Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 201649
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
949 AM PDT Tue Jun 20 2017

.SYNOPSIS...
Blazing heat will affect the deserts with the heat peaking this
afternoon through Wednesday. A shallow marine layer will continue
to moderate conditions along the coast with areas of nocturnal
clouds and fog...lingering into the afternoons at some beaches. It
will be a little cooler to end the week as onshore flow
increases, extending the marine influence farther inland. Inland
areas will remain hot this week. Summer officially begins at
9:24 this evening.

&&

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

Massive ridge is parked over the Desert Southwest, centered over
Arizona. Heights continue to increase as do low level temperature
fields. This is setting the stage for the peak of this heat event
across inland locales today and tomorrow. The H85 temp off the
San Diego sounding this morning was 28.4C. GFS shows it reaching
and peaking near 30.5C tomorrow. Record for June at San Diego is
31C.

So the heat is on, except near the coast with a continued shallow
marine layer influence. The San Diego sounding this morning showed
an exceptional inversion just some 500 FT off the surface with
strength at near +14C! The biggest forecast challenge is for
areas just inland from the coast, inland Orange County and the
San Diego inland Valleys, in just how hot it could get. I do like
that we are on the higher end of guidance for these locales, so no
changes will be made to forecast Max Ts this morning.

The Coachella Valley and the San Diego County deserts will see
their peak heat today and Wednesday with forecast highs into the
lower 120s!

Thousand Palms had an incredibly hot low temperature this morning
of 96F degrees.

The record high at Palm Springs today is 122 (set last year) and
is 118F on Wednesday (set in 1968). These records are in
jeopardy. The all time record high for Palm Springs is 123F set
July 28th and 29th in 1995. While not forecast, this is possible.

Global models continue to show the ridge strength lessening a tad
Thu, and then actually re-strengthening a bit Fri-Sat. This looks
to keep the heat wave for longer duration for the deserts and
will assess possible expansion in time of the heat headlines
later today.

A weak perturbation at upper levels (above H50) moves around the
ridge periphery this weekend (moving in from the S-SW). Moisture
increases aloft with this wave, but no rain is forecast at this
time.

&&

.AVIATION...
201530Z...Coast...Stratus, with bases 300-700 ft MSL and tops to
1000 ft MSL, will slowly clear towards the coast over the next few
hours. VIS of 1/2-3SM FG/BR will improve to P6SM by late morning, as
well. Portions of the beaches may remain cloudy throughout the day
due to a 14 deg C marine layer inversion. Low clouds will redevelop
this evening, with similar tops, bases and lowered VIS.

Valleys/Mountains/Deserts...P6SM vis and SKC through Wednesday
morning. High density altitude at KPSP and KTRM with max
temperatures 118-122 deg F.

&&

.MARINE...
Areas of dense fog, with visibility of 1 nm or less, is possible
through Thursday during the nights and mornings due to a shallow
marine layer. Otherwise, no hazardous marine weather is anticipated
through Saturday.

&&

.BEACHES...
A southerly swell of 3-4 ft/13 sec from 165-170 degrees, in addition
to short-period westerly swells and large tidal swings (high tides
of 6.5-7 ft with low tides around -1.0 ft), will result in strong
and dangerous rip and longshore currents through Thursday. This
swell will also likely create surf to 5 ft at Orange county beaches
and San Diego county beaches north of Oceanside. A Beach Hazards
Statement remains in effect through 10 PM Thursday. This Statement
may need to be extended beyond Thursday for possible minor tidal
overflow due to the aforementioned high tides which peak Friday
evening at around 7.3 feet (when the residual between predicted and
observed tides is factored in).

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 9 PM PDT Thursday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

     Heat Advisory until 9 PM PDT Wednesday for Orange County Inland
     Areas-Riverside County Mountains-San Bernardino County
     Mountains-San Bernardino and Riverside County Valleys-The
     Inland Empire-San Diego County Mountains-San Diego County
     Valleys-Santa Ana Mountains and Foothills.

PZ...NONE.
&&

$$

PUBLIC...Gregoria
AVIATION/MARINE...JJT


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