Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 171657
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PDT Sat Jun 17 2017

.SYNOPSIS...
Very hot weather will prevail over the deserts under strong high
pressure aloft through at least next Thursday, with Tuesday and
Wednesday likely the hottest days when a few locations could exceed
120 degrees. Mild weather will occur along the coast with low clouds
and fog at times, locally dense. The inland valleys will hot at
times, with peak heat there Tuesday and Wednesday as well. Slight
cooling will occur early next week.

&&

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

Marine layer was a little deeper this morning, with cloud tops as
high as around 1500 feet. Locally dense fog occurred on the San
Diego County mesas and over nearby higher terrain this morning.
Except for the area from La Jolla to Point Loma, all coastal areas
cleared by mid-morning. High temps today should be similar to those
on Friday except slightly cooler in some of the western parts of the
valleys due to the slight deepening of the marine layer.

A 592 DM high was centered over the Central Coast of California with
ridging southeast through NW Mexico. The axis of the high will
gradually shift east to Nevada-Arizona-Chihuahua through Sunday and
then strengthen through Tuesday over Arizona where it could reach
598 DM. Over our area, there will be variations of the theme, with
very hot weather with very low humidities in the desert but a marine
layer, which rarely dissipates entirely in June, along the coast,
and a strong temperature gradient from the mild coast through the
very warm/hot valleys to the extreme heat in the desert. The all-
time high at Palm Springs is 123, but right now I am thinking they
will fall a couple degrees short of that as models show 850 MB temps
in the 31-33 deg C range near the Coachella Valley, which is not
quite as hot as the 34-36 deg C range farther east and northeast
where 850 MB temps will be within about 1 deg C of records based on
the SPC sounding climatology page. Current forecast of 121 for PSP
Tue/Wed looks good and will not change that.

Closer to the coast, the location of the sharp temperature gradient
between the coast and valleys will depend on the marine layer depth,
which should get gradually more shallow Sunday through Tuesday. Some
temps over 105 could occur in the Inland Empire at times, over 100
in the far inland parts of the San Diego County Valleys and temps
could approach 100 over far inland Orange County, mainly
Tuesday/Wednesday. Some dense fog will occur near the coast, and
possibly could be along the immediate coast Tue/Wed, if it does not
dissipate entirely. There is hint of cooling as the upper high
weakens slightly, then low-level flow, including at 850 MB, becomes
solidly westerly and strengthens Friday/Saturday for more
substantial cooling as a trough moves south over the Northwest, as
the upper high shifts southeast, though ECMWF is has that troughing
moving east versus south, so it would have less of a cooling trend.
Most likely, temperatures late next week will lower to "just" those
of this weekend, still above the hot averages that the desert has
for late June.

&&

.AVIATION...
171600Z...Low clouds which affected the coast and inland valleys
have quickly dissipated. Clear skies with unrestricted visibility
will prevail through this evening. However, low clouds and fog could
re-develop again along the coast tonight (moderate confidence),
potentially affecting KSAN, KCRQ, and KSNA with CIGS near 600-800 FT
MSL and 3-5SM visibility, perhaps down to 1/2-1SM briefly. Onset
timing of potential IFR looks to be 04-06Z for KSAN and KCRQ and
after 09Z for KSNA. The low clouds and fog will quickly dissipate
again by around 15Z Sunday.

&&

.MARINE...
Areas of fog with local visibilities 1 NM or less is forecast,
mainly during the late nights and mornings into early next week.
Otherwise, no hazardous marine weather is anticipated through
Wednesday.


&&

.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 Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near
     Banning.

     Heat Advisory from 11 AM this morning to 9 PM PDT Wednesday for
     Riverside County Mountains-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Mountains.

     Excessive Heat Warning from 11 AM this morning to 9 PM PDT
     Thursday for Apple and Lucerne Valleys.

     Heat Advisory from 11 AM Monday to 9 PM PDT Wednesday for Orange
     County Inland Areas-San Diego County Valleys-Santa Ana
     Mountains and Foothills.

PZ...NONE.

&&

$$

PUBLIC...Maxwell
AVIATION/MARINE...Gregoria



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