Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 052157
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
200 PM PST Tue Dec 5 2017

.SYNOPSIS...
Santa Ana Winds will bring strong northeast to east winds at times
through Saturday, with strongest winds likely Thursday. Very dry
conditions wlll prevail under mostly clear skies. There will be a
warming trend through Thursday, with daytime temperatures above
normal starting Wednesday. Offshore flow will continue next week and
bring more warm days and keep rain far away.

&&

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

Except for some high clouds over San Diego County, skies were clear.
Some smoke can be seen by satellite from the recent fire that
started northwest of San Bernardino, the Little Mountain Fire.
Strong gusty winds were impacting some areas, including
gusts to 80 MPH at Fremont Canyon this morning, and some
gusts over 50 MPH even in well-populated areas in the Inland Empire.
Winds were somewhat less strong in San Diego County, though Sill
Hill, in the Cuyamaca Mountains, had a gust of 59 MPH. These winds
will fluctuate some, and some areas have had decreases in wind
speeds, and winds should trend down some the rest of this afternoon
and tonight. Humidities will be low most everywhere this afternoon,
with minimums 15 percent or less in many places, some below 10
percent.

Upper level low was over southern California with the strongest
support for winds just north and west of the low where northeast
flow aloft was occurring. This low will be over Arizona tonight,
with some decrease in the height and MSLP gradients. Winds will be
somewhat weaker tonight and Wednesday, and even somewhat of a sea
breeze could occur Wednesday afternoon. Trajectories were
calculated, and most of the smoke from the LA/Ventura County fires
will likely stay off the coast, but if more fires develop/expand
farther east, then smoke will be more of a concern, especially
downwind along the coast. A strong ridge will develop over the West
Coast the next few days and place us under north flow aloft with
strong height gradients and cold air advection. A shortwave will
dive south between the upper low over the central US and the West
Coast ridge Wednesday night, with enhanced offshore flow behind the
wave. With the stable layer now a little below some of the mountain
crests rising to mostly above 700 MB, and increasing winds in the
stable layer, conditions will be favorable for strong mountain waves
Thursday, in addition to strong MSLP gradients, possibly around 15
MB from Tonopah, NV to San Diego, which will help more widely
distribute the wind, probably to some coastal areas even in San
Diego County. Local gusts could easily exceed 80 MPH, maybe even
approaching 100 MPH at extreme locations like Sill Hill, with some
populated areas having gusts around 60 MPH. Winds weaken slightly
Friday, but gusts could still top 60 MPH then in windy locations,
and the High Wind Warning has been extended through 4 PM Friday.
Winds steadily decrease Saturday and Sunday, and by Sunday, the
impact of the winds should be minimal, though offshore flow will
continue.

There is high confidence of the West Coast ridge and eastern North
America trough continuing much of next week, which will bring fair
dry weather, and with surface high pressure over the Great Basin,
there could be periods of offshore flow. Dry weather is pretty much
certain through at least the end of next week (16 Dec), and probably
beyond.

&&

.AVIATION...
052112Z...Strong E to NE winds 20-30 kt (gusting 40-50 kt and
locally 60 kt or greater) in the windier coastal slope, valley and
coastal areas, will result in strong UDDFS/LLWS and possible rotors
over and W or SW of the mountains through Wednesday morning. Blowing
dust may reduce VIS to 3-6 SM at times in the windiest locations.
KONT, KSNA, and KSBD likely to see gusty, sometimes strong, NE
surface winds through Wednesday morning, with LLWS likely if winds
happen to weaken. KCRQ and KSAN likely to have LLWS this evening or
early Wednesday morning but strong surface winds unlikely.
Otherwise, FEW-SCT clouds AOA 20000 ft msl becoming SKC by 06/0000
UTC and prevailing P6SM vis through Wednesday morning.

&&

.MARINE...
Although the offshore winds will diminish this afternoon, hi-res
model guidance shows that winds will pick up again in the northern
half of the San Diego county waters this evening, so the Small Craft
Advisory continues through late tonight. Offshore flow will continue
with gusty and intermittent easterly winds through Thursday, with
another potential hazardous small craft condition period occurring
Thursday with wind gusts up to 30 kt possible.

&&

.FIRE WEATHER...
Numerous areas have dew points in the teens and sustained winds of
25 MPH or greater, verifying the Red Flag Warning. Strongest winds
are in the Santa Ana Mountains and Foothills and from near Cajon
Pass into the Inland Empire. These winds will decrease slightly
late this afternoon through Wednesday, but with continued critical
fire weather conditions. Winds will strengthen again over the region
Wednesday night and Thursday with gusts over 80 MPH possible in some
locations just downwind from mountain crests. Strong winds will
likely also reach some coastal areas, including in northern San
Diego County Thursday. We will likely extend the Red Flag Warning
through Saturday as Friday will have strong easterly winds with
gusts locally exceeding 60 MPH, and Saturday will likely have
sustained local winds over 25 MPH and gusts over 35 MPH for 6 hours
or more, mainly in San Diego County. Based on current guidance,
winds should finally be below Red Flag criteria Sunday. Minimum
humidities will be at or below 15 percent (some areas below 10
percent) today and mostly below 10 percent each day Wednesday
through at least Saturday, with low humidities likely continuing
next week.

&&

.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 6 PM PST Saturday for 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.

     Red Flag Warning until 8 PM PST Friday 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 Gorgonio Pass Near Banning-Santa Ana Mountains-
     Including The Trabuco Ranger District of the Cleveland
     National Forest.

PZ...Small Craft Advisory until 1 AM PST Wednesday 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...Harrison



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