Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 301615
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
915 AM PDT Thu Mar 30 2017

...Severe potentially damaging winds this afternoon and evening over
the mountains and deserts...

.SYNOPSIS...
A deep low pressure trough moving across the Great Basin today will
bring strong west winds to the mountains and deserts this afternoon
and evening. Cooler Friday behind the trough with winds shifting to
the northeast. High pressure rebuilding over the region Saturday
will bring sunny and warm weather this weekend. Cooler early next
week as another trough moves in from the northwest.

&&

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

Current forecast is on track today and all models are showing a
strong wind event in the mountains and deserts. Winds were starting
to increase in the high deserts this morning. At 9 AM, Palmdale
reported northwest winds of 32 mph with gusts of 39 mph, and Daggett
had southwest winds of 29 mph with gusts to 36 mph.

A deep trough over central CA will intensify and move southeast
across the California interior through this evening. This deep
trough is unusually strong with 850 mb winds of 50-55 kts between 18-
06Z. Winds this strong occur about once every 10 years, and are 3-4
standard anomalies above normal. Desert winds of 30-40 mph will gust
to 60 mph or more. Strong wind gusts in mountain waves down the
eastern slopes of the mountains will surface in parts of the
Coachella Valley and the San Diego County Deserts. Strong cross
winds and reduced vis in blowing dust and sand will create hazardous
travel conditions. A High Wind Warning is in effect from Noon to 11
pm today.

On the other end of the weather spectrum, low clouds and dense fog
have moved into southwestern San Diego County due to a coastal eddy
over the coastal waters. Vis was down to 1/4 mile at Imperial Beach
and 1/2 mile at North Island at 9 AM.

Winds and weather in the rest of the coastal and valley zones will
quieter west of the mountains with mostly sunny skies, above average
temperatures and breezy west winds of 10-20 mph in the afternoon.

*From Previous Discussion*

As the low shifts to the east winds will shift to the north late
tonight and into Friday morning. There may be another period of
strong winds through Friday morning, although not nearly as severe
as what we are expecting with the WNW. Northerly winds will continue
through Friday night although not nearly as strong but a wind
advisory may be necessary to cover this period after the threat for
high winds has ended.

Ridging and moderating temperatures and lighter winds will build
in for Saturday and Sunday. An inside slider trough will bring
another cooldown Monday and Tuesday as well as another threat for
strong winds. Another ridge will build in for Wednesday and
Thursday for another period of moderating temperatures.

Mid latitude moisture transport and Pacific Jet will bring the
potential for widespread precipitation to Norcal by the end of
next week although it is looking like this system will not make it
down to Southern California. Will keep an eye on this though for
late season precip potential.

&&

.AVIATION...
301600Z...Patchy fog near the coast this morning could impact KSAN
with CIGS 300-500 ft MSL and VIS 1Sm or less until about 17:30Z, but
not likely to impact other coastal TAF sites. Otherwise, mostly
clear skies today. Coastal low clouds to return and spread rapidly
inland this evening after 00Z, mostly in San Diego County. Bases
will be rising to between 1000-2000 feet msl. Low clouds could
spread inland to the coastal slopes by 06Z, before northeast to east
winds develop and begin to clear out the low clouds.

Mountains and deserts...areas of winds 25-35 KT with gusts 40-50 KT
after 20Z near mountain crests, desert mountain slopes and some
lower elevation desert locations. Strong and variable winds could
occur at KPSP and KTRM, with peak winds likely between 23-04Z this
afternoon/eve. LLWS and strong up/downdrafts will occur over and
east of the mtns, with isolated vis reductions in blowing dust/sand
in the deserts. Winds will diminish after 06Z.

&&

.MARINE...
Strong west and northwest winds will develop this afternoon and
continue into early Friday, particularly in the outer coastal
waters. A small craft advisory contains the details on winds and
seas. In portions of the outer waters, winds will gust over 30 knots
at times and combined seas could exceed 10 feet. Winds and seas will
diminish Friday morning. No hazardous marine weather is expected
through Sunday, but strong winds could return Monday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning from noon today to 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.

PZ...Small Craft Advisory from 1 PM this afternoon to 8 AM PDT Friday
     for Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

&&

$$

PUBLIC...Moede
AVIATION/MARINE...PG


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