
will see two peaks - one towards dawn Thursday and another
Thursday night. Still strong winds in between and with extremely
dry air this will create widespread critical fire weather
conditions lasting through at least Saturday. Winds will relax
later Friday through Saturday, but still areas of critical fire
weather conditions are anticipated.

Santa Ana conditions aren't leaving anytime soon. Next week will
continue with offshore winds and very dry air along with at least
weak Santa Ana winds. We could see another uptick in winds by next
Tuesday or Wednesday.

The latest models today support stronger winds for late Wednesday
night through Friday morning. This is why a High Wind Watch was
issued for the mountains and valleys. Widespread northeast to east
wind gusts of 30-50 mph are possible locally to 60 mph. Even very
localized wind gusts up to 80 mph are possible at rural Santa
Ana wind-prone coastal mountain slope and foothill locations such
as Sill Hill and Freemont Canyon.

No rain is forecast through at least December 10th.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 6 PM Wednesday to 10 PM PST Saturday 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 Watch from late Wednesday night through Friday morning
     for Orange County Inland Areas-Riverside County Mountains-
     San Bernardino County Mountains-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Mountains-San Diego County Valleys-San Gorgonio Pass Near
     Banning-Santa Ana Mountains and Foothills.

PZ...NONE.
&&

PUBLIC...Gregoria
AVIATION/MARINE...APR