Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 241620
AFDSGX

AREA FORECAST DISCUSSION
National Weather Service San Diego CA
920 AM PDT SUN JUL 24 2016

.SYNOPSIS...
The cooling that began Saturday will continue today, with the
greatest cooling in the western valleys. Continued seasonally warm to
hot inland as easterly flow aloft brings periods of mid and high
clouds at times. As we move through the week, clouds may build over
the mountains in the afternoons, but moisture will be limited, along
with the chance for any showers and thunderstorms. A little cooler
next weekend into the first part of August as another trough develops
along the West Coast.

&&

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

Marine stratus was limited to coastal areas of San Diego County early
this morning. At 8:30 AM PDT satellite imagery showed the farthest
inland extent at about 15 miles over SW San Diego County, and almost
none into Orange County. The Miramar sounding had only a slight
deepening of the marine layer over yesterday morning, with a 9
degree C inversion base near 950 FT. Winds were generally south up
through 12K FT. There was some very weak instability above 20K FT
and PW was up to 1.17 inch from 0.81 inch yesterday. Surface
pressure gradients showed weak 24 HR onshore trends. Values ranged
from 1-3 MBS onshore to the deserts.

The coastal eddy circulation was centered well offshore this morning,
but south winds were still brisk along the immediate coast with some
spots gusting at 15-18 MPH. Gusty winds up to 25 MPH from the SE were
also reported from the Coachella Valley, where a gulf surge was
ongoing, pushing high dewpoints into the region. this may shave a few
more degrees from the high temps in the Coachella Valley today.

Otherwise...No forecast changes are expected this morning. It will be
cooler in the valleys, and any thunderstorm probabilities look slim
over the mts and deserts, despite the modest moisture and instability
increase.

From previous discussion...

High pressure aloft will weaken slightly through Monday...
strengthen slightly for Tuesday through Thursday...then weaken
into next weekend as a trough of low pressure develops near the
West Coast.

The cooling that began Saturday as a result of weakening high
pressure aloft and a coastal eddy will continue for most areas
today with the greatest cooling in the valleys.

Satellite imagery and lightning detection data shows a large
convective complex over northwest Mexico. The GFS initializes this
reasonably well and takes the bulk of the mid and high level
moisture westward across northern Baja through tonight...possibly
just grazing far southern California. The vertical distribution of
this moisture is less than optimal for convective development in
Southern California with most of it 600 mb and above and the bulk
of it from 500 to 300 mb.

An influx of monsoonal moisture for late in the week could be
more favorably distributed for afternoon convection over the
mountains...extending down to around 700 mb. With the developing
trough of low pressure near the West Coast for next weekend...
drier southwest flow aloft should not be too far away to the
northwest.

&&

.AVIATION...
241500Z...Coast...Low clouds with bases at around 400-900 feet msl
and local vis 3-5sm will scatter out by 17Z. Scattered low clouds
may linger along the immediate coast today. Coastal clouds will
appear between 04-08Z tonight with bases 800-1200 feet msl and
spread a little farther inland. Scatter out Monday around 16-17Z.
Otherwise, scattered to broken high clouds today and tonight, mixed
with diffused smoke.

&&

.MARINE...
No hazardous marine weather is expected through Thursday.

&&

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

&&

.SGX Watches/Warnings/Advisories...
CA...Heat Advisory until 8 PM PDT this evening for Apple and Lucerne
     Valleys-Coachella Valley-Riverside County Mountains-San
     Bernardino County Mountains-San Bernardino and Riverside
     County Valleys-The Inland Empire-San Diego County Deserts-
     San Diego County Mountains-San Diego County Valleys-San
     Gorgonio Pass Near Banning.

PZ...None.
&&

$$

PUBLIC...JAD/17
AVIATION/MARINE...MM



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