Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 221712
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1012 AM PDT Thu Jun 22 2017

...Excessive heat to continue through Monday in the lower deserts
including the Coachella Valley...

.SYNOPSIS...
It will continue excessively hot in the deserts through Monday
under high pressure aloft. It will not be quite as hot in the
valleys the next couple of days as onshore winds increase,
extending the marine influence farther inland. The marine layer
will continue to moderate temperatures in the coastal region with
clouds lingering into the afternoons at some of the beaches. The
mountains will remain hot through the weekend.

&&

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

...Update - Deserts Continue to Bake, While Temps Moderate
Slightly West of the Mountains...

The morning San Diego sounding showed subtle cooling at lower
levels with the H85 temp at 27.8C, down from 28.6C 24 hour ago.
This is indicative of the massive ridge, parked over Arizona,
easing its strength over Southern California, though only by a
tad.

There was a moisture surge into the lower deserts yesterday and
again today, even higher. Current dewpoints are into the 60s
across the Coachella Valley with even some lower 70F dewpoint
readings in the far southern valley and the San Diego County
deserts! So temps will take a slow rise to 100 but after mixing in
the afternoon, we still anticipate highs to get up into the 110s.
For the high deserts 105-110 with continued very low dewpoints in
the 30s.

For the mountains on west, temps will be cooler due to a larger
onshore pressure gradient, allowing for a deeper marine layer and
more modified pacific air further inland. The depth of the marine
layer has increased since yesterday, so beaches may stay overcast.
Highs will only stay in the 60s there.

Winds peaked to 33 mph across the San Bernardino desert slopes
into the high desert (through and downwind of the Cajon Pass).
Similar winds are expected there late this afternoon and early
this evening with a few hours of gusts to around 35 mph and with
the low relative humidity (5-15%) will create just a few hours of
conditions favorable for quick spreading wildfires. However, a Red
Flag Warning will not be issued as it looks borderline and of
short duration.

No significant changes were made to the forecast this morning. See
previous discussion below for further forecast details. /Gregoria

...Previous Discussion (Issued at 352 AM PDT Thu Jun 22 2017)...

Excessively hot conditions will continue across the deserts
through Monday as a high pressure ridge remains entrenched across
the SW region. The build up over many days means a continued
threat to public safety even as the temperatures have fallen a few
degrees below the hottest temperatures of a couple days ago.

Although temperatures will not be quite as hot as what we saw a
few days ago, a minor flare up in the temperatures will occur
Sunday as the high becomes a tad stronger and temperatures may
flirt with the 120 mark once again in the lower deserts. The
excessive heat warnings have been extended for the lower deserts
through Monday as temperatures will reach excessive levels once
again.

A strong and shallow marine layer will continue cloudy and foggy
conditions near the coast and into the western valleys each night
and morning. As the high strengthens this weekend the marine
intrusion will probably focus back right along the coastal strip.
Then after Monday should deepen again and bring more extensive
cooling into the valleys.

The ridge breaks down after Monday as the high slowly flattens
out and by mid next week a Pacific trough slowly builds into the
west coast...bringing an increase in cooling temps aloft to all of
the region and finally inland temperatures should settle back a
little closer to near normal levels.

&&

.AVIATION...
221629...Coast/Valleys...Stratus 15-25 sm inland, with bases 500-700
ft msl, tops 1600-2000 ft msl, and areas of vis 2-5 sm, will clear
to the coast through 1900 UTC. 1900-23/0000 UTC, mostly P6SM vis and
SKC, except at and near the beaches where BKN-OVC stratus clouds
around 1000-2000 ft msl and 5 sm vis may linger. 23/0000-1600 UTC,
low stratus re-developing 15-25 sm inland, with bases around 400-800
ft msl, tops around 1500-2000 ft msl, areas of vis 1-5 sm and local
vis down to 1/4 sm.

Mountains/Deserts...P6SM vis and mostly SKC through Friday morning.

&&

.MARINE...
A shallow marine layer will continue to bring patchy dense fog (with
visibilities of 1 NM or less) to the coastal waters this morning.
Patchy dense fog will be possible during the nights and mornings
through the weekend. Otherwise, no hazardous marine weather is
expected through Monday.

&&

.BEACHES...
A south swell of 3-4 ft at 13-15 seconds from 165-170 degrees
combined with a short-period west swell 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 Friday. This
swell will also produce surf to 3-6 ft (with local sets to 7 ft) at
Orange county beaches and San Diego county beaches north of
Oceanside. Also, the high tides will likely reach around 7+ ft
during the evenings today through Saturday. Tides this high may
result in minor tidal overflow at low lying beaches. A Beach Hazards
Statement continues through Friday.


&&

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

     Excessive Heat Warning until 9 PM PDT Sunday for Apple and
     Lucerne Valleys.

PZ...NONE.
&&

$$

PUBLIC...Gregoria (Update)/Brotherton (Prev Discussion)
AVIATION/MARINE...Harrison



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