Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 070440
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
840 PM PST Wed Dec 6 2017

.SYNOPSIS...
Santa Ana Winds will be strong at times through Saturday, with
the strongest winds likely on Thursday. Very dry conditions will
prevail under mostly clear skies. There will be a warming trend
through the end of the week, with above normal temperatures each
day. Offshore flow will continue next week continuing the dry
and warm days with no prospect for rain.

&&

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

We are tracking the shortwave diving south across the Great Basin
this evening and the subsidence noted with it in water vapor
imagery. The models are handling it well, so the forecast is on
track for increasing E-NE winds this evening, peaking tomorrow as it
passes south across Sonora Mexico. The 00Z sounding had a sharp
increase in the NE winds between 7K and 10K FT. This will provide
support to drive some mtn wave activity farther west off the
foothills at times. Red Flag and High Wind Warnings remain in
effect. Surface pressure gradients were holding near 15 MBS offshore
from SW NV and were about neutral to the lower deserts. The
gradient from the lower deserts will jump on Thu as the wave
drops south, helping to drive stronger east winds into San Diego
County.

Through 8 PM PST winds were increasing. Peak gusts of 70+ MPH were
reported at Fremont Canyon, and 60+ in spots on the San Diego County
coastal mtn slopes. The strongest wind potential exists between
Midnight and 2 PM Tuesday.

From previous discussion...

An upper-level trough moving by to our east tonight, combined with
surface offshore flow from the surface high over the Great Basin,
will create another round of strong east to northeast winds across
southwest CA tonight into Thursday. San Diego county will be the
main focus this time, with wind gusts along the coastal mountain
slopes and foothills forecast to be around 60 mph, and isolated
gusts around Sill Hill to near 90 mph. Winds will weaken Thursday
night into Friday, but remain strong. The High Wind Warning
remains in effect for the mountains, valleys and coastal Orange
County through Friday afternoon. The extremely dry airmass over
the area will continue afternoon relative humidity of 5-10% for
inland areas through next week. The ridge that is locked in over
CA for the time being will continue above normal high temperatures
for most areas through Thursday, with areas increasing to 5-15
degrees above normal this weekend into early next week.

The ridge will weaken and shift more westward by the middle of
next week, however above normal high temperatures, offshore flow
and the dry airmass is expected to continue through the period at
this time.

&&

.AVIATION...
070420Z...NE to E winds will strengthen to 30-40 kt with gusts
45-60 kt along the coastal mountain slopes/foothills and through and
below the passes and canyons overnight...resulting in STG-SVR
UDDFS/LLWS and possible rotors over and W or SW of the mountains.
Winds will peak mid-morning Thursday before slowly weakening through
the afternoon. Local vis 3-6 SM in BLDU possible in the wind prone
areas. Otherwise clear with unrestricted vis through Thursday
evening.

&&

.MARINE...
Offshore flow will strengthen again tonight and Thursday, with 25 to
30 kt east winds possible across portions of the coastal
waters. A Small Craft Advisory will be in effect from 10 PM this
evening through 10 PM Thursday. No additional marine hazards are
expected Friday through Monday.

&&

.FIRE WEATHER...
A Red Flag Warning remains in effect through 8 PM PST Saturday
as strong easterly winds and low RH prevail through the period.
Stronger winds are expected tonight through Thursday, especially for
portions of San Diego county which may see isolated gusts near 90
mph. Strongest winds will be below mountain passes and canyons, and
along the coastal slopes and foothills. Winds will begin to
drop off Thursday night but remain strong enough for Red Flag
conditions in these areas through Friday. Winds will weaken
further on Saturday, but RH will remain critically low, and
gusty offshore flow will continue along the coastal slopes and
foothills. Temperatures will be on the rise as well with highs in
the upper 70s and 80s for the inland valleys.

Only modest improvements are expected early next week in this Santa
Ana condition with offshore flow, low RH, and above average high
temperatures continuing.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning until 4 PM PST Friday 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 Diego
     County Mountains-San Diego County Valleys-San Gorgonio Pass
     Near Banning-Santa Ana Mountains and Foothills.

     Red Flag Warning until 8 PM PST Saturday 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.

PZ...Small Craft Advisory from 10 PM this evening to 10 PM PST
     Thursday 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...JAD/JJT
AVIATION/MARINE...SS



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