Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 202143
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
243 PM PDT Tue Jun 20 2017

...Heat Wave Continues Inland with Excessively Hot Conditions Over
the Deserts...

.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 (598DM) is parked over the Desert Southwest,
centered over Arizona. Heights continue to increase locally as do
low level temperature fields. This is setting the stage for the
peak of this heat event across inland locales this afternoon 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! Given this, some locales across inland
Orange County and the San Diego inland Valleys could soar into the
mid-upper 90s. Have stayed at or above guidance for these
locales.

The Coachella Valley and the San Diego County deserts will see
their peak heat this afternoon and Wednesday with forecast highs
into the lower 120s! Palm Springs is currently at 122F, which ties
the record high for the date, previously set last year! The all
time record high for Palm Springs is 123F set July 28th and 29th
in 1995. There is the potential for this to be tied or broken
today and/or tomorrow.

Thousand Palms had an incredibly hot low temperature this morning
of 96F degrees (wind stayed up so it remained mixed). Lows
tonight in mixed locales (generally along and east of I-10) are
forecast to only fall into the mid-upper 90s. Yes, that is the
LOW temp! Am forecasting a low at Thousand Palms of 98F degrees
tonight.

Global models continue to show the ridge strength lessening a tad
Thursday, and then actually re-strengthening a bit Fri and into
the weekend. This will keep the heat wave for longer duration for
the deserts. Granted, temps will lower a few degrees through the
end of the week, but will remain excessive. For this reason, have
extended in time the Excessive Heat Warning for the lower deserts
(Coachella Valley and the San Diego County deserts) through Sunday.
The Excessive Heat Warning for the High Deserts was extended in
time through Friday. The heat by Sunday may become borderline for
a warning for the lower deserts, but it was decided to go all the
way through the weekend given the fact that this is an excessive
heat wave event and the long duration can have cumulative effects
on the body.

For the hot areas of the Inland Empire, mountains and inland
valley region, the heat will continue through Wednesday, but then
it will tame somewhat for the latter part of the week with slightly
lower temps above the surface (H85) and a better marine influence
further inland. Still though continuing above average.

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, so will have to monitor to see if
perhaps an isolated shower or even thunderstorm may occur, but at
this point the chance is really too low to place in the forecast.
We think right now there is a high likelihood of it remaining dry
across our service area through the weekend. This upper level wave
will likely bring in some mid-high level cloudiness for a brief
time late Sat-Sun.

&&

.AVIATION...
202100...Coast...Stratus, with bases around 700 ft MSL and tops to
1100 ft MSL, will linger along portions of the beaches throughout
the day due to a strong marine layer inversion. Low clouds will
redevelop along the coast and around 10 miles inland this evening,
with similar tops and bases. VIS of 1/2 SM FG is expected for some
beach areas and over coastal mesas by Wednesday morning. Similar
limited clearing along the beaches is possible again Wednesday
afternoon.

Valleys/Mountains/Deserts...P6SM vis and SKC through Wednesday
afternoon. 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 Friday during the nights and mornings due to a shallow
marine layer. A Marine Weather Statement is in effect through the
period. 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 has been extended through 10 PM Friday to account for
minor coastal flooding from the large evening high tides.

&&

.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 Sunday for 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.

     Excessive Heat Warning until 11 PM PDT Friday for Apple and
     Lucerne Valleys.

PZ...NONE.
&&

$$

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



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