High Wind in California, December 2 to 3, 2016

Area Forecast Discussion
National Weather Service San Diego CA
800 PM PST Thu Dec 1 2016

.SYNOPSIS...
Variable clouds this evening with a few sprinkles over
southwestern San Diego County. The precipitation ends by late
tonight with little accumulation. Strong offshore flow develops
late tonight and continues through Saturday. The greatest impacts
will be across Orange County to the Inland Empire and adjacent
mountain areas. Gusty northeast winds will begin to weaken late
Saturday. Warmer with lighter winds Sunday. Cooler early next week
with gusty west to northwest winds, mainly in the mountains and
adjacent desert areas.

&&

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

Partly cloudy to mostly cloudy over much of SOCAL this evening as
a low pressure trough tracks across the region from NW to SE. Over
portions of southwestern San Diego County, the trough is producing
enough forcing along with some low/mid level instability to
convect the boundary layer moisture and produce isolated light
sprinkles. Little or no accumulations are expected and the the
precip should end by late tonight as the trough axis moves to the
southeast and conditions become stable.

From previous discussion...
This trough moves to the southeast late tonight before deepening
to the southwest during the day Friday. A closed upper low develops
over northern Mexico by Saturday morning. Meanwhile, a strong
surface high will move into the Great Basin. With strong offshore
surface pressure gradients from San Diego to Tonopah of 13-15 mb
and north-northeast winds of 35-45 kt at about 5000 ft, this is
an ideal set-up for a widespread strong offshore wind event. With
the more northerly gradient, the winds are expected to be stronger
over Orange county, the Santa Ana mountains/foothills, Inland
Empire, and the coastal foothills of San Bernardino and Riverside
counties, and a High Wind Warning goes into effect late tonight
and continues through early Saturday afternoon, with winds of
20-40 mph and gusts of 60 mph and local 70+ mph likely.
Nevertheless, San Diego county will continue to see some strong
and gusty northeast to east winds as well, but not quite as strong
as areas farther north, so a Wind Advisory has been issued for the
the San Diego county valleys and mountains where gusts of 50 mph
and local 60 mph could occur. The Coachella Valley and San Diego
county deserts may see some downsloping strong winds from the
north to northeast as well, so a Wind Advisory has been issued for
those areas.

Winds will weaken late Saturday night into Sunday as the low moves
east-southeast and an upper level ridge moves in from the
northwest. Sunday will be a little warmer under fair skies, with
light winds.

The first half of next week will be cooler with variable
cloudiness under the influence of another trough of low pressure
that moves in from the northwest. This trough will also bring
northwest flow aloft enough to produce periods of gusty west to
northwest winds Mon and Tue, mainly in the mtns and adjacent
deserts. The European model shows the potential for some light
precip on Tue but at this time probabilities are too low to
include in the forecast.

&&

.AVIATION...
020330Z...Multiple low, mid and high SCT/BKN clouds decks this
evening, with a light shower possible in the mountains. Lowest decks
will have bases around 2500-3500 ft MSL this evening. NE surface
winds will strengthen tonight through Friday morning, with 30-40 kt
gusts expected in the vicinity in the Inland Empire and across
Orange County. Isolated gusts near 60 kt are expected along coastal
mountain slopes of Riverside, San Bernardino and Orange Counties,
along with strong up/downdrafts and areas of LLWS. Winds will
continue most of Friday, with slight decreases in wind speed by late
afternoon.

&&

.MARINE...
Strong Northeasterly winds will develop Friday, with winds gradually
decreasing late Friday night and Saturday. Northeast winds of 15-25
kt with gusts 30-35 kt are expected, mainly from San Clemente Island
northeast to San Mateo Point. A Small Craft Advisory is in effect
from 7 AM Friday through 10 AM Saturday. NW wind gusts near 20 kt
are possible on Monday as an upper-level disturbances moves across
the region.

&&

.FIRE WEATHER...
A strong offshore wind event will affect the region late tonight
through Saturday due to a strong surface high moving into the Great
Basin and strong north to northeast winds aloft. Strongest winds
Friday morning through Friday night will affect the San Bernardino,
Riverside and Santa Ana mountains and passes as well as the Inland
Empire and Orange County, including all the way to the coast. NNE
winds of 20-40 mph with gusts of 50-70 mph are expected in these
areas, with locally higher gusts possible. Winds will not be
quite as strong in San Diego County during this time, but gusts 40
to 50 mph and local gusts to 60 mph will be possible.

Humidities will lower to 10-20 percent Friday with mostly poor
recovery Friday night. Saturday will be a little warmer and so
widespread single digit to low teen humidities are likely.

Conditions will remain cool, with mountain highs in the 40s and 50s,
and lowland highs in the 60s and low 70s. While we have had two
recent rain events, we are getting information from the fire
agencies in Orange county and San Bernardino county that fuels are
still receptive to large fire growth. Highest fire weather threat
areas will be near the Santa Ana mountains/foothills and in the
western Inland Empire through and below the Cajon Pass. Therefore,
Red Flag Warnings have been issued for Inland Orange County, the
Santa Ana mountains/foothills, and Inland Empire for Fri-Sat and
a Fire Weather Watch for Sat for the San Bernardino county coastal
foothills and Cajon Pass (since humidity will be too high in that
area on Fri).

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 9 AM Friday to 2 PM PST Saturday for
     Coachella Valley-San Diego County Deserts-San Diego County
     Mountains-San Diego County Valleys-San Gorgonio Pass Near
     Banning.

     High Wind Warning from 3 AM Friday to 2 PM PST Saturday 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-Santa Ana Mountains and Foothills.

     Red Flag Warning from noon Friday to 6 PM PST Saturday for
     Orange County Inland Areas-San Bernardino and Riverside
     County Valleys  -The Inland Empire-Santa Ana Mountains-
     Including The Trabuco Ranger District of the Cleveland
     National Forest.

     Fire Weather Watch from Saturday morning through Saturday
     afternoon for San Bernardino County Mountains-Including The
     Mountain Top And Front Country Ranger Districts Of The San
     Bernardino National Forest.

PZ...Small Craft Advisory from 7 AM Friday to 10 AM PST Saturday 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...PG
AVIATION/MARINE...JJT