Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 242020
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
120 PM PDT Sat Jun 24 2017

.SYNOPSIS...
High pressure aloft will continue the hot weather far inland this
weekend, while a marine layer and onshore flow keep coastal and
western valley areas mild, with periods of nocturnal low clouds and
fog. High pressure aloft will weaken and move to the south next week
as a pair of low pressure systems move inland to the north through
Wednesday. This will deepen the marine layer and drop high
temperatures to average or below for late June. Strong rip currents
and higher than normal tides will prevail into this evening.

&&

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

Satellite imagery this afternoon showed marine stratus continued
offshore and at some beaches, but clearing was more complete than
earlier thought. Over the mts, towering cumulus clouds had developed
over portions of the Riverside and San Bernardino County Mts.....
Surface pressure gradients to our local deserts were 5-9 MBS
onshore. Peak wind gust reports around midday have been in the 25-35
MPH range near the passes, otherwise well below 25 MPH.

Based on the cumulus development, it appears there is a small chance
for a lightning strike or two over the San Bernardino Mts before
sunset. The RAP13 shows isolated, elevated cape values in the mid-
levels at around 120 J/K over the San Bernardino Mts through 01Z,
but winds and moisture to support even scattered development appear
lacking. At this time...POPs are below 10%, however there is a
chance for a dry lightning strike or two before sunset along the
higher terrain.

The high pressure ridge over the SW will maintain through Sunday,
then weaken and slip westward to reemerge stronger again over the
EastPac along 145W. At the same time, a cut-off low off the CA Coast
near 135 W, will weaken and ride the top of the ridge inland toward
the PacNW. Another weak shortwave will follow from the NW and
reinforce the troughing over the West through midweek. These events
will suppress heights/thickness over SoCal and much of the SW, and
increase the onshore flow and the marine layer depth, resulting in
cooler weather.

In the meantime, several models and MET/ECMWF MOS guidance indicate
a thinning of the marine layer through Mon as a stronger low-level
NW flow develops over the CA Bight. Other factors such as falling
heights, a weak shortwave trough moving overhead, and sfc-pressure
falls over the Great Basin suggest maintaining the marine layer
depth. Perhaps that will occur, but clouds may be still be more
limited. In any case, that is about our only forecast issue for the
next several days.

For the latter half of next week there is little height/thickness
recovery over the SW, but onshore flow weakens a bit so the marine
layer may decrease again, resulting in modest temp gains again into
next weekend.

&&

.AVIATION...
241955Z...Coast/Valleys...Through 25/0000 UTC, primarily P6SM vis
and FEW-SCT clouds AOA 15000 ft msl, except at and near the beaches
where BKN clouds 1000-2000 ft msl are likely to linger. 25/0000-1500
UTC, stratus re-developing and moving inland 10-15 sm, with bases
around 300-700 ft msl, tops around 1200-1700 ft msl, areas of vis 2-
5 sm, and local vis down to around 1/4-1/2 sm along higher coastal
terrain/inland mesas. Confidence in cig heights/vis is low.

Mountains/Deserts...BKN-SCT cumulus clouds with bases around 10000
ft msl over the mountains will continue through 25/0000 UTC, with
just the slightest risk of a lightning strike or two. These clouds
dissipating after 25/0000 UTC. Otherwise, FEW-SCT AOA 15000 ft msl
and P6SM vis continuing through Sunday morning.

&&

.MARINE...
Northwest wind gusts over the outer waters may reach 20-25 kt during
the afternoons and evenings Sunday through Tuesday, potentially
resulting in conditions hazardous to small craft.

&&

.BEACHES...
High tides will reach 7+ ft again this evening. Tides this high may
result in minor tidal overflow at low lying beaches. The Beach
Hazards Statement continues through 11 PM this evening. High tide
will fall below 7 feet Sunday, lowering the tidal overflow threat.


&&

.FIRE WEATHER...
Heat and gusty winds along the ridges, desert slopes and passes will
create a heightened risk of wild fire spread late today into the
evening and again on Sunday. There is also a small chance for
isolated dry lightning strikes in the San Bernardino Mts into early
evening. Drier air aloft will preclude any threat of convection over
the mts on Sunday.

&&

.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.

     Heat Advisory from 10 AM to 9 PM PDT Sunday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains-Santa Ana Mountains and Foothills.

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

     Beach Hazards Statement through this evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

$$

PUBLIC...JAD
AVIATION/MARINE/BEACHES...Harrison



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