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Forecast Discussion for San Diego, CA

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000
FXUS66 KSGX 212136
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
236 PM PDT Tue May 21 2019

.SYNOPSIS...
A cold low pressure trough will bring more unseasonably cool, wet
and windy weather Wednesday with mountain snow above 5,500 feet.
A Winter Weather Advisory is in effect for the San Bernardino and
Riverside County Mountains. Scattered showers will continue into
Thursday, followed by mainly dry weather Friday and Saturday
except for some scattered mountain showers. Another trough on
Sunday will bring more showers and gusty winds that may linger
into Memorial Day.


&&

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

Scattered light showers through early this afternoon were
confined to the mountain foothills and San Diego County valleys.
Amounts were light and ranged from 0.01 to 0.05" in most areas.
The highest total was at Yucaipa Ridge in the San Bernardino
County mountains with 0.12". Scattered light showers will continue
in these areas through tonight. It was a windy day in the
mountains and deserts with gusts to 52 mph at the Mt Laguna
Observatory, 53 mph at Julian, and 55 mph at Boulevard. Strong
winds and blowing sand caused the closure of Indian Canyon Road in
the northern end of the Coachella Valley this afternoon. Thousand
Palms had a wind gust to 40 mph, and the Barstow-Daggett Airport
gusted to 63 mph at 11 AM. A Wind Advisory is in effect for these
areas until 11 PM tonight.

Wednesday will feel more like January than May as a potent and
unseasonably strong upper low over Oregon tonight digs south and
treks across Southern California. Strong dynamics coupled with
cold air aloft under a warm May sun will destabilize the
atmosphere for potential thunderstorms too. 500 mb temperatures
over the SBD Mtns fall from -11C at 12Z to -22C at 18Z, and the
strong CAA will drop the snow levels to 5,500 feet. Convective
snow bursts will reduce vis at times. A Winter Weather Advisory
will be in effect from 9 AM to Midnight Wednesday for the San
Bernardino and Riverside County Mountains above 5,500 feet.
Palomar Mountain and Mount Laguna may also see an inch or two of
snow.

The trough axis passes through on Wednesday evening and becomes a
closed upper low over the Lower Colorado River Valley Wednesday
night. Residual moisture and instability will keep scattered showers
going through Thursday, but they will gradually taper off during
the afternoon and evening as drier air fills in from the north.

The weather from Thursday night through Saturday will be mostly
dry. Then on Sunday and Monday another deep low will move across
northern Baja for more showers, high elevation snow and below
average temperatures. Depending on the ultimate speed of this
trough, showers may linger into Memorial Day. Regardless, Memorial
Day will be unseasonably cool day with high temperatures from
10-20 degrees below average in the valleys, mountains and deserts.

Outlook for next week: The GEFS ensemble projects the overall
trough pattern to prevail over the West for continued cooler-than-
average weather.

&&

.AVIATION...
212000Z...Coast/Valleys...SCT-BKN stratus with bases 2500-4000 ft
MSL will continue through tonight, with tops increasing to 7000 FT
this evening. Cig coverage will be greatest over SD County with high
confidence in KSAN/KCRQ seeing prevailing BKN-OVC skies through
tomorrow AM. -SHRA at times, mainly after 21Z and most likely for
inland San Diego County, persisting into tomorrow. Frequent vis
restrictions not anticipated at TAF sites, however brief reductions
during isolated -SHRA are possible.

Mountains...Prevailing OVC with isolated -SHRA after 21/21Z and vis
2-4 in BR on obscured slopes. W SFC winds gusting 30-40 kts through
21Z, strengthening this evening with gusts 35-50 kts, strongest on
desert-facing slopes. SFC winds will weaken by 22/09Z. STG-SVR UDDFS
and LLWS are likely over and east of the mtns, especially this
PM/evening.

Deserts...Strong SFC winds this evening at KPSP/KTRM, prevailing NW.
Potential for rotors in VCNTY of KPSP this afternoon with periods of
NE SFC winds, LLWS and STG-SVR UDDFTS. Expect frequent SFC gusts 25-
30 kts. Moderate confidence in periods of stronger gusts between 20-
00Z, and again after 05Z Wed, with gusts 35-40 kts possible. AWW in
effect for KPSP through 09Z Wed. Vis may be reduced to 2 SM or less
in BLDU.

&&

.MARINE...
A Small Craft Advisory is in effect through 5 PM today, followed by
a Gale Warning 5 PM today through 5 PM Wednesday. WNW winds gusting
to 25 kts and combined seas of 7-10 ft through this afternoon. Winds
will strengthen in the evening into the overnight hours, with gusts
to 35 kts over the Outer Waters, and 25-30 kts over the Inner
Waters. Combined seas will increase substantially, with 10-12 ft
seas in the Inner Waters, and 12-17 ft in the Outer Waters, highest
NE of San Clemente Island.

Isolated showers will be possible at times through Thursday,
although thunderstorms are not expected at this time.

&&

.BEACHES...
Building west northwest swell with 12 second period may generate
locally elevated surf conditions on the beaches Wednesday. A Beach
Hazards Statement is in effect from midnight tonight to 3 AM
Thursday.

&&

.SKYWARN...
Skywarn activation may be requested Wednesday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 9 AM Wednesday to midnight PDT
     Wednesday night for Riverside County Mountains-San
     Bernardino County Mountains.

     Wind Advisory until 11 PM PDT this evening for Apple and Lucerne
     Valleys-Coachella Valley-Riverside County Mountains-San
     Bernardino County Mountains-San Diego County Deserts-San
     Diego County Mountains-San Gorgonio Pass Near Banning.

     Beach Hazards Statement from midnight PDT tonight through late
     Wednesday night for Orange County Coastal Areas-San Diego
     County Coastal Areas.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm-Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

     Gale Warning from 5 PM this afternoon to 5 PM PDT Wednesday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm-Waters from San Mateo point to the Mexican
     Border Extending 30 to 60 nm out including San Clemente
     Island.

&&

$$

PUBLIC...Moede
AVIATION/MARINE/BEACHES...Rodriguez

Previous Forecast Discussions may be found at
NWS San Diego, CA (SGX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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