Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 262037
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
135 PM PDT Wed Apr 26 2017

.SYNOPSIS...
A deepening trough over the Great Basin and a strong ridge over the
eastern Pacific will bring gusty onshore winds at times through
Thursday. A Santa Ana pattern sets up on Friday with a period of
strong offshore winds Friday night and Saturday. Mostly sunny and
warm early next week with above average temperatures.

&&

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

Strong northwest flow between a deepening trough over the
intermountain west and a large eastern Pacific high will continue
for the next few days.

Strong northwest winds started surfacing in the San Bernardino
County mountains and deserts early this afternoon. Peak gusts
through 1 pm include 38 mph at Hesperia, 36 mph at Pinon Hills and
31 mph at Big Bear Airport. The wind event is just beginning with
the strongest winds surfacing this evening and spreading southeast
into the Riverside and San Diego County Mountains and deserts. 850
mb winds increase to 45-50 kt overnight with large subsidence
transporting wind energy toward the surface. A Wind Advisory is in
effect until 3 AM Thursday for the mountains and deserts for
sustained winds of 20-30 mph with gusts to 50-60 mph.

Orange County: Changes were made to increase the winds in northern
Orange County and parts of the IE the next two days.  Models show a
period of strong west winds surfacing this evening in northern
Orange County this evening and continuing overnight. The west winds
will be somewhat localized, not reaching southern Orange County or
San Diego County where winds will be lighter due to a coastal eddy
circulation tonight. On Thursday afternoon and evening a second
burst of low level winds is forecast over northern Orange County and
parts of the IE.

Friday and Saturday: The 12Z WRF and GFS runs are trending much
stronger with the offshore wind event. Initially, the northerly
winds will surface mainly from Cajon Pass into Orange County Friday
morning. Then on Friday night and Saturday the models are projecting
stronger and more widespread offshore winds in the mountains and
foothill, surfacing across all of Orange County and out over the
coastal waters of Orange County. Trends will continue to be
evaluated, but this is shaping up to be a moderately strong Santa
Ana Saturday in the mountains, foothills, inland valleys and Orange
County.

Temperatures with remain a little above average through the weekend.
The offshore flow will bring minor cooling to the mountains and
deserts, while downslope warming west of the mountains will bring
warming, especially to the Orange County coast on Saturday due to
the Santa Ana. The wind event weakens Saturday night with lighter
offshore winds Sunday.

Outlook for early next week: Quiet weather with seasonal
temperatures as the large upper ridge remains firmly anchored over
the eastern Pacific. Onshore flow will bring minor cooling to the
coastal areas, and warming to the mountains and deserts.

&&

.AVIATION...
261935Z...Coast/Valleys...P6SM vis and SCT-BKN clouds AOA 20000 ft
msl continuing through 27/0600 UTC. 27/0600-1600 UTC...patchy BKN
stratus probably developing over the coast and valleys, with bases
1500-2000 ft msl and tops around 2500-3000 ft msl. Also, strong
surface W to NW winds 15-20 kt gusting 30-35 kt possible over the
northern half of Orange county in the 27/0000-0900 UTC time-frame,
with llws possible where winds do not surface.

Mountains/Deserts...SCT-BKN cloud layers AOA 20000 ft MSL and P6SM
vis through Thursday morning. Strong W winds 20-30 kt with gusts 35-
50 kt developing along mountain ridges, desert slopes and wind-
favored adjacent desert areas will result in strong uddfs/llws over
and east of the mountains. Areas of blowing dust and sand possible
in the deserts resulting in possible vis AOB 5 sm.

&&

.MARINE...
Northwest winds over the outer waters will strengthen again this
evening, with gusts reaching 25 to occasionally 30 kt, and continue
at around this strength through late Friday night. In addition to
the winds, short-period seas will increase to 9-12 ft. A Small Craft
Advisory for the outer waters starts this evening and continues
through late Friday night.

For the inner waters, outer portions of that zone may get 25 kt
gusts by late Thursday afternoon, with more widespread strong winds
likely late Friday, along with steep seas. A Small Craft Advisory
for the inner waters starts 3 pm Thursday and continues through late
Friday night.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 3 AM PDT Thursday for Apple and Lucerne
     Valleys-Coachella Valley-Riverside County Mountains-San
     Bernardino County Mountains-San Diego County Deserts-San
     Diego County Mountains-San Gorgonio Pass Near Banning.

     Wind Advisory from 6 PM this evening to 9 AM PDT Thursday for
     Orange County Coastal Areas-Orange County Inland Areas.

PZ...Small Craft Advisory until 5 AM PDT Saturday for Waters from San
     Mateo point to the Mexican Border Extending 30 to 60 nm out
     including San Clemente Island.

     Small Craft Advisory from 3 PM Thursday to 5 AM PDT Saturday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm.
&&

$$

PUBLIC...Moede
AVIATION/MARINE...Harrison



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