Area Forecast Discussion
Issued by NWS San Diego, CA

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468
FXUS66 KSGX 221652
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
945 AM PDT Mon May 22 2017

.SYNOPSIS...
Continued hot in the Inland Empire and the Lower Deserts through
Tuesday with high pressure aloft. Cooler near the coast with night
and morning low clouds and dense fog. Cooling will spread farther
inland Wednesday as the high weakens. Further cooling Thursday and
Friday with a trough of low pressure moving inland. This trough may
produce areas of light rain or drizzle west of the mountains Friday
morning. Dry and warm over the weekend with weak high pressure aloft.

&&

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

A weak shortwave trough passed overhead last night and deepened the
marine layer just enough so that low clouds/dense fog extended 10
miles inland. The marine layer was 800-1000 feet deep this morning
with a strong 10C inversion just above.

Satellite image showed an expansive area of low clouds over the
coastal waters stretching from the CA/OR border southward to central
Baja. The low clouds cleared back to the coast fairly quickly this
morning, but may linger at a few of the beaches through early
afternoon.

Weak ridging aloft takes place tonight with 5H rises of 20 dm
tonight. This should suppress the marine layer slightly, and if that
happens the low clouds/dense fog would not extend quite as far
inland Tuesday morning.

Coastal and western Valley temperatures at 9 AM were running a few
degrees cooler than 24 hours ago, while the lower deserts were 2-4
degrees higher where it will be another unseasonably hot day with
highs from 107-110. Tuesday will just as hot too, but record highs
appear a little out of reach. The record at Palm Springs today is
113, and is 114 Tuesday. This early season heat will elevate the
heat risk in the lower deserts.

The upper ridge weakens Wednesday and a slowly deepening marine
layer will send low clouds a little farther into the valleys
Wednesday morning. The valley highs Wednesday will be about 10
degrees lower, while the lower deserts will be about 5 degrees
lower.

*From previous forecast*

.LONG TERM (Thursday through Sunday)...
A trough of low pressure over the western states will bring
stronger onshore flow for Thursday and Friday. Periods of strong
gusty winds are expected for the mountains and deserts and could
be near advisory strength at times. Greater cooling will spread
inland with high temperatures for inland areas around 10 degrees
below average on Friday. The marine layer will deepen enough for
coastal low cloud and fog to extend into the inland valleys for
late Wednesday night into Thursday morning with continued
deepening taking it onto the coastal mountain slopes Thursday
night into Friday morning. The lower resolution global models
along with the 6-km local workstation WRF with GFS boundary
conditions all show light precipitation from the coast waters
inland to the coastal mountain slopes for late Thursday night into
Friday morning. A slight chance of showers has been added to the
forecast for this time period...but any rainfall is expected to be
light.

For next weekend...high pressure aloft will return along the West
Coast bringing a warming trend for inland areas with high
temperatures warming to a few degrees above average by Memorial
Day. Areas of night and morning low clouds and the marine layer
will keep high temperatures near the coast near average.

&&

.AVIATION...
221633Z...Coast/Valleys...Through 23/0200 UTC, mostly SKC and P6SM
vis, except at/near the beaches where BKN-SCT clouds 1000-1500 ft
msl may linger. Marine layer inversion strength of 10 deg C. 23/0200-
1600 UTC, low stratus/dense fog likely re-developing about 10-15 sm
inland with bases 300-600 ft msl and tops 700-1000 ft msl, with
areas of vis 1/4-2 sm. Confidence in cig heights and vis for KSAN,
KCRQ and KSNA TAFs is moderate with moderate confidence in timing
and high confidence in low stratus/fog occurrence.

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

&&

.MARINE...
A shallower marine layer will likely bring dense fog to the coastal
waters tonight into Tuesday morning, producing visibilities of 1 NM
or less.

Also, 20 kt northwest wind gusts will be possible over the outer
waters near San Clemente island each late afternoon and early
evening through Friday.


&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...Moede
AVIATION/MARINE...Harrison



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