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Forecast Discussion for San Diego, CA

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402
FXUS66 KSGX 250528
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
928 PM PST Tue Nov 24 2020

.SYNOPSIS...
Seasonally cool weather through Thursday will be followed by a Santa
Ana pattern Friday through Sunday that will bring sunny, warmer days
and clear, cool nights. Gusty northeast winds will begin Thursday in
the mountains and foothills, then lower into the valleys in the
afternoon and evening. The strongest winds will surface Thursday
night and Friday. The winds will be lighter over the weekend.


&&

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

Highlights:

* Seasonally cool Wednesday and Thursday with marine layer clouds
  returning.
* Gusty Santa Ana winds Thursday through Saturday, strongest Friday
  morning.
* Warmer days Saturday and Sunday with lighter winds. Very low
  humidity.

Update: The sky remains clear across the service area this
evening. Some low cloudiness could make a comeback late tonight
especially towards dawn Wednesday along the coast. Otherwise,
tranquil weather prevails. See previous discussion below for
forecast details.

Previous Discussion:

A strong trough moving into the Pacific Northwest this afternoon
will deepen and dig southeast across the Great Basin Wednesday.
Onshore flow ahead of this trough will bring a surge of low level
moisture and marine clouds back into the coastal zones and western
valleys tonight and tomorrow morning. Therefore, the usual diurnal
clearing back to the coast may be slowed by the increasing onshore
flow in the afternoon, and some areas within a few miles of the
coast may only see partial clearing tomorrow afternoon. The clouds
surge back inland Wednesday evening as the onshore gradients peak
ahead of the advancing trough.

The trough axis passes by early Wednesday night, and that sets the
stage for a Santa Ana wind event Thursday and Friday. The 12Z models
and their ensembles are a little faster and a little stronger with
the Santa Ana winds. Gusty northeast winds will initially surface in
the San Bernardino Mountains early Thursday, then strengthen and
expand into the Inland Empire and inland Orange County Thursday
afternoon. Winds in these areas will gust from 35-45 mph with peak
gusts of 50-60 mph in the wind prone passes and canyons like the
Cajon Pass and the passes in the Santa Ana Mountains. San Diego
County will be spared from this initial burst of winds, but the
easterly winds will increase later in the day with the strongest
winds arriving Thursday night into Friday. Weak to moderate strength
winds will continue Friday night into Saturday, followed by weaker
and more localized east winds Sunday and Monday.

A Fire Weather Watch was issued and will take effect on Thanksgiving
Day. It will run from 2 PM Thursday to 10 PM Friday in San
Bernardino, Riverside and Orange Counties. In San Diego County it
will start a little later, beginning at 9 PM Friday and going
through 2 PM Saturday.

After a cool day on Thanksgiving, there will be a steady increase in
temperatures Friday through Sunday, with the most notable warming
west of the mountains with downslope flow pushing temperatures into
the 80s Sunday. The warm, dry weather will continue into Monday
before turning a little cooler Tuesday and Wednesday.

&&

.AVIATION...
250430Z...Coast/Valleys...Weak offshore flow will help keep any low
clouds off the coast for most of the night. Patchy low clouds
possibly developing 12-16Z along the coast and up to 10 mi inland
with bases near 1500-2000 ft MSL. Most locations should become SCT
around 18-20Z, then clouds will begin to move back inland around
26/02-04Z with bases near 2500 ft MSL, spreading into the valleys
Wed night.

Mountains and Deserts...Mostly clear with unrestricted vis through
Wednesday evening.

&&

.MARINE...
No hazardous marine weather through Thursday afternoon. Gusty
northeast winds in excess of 20 kt may develop over portions of the
coastal waters at times Thursday evening through Friday morning.

&&

.FIRE WEATHER...
A Fire Weather Watch was issued and will take effect on Thanksgiving
Day. The Watch will be in effect from 2 PM Thursday to 10 PM Friday
in San Bernardino, Riverside and Orange Counties. In San Diego
County the Watch will start a little later, beginning at 9 PM Friday
and going through 2 PM Saturday. The Fire Weather Watches were
coordinated with the Oxnard office and with the Storm Prediction
Center Fire Weather Desk.

The northeast winds will start out in the San Bernardino County
Mountains Thursday morning, then strengthen and lower into the
Inland Empire and inland Orange County Thursday afternoon. The winds
will reach the San Diego County Mountains Thursday evening. The most
recent model output has forecasted the winds speeds to be 5 to 10
mph higher than the previous runs, and this has been reflected in
todays forecast. Peak gusts of 50 to 60 mph are likely in the most
wind prone areas of the back country, with a few gusts to 65 mph.

The most widespread and strongest winds will take place Thursday
night and Friday. Moderate strength winds will continue Friday night
into Saturday, strongest in the east-west passes of San Diego and
Riverside County, and a little weaker in San Bernardino County. The
winds will be weaker in all areas Sunday and Monday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Fire Weather Watch from Thursday evening through Saturday
     afternoon for San Diego County Inland Valleys-San Diego
     County Mountains-Including The Palomar And Descanso Ranger
     Districts of the Cleveland National Forest.

     Fire Weather Watch from Thursday afternoon through Friday
     evening 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 Gorgonio Pass Near Banning-Santa Ana Mountains-
     Including The Trabuco Ranger District of the Cleveland
     National Forest.

PZ...NONE.
&&

$$

PUBLIC...Gregoria (Update)/Previous Discussion (Moede)
AVIATION/MARINE...SS

Previous Forecast Discussions may be found at
NWS San Diego, CA (SGX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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