Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 231533
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
833 AM PDT Sun Apr 23 2017

.SYNOPSIS...
Increasing onshore flow through Monday will bring cooling well
inland, more nocturnal low clouds and fog as the marine layer
builds, and strong westerly winds across the mountains and deserts.
Fair, dry, and a little warmer midweek as the marine layer shrinks
and onshore flow weakens. Then, windy and cooler again Thursday and
Friday as a strong low pressure center develops over the Great
Basin. Fair, with a warming trend next weekend as the wind lets
up and high pressure rebuilds aloft.

&&

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

Patchy low clouds were evident over the coastal waters in satellite
imagery this morning, otherwise high clouds were the main feature,
and particularly thick over the Coachella Valley. The 12Z miramar
sounding had a sfc-based inversion, topping out near 2500 FT.
Cooling of from 2 to 5 degrees C was noted below 2500 FT. At 8 AM
PDT...Surface pressure gradioents were 4-5 MBS onshore KSAN to the
deserts. Winds were noticeably stronger across remote mtn areas,
with peak wind gusts SW at 30 to 35 MPH.

Based on the 12Z sounding this morning, and increasing onshore sfc
pressure gradients, it should be cooler today. Forecast updates were
issued earlier to account for less low clouds west of the mountains,
and more high clouds over much of the CWA, especially the Coachella
Valley.

From previous discussion...

.SHORT TERM (Today through Tuesday)...
A trough of low pressure will move through California today with a
second trough of low pressure moving inland on Monday. This will
bring stronger onshore flow with gusty west winds in the mountains
and deserts for late afternoon through late at night. Winds are
expected to strongest on Monday afternoon and night with gusts to
55 mph at times and isolated gusts to 65 mph.

The onshore flow will bring 10 to 15 degrees of cooling today for
coastal and valley areas with less cooling farther inland. The
cooling will continue for inland areas on Monday.

Satellite imagery shows a return of patchy stratus along the San
Diego County coast with the marine layer having deepened to around
1200 feet. Stratus coverage is expected to expand some past
sunrise and may extend northward into Orange County. Additional
deepening is expected to allow the stratus to push into portions
of the inland valleys for tonight into Monday morning.

Warming will resume on Tuesday as subtropical high pressure
develops off the West Coast. This will return high temperatures to
near average.

&&

.LONG TERM (Wednesday through Saturday)...
High pressure aloft will continue to strengthen over the eastern
Pacific bringing more warming for Wednesday and Thursday with high
temperatures warming to around 5 degrees above average. The marine
layer will become shallower with night and morning coastal low
clouds and fog becoming patchier.

A trough of low pressure moving southeastward through the Great
Basin on Thursday will bring stronger onshore flow across Southern
California for Thursday night and Friday with stronger and gusty
west winds in the mountains and deserts and cooling and with near
seasonal high temperatures on Friday.

A period of weaker offshore flow may follow for Friday night into
Saturday with strengthening high pressure aloft off the West Coast
bringing warming for next weekend.

&&

.AVIATION...
231530Z...Coast/Valleys...Patches of BKN clouds within 5-10 sm of
the coast, with bases 800-1400 ft msl and tops 1500 ft msl and local
vis 4-5 sm, should clear to the coast by 1800 UTC, with otherwise
P6SM vis and SCT-BKN clouds AOA 20000 ft msl. 1800-24/0000 UTC,
primarily P6SM vis and SCT-BKN clouds AOA 20000 ft msl. 24/0000-1500
UTC, BKN-OVC stratus re-developing and gradually filling the coast
and valley areas, with bases 1500-2000 ft msl and tops near 2500 ft
msl. Expect areas of vis 3-5 sm in the valleys.

Mountains/Deserts...West winds with sfc gusts 25-35 kt developing
along the ridges, desert slopes, through the San Gorgonio Pass, and
locally on the desert floor after 2100 UTC, with Mod-stg UDDFS and
pockets of LLWS possible over/east of the mountains.

&&

.MARINE...
Periods of northwest wind gusts of 25-30 kt and combined seas of 10-
12 ft are possible in the outer coastal waters Monday evening
through Friday evening. This would result in conditions hazardous to
small craft through much of the week in the outer waters.

Meanwhile for the inner waters, gusts of 20 kt and seas near 8 to 9
feet will be possible at times, but Small Craft Advisory conditions
are not anticipated.

&&

.BEACHES...
A southwest swell from 200 degrees at 3 ft/15 seconds combined with
elevated west swells will produce surf of 3-6 ft with occasional 7
ft sets today. The above normal surf will also create favorable
conditions for strong rip currents and longshore currents. A Beach
Hazards Statement remains in effect through 11 PM tonight.

A series of large short to moderate period northwest swells will
maintain elevated to occasionally high surf and strong rip
currents through most of the week.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through this evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

$$

PUBLIC...JAD/17
AVIATION/MARINE/BEACHES...Harrison



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