Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 170912
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
212 AM PDT Wed May 17 2017

.SYNOPSIS...
A deep marine layer will remain in place west of the mountains
today. Gusty west winds will continue in the mountains and
deserts through the evening. Warmer Thursday through the weekend
under high pressure aloft and weak offshore flow. Onshore flow
returns next week to bring back coastal clouds.

&&

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

The coastal basin gradually filled with low clouds overnight,
with Orange County the last clear holdout. A coastal eddy has
developed and that will keep our marine layer healthy today, but
not quite as deep nor the clouds as extensive as they were
Tuesday. In fact, most areas ought to get a lot more sunshine this
afternoon. Strong onshore flow today is associated with a trough
of low pressure moving through the interior west. That feature
will produce some strong winds in parts of our mountains and
deserts, with top gusts exceeding 50 mph. Hence the wind advisory
through this evening. Although the coastal eddy continues tonight
into Thursday, the flow will turn offshore and disallow the full
extent of coastal clouds in the coastal basin. That will bring
even more sunshine Thursday and a meaningful start to a warming
trend. High pressure aloft combines with the offshore flow peaking
Friday morning to sweep away the coastal clouds and pressure the
air into warming up and drying out. Not a legit Santa Ana event,
but some spots below canyons will get brisk northeast winds.
Put away the jackets. Temperatures Friday will head into the 80s
for the valleys and into the 90s in the lower desert, then 90s and
100s respectively for the weekend. As the offshore flow relaxes
over the weekend, the warm and dry air mass continues and those
days should be the warmest inland in the coming week. Patchy
coastal clouds and fog will attempt to return. The upper air
pattern becomes rather non-descript, but finally somewhat May-
like (unlike the March-like weather we`ve been having). High
pressure aloft will dominate, but with a very weak hang-back
trough over the Southwest along with a weak cutoff low in the
Pacific to our southwest. These features will help bring back weak
onshore flow Monday and some clouds both high and low. A cooling
trend will begin at the coast and extend inland during the week,
along with the marine layer and some presence of the coastal
clouds nights and mornings. Quite seasonal for May.

&&

.AVIATION...
170900Z...Coast/Valleys...Low clouds, with bases 1800-3000 ft MSL
and tops to 5000 ft MSL, will continue inland through mid
morning. VIS of 1 SM or so will occur where low clouds interact
with higher terrain. Expect clearing to the coast later this
morning between 16Z and 18Z.

Desert Mountain Slopes/Deserts...West winds with gusts of 35-45 kt
will result in areas of mdt to strong up/downdrafts and LLWS over/E
of the mountains through this evening. Otherwise FEW clouds AOA
20000 FT MSL and unrestricted vis through early evening. Areas of
blowing dust and sand possible in the deserts this afternoon and
evening.

&&

.MARINE...
Northwest winds with occasional gusts of 25 kt in the outer waters
this afternoon and evening. No other hazardous marine weather is
expected through Saturday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 9 PM PDT this evening 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.

PZ...Small Craft Advisory for winds from 11 AM this morning to 10 PM
     PDT this evening for Waters from San Mateo point to the
     Mexican Border Extending 30 to 60 nm out including San
     Clemente Island.

&&

$$

PUBLIC...MM
AVIATION/MARINE...Brotherton



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