Area Forecast Discussion
Issued by NWS San Diego, CA

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730
FXUS66 KSGX 181616 AAA
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
915 AM PDT Wed Jul 18 2018

.MORNING UPDATE...
The only change this morning was to increase the pops a bit for late
this morning through the afternoon esp over San Diego County and in
the mountains where another easterly wave currently moving through
Imperial County will bring a little better chance for
showers/tstorms. Otherwise diurnal convection this afternoon/evening
focused over the mountains with fast easterly mid level flow being
the limiting factor in an otherwise juicy airmass (San Diego
sounding shows near 2" PWAT this morning). No other changes were
made to the forecast at this time.

&&

.SYNOPSIS...
Monsoonal moisture will continue the chance for mainly afternoon
and early evening showers and thunderstorms into Thursday...
mostly for the mountains...deserts...and inland valleys. Some of
those could move west of the mountains for this morning. A little
drier for Friday and Saturday. For Sunday through Tuesday...strong
high pressure will expand into Southern California with a warming
trend that will take high temperatures to 5 to 10 degrees above
average on Tuesday.

&&

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

Previous discussion issued early this morning.

A convective complex that was over west central Arizona around
midnight...has moved into the eastern deserts of Southern
California and continues to move towards the west. The HRRR
maintains this connection through around 10Z (3 AM)...after which
it shows a weakening trend as it moves towards the west southwest.
This could impact the Coachella Valley and the Riverside County
mountains...and portions of San Diego County early this
morning...especially the deserts...mountains...and inland valleys.
Strongest gusts with outflow from this complex have been around 50
mph. The HRRR also develops additional convection over portions of
San Bernardino...moving it towards the west southwest across the
San Bernardino County mountains and adjacent deserts...and
portions of the Inland Empire and Orange County early this
morning.

Beyond those short term trends...most of the changes to the
current forecast are relatively minor. The chance for mainly
afternoon and early evening showers and thunderstorms for the
mountains...deserts...and inland valleys. To the extent there is
some agreement among the models...the primary focus for showers
and thunderstorms for this afternoon and early evening is across
the mountains...high desert...and inland valleys with the
afternoon lower level convergence boundary towards the coastal
slopes of the mountains.

Some drying is expected for Friday and Saturday with not much
change in temperatures. This should reduce chances for afternoon
thunder near the mountains...but may not end it entirely. The
current forecast remains dry for this period with some afternoon
clouds for the mountains.

For Sunday through Tuesday...strong high pressure aloft centered
over Arizona is expected to move and expand towards the west
across Southern California with still some differences on the
placement and strength for the early to middle part of next week.
A warming trend is expected for this period with high temperatures
for Tuesday around 5 to 10 degrees above average. This will
elevate the heat risk for inland areas for Monday and Tuesday and
possibly longer.

&&

.AVIATION...
181520Z...Coast/Valleys...BKN-OVC low clouds within 10 miles of the
coast with bases 1000-1500 ft MSL and tops to 1800 ft MSL. Local vis
4 miles will occur in the valleys. Most areas will clear by 17Z,
except for local BKN stratus lingering at some immediate coastal
locations into the afternoon.

Isolated -SHRA/TSRA will be possible mainly in the valleys this
afternoon with strong up/downdrafts and local surface gusts over 30
knots possible. Stratus likely will be less extensive tonight, with
areas of low clouds within 5-15 miles of the coast with bases 0800-
1200 ft MSL and tops to 1500 ft MSL. Local vis 1-3 miles will occur
in the valleys through mid morning. The risk of low clouds clearing
at KSAN then redeveloping tonight is moderate-high so the confidence
in the TAF forecast is moderate-high.

Mountains/Deserts...SCT-BKN clouds based around 10000 feet MSL with
sprinkles early. After about 18/1900Z scattered SHRA/TSRA developing
over portions of the mountains and deserts through this evening.
Strong up/downdrafts and local gusts over 40 knots will be possible
along with reduced visibility in blowing dust across the deserts.
Brief heavy rain will be possible as well.

&&

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

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...17/JMB
AVIATION/MARINE...Small



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