Area Forecast Discussion
Issued by NWS San Diego, CA

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763
FXUS66 KSGX 212156
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
156 PM PST Tue Feb 21 2017

.SYNOPSIS...
Cooler and breezy Wednesday and Thursday with generally dry
northwest flow aloft. Strongest surface winds will be Wednesday
afternoon through Wednesday night along desert mountain slopes and
adjacent desert areas. Dry and a little warmer Friday and
Saturday. Precipitation looks to return to the area Sunday through
Tuesday as two upper- level troughs move across the area, with
gusty winds in the mountains and deserts at times.

&&

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

At 1 pm PST, water vapor satellite imagery displayed an upper-
level trough across central California, and an upper-level ridge
over central Baja. A few high-level showers moved across portions
of the San Bernardino County mountains and adjacent desert areas
today, and dropped mainly a few hundredths of an inch of
precipitation.

A weak upper-level trough will move across the region Wednesday
into Thursday. No precipitation is expected over the area from the
trough, however onshore flow will increase and create westerly
wind gusts of 45-55 mph over the mountains and into portions of
the deserts through the period. A Wind Advisory has been issued
for Wednesday afternoon through Wednesday night. Highs will lower
back to below normal Wednesday, and down 5-10 degrees below normal
by Thursday. Mostly zonal flow over the region Friday and Saturday
will maintain the cooler weather for the start of the weekend.

Models are in pretty good agreement with two upper-level lows
merging just off of northern California, and then two associated
troughs moving over southern California early Sunday through next
Tuesday. Precipitation is expected to be heaviest on Sunday and
Sunday night as a precipitable water plume of around 1.10 inches
moves across the area and upper-level dynamics are most favorable.
Snow levels look to be around 6000 ft Sunday, and lower to
possibly 4000 ft by Tuesday. Gusty southwesterly winds are
possible in the mountains as the first trough moves through, with
highs lowering 5-15 degrees below normal by Sunday. Additional
details are coming in the next few days as models better align on
timing and precipitation amounts.

&&

.AVIATION...
212130Z...VFR will prevail. Mid level clouds will continue at
7000- 10000 feet this evening. Ceilings with bases of around 1500
feet MSL may affect the coastal basin after 04Z tonight,
especially at KCRQ and KSAN. Low confidence. Any low ceilings will
lift after 12z Thu.

&&

.MARINE...
Northwest winds and seas will increase Wednesday and continue
through Thursday. A swell from 280-290 degrees will build in on
Wednesday, peaking at 8-12 feet late Wed afternoon and evening with
a period of 14 seconds. The increasing winds and building swell will
result in hazardous boating conditions and a Small Craft Advisory
is in effect Wednesday through early Friday.

&&

.BEACHES...
Increasing westerly swell will bring high surf Wednesday and
Thursday. The swell will come in from 280-290 degrees at 14 seconds,
producing high surf late Wednesday with sets reaching 8-10 feet.
A High Surf Advisory is now in effect Wednesday through Thursday
night.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 1 PM Wednesday to 1 AM PST Thursday for Apple
     and Lucerne Valleys-Riverside County Mountains-San
     Bernardino County Mountains-San Diego County Deserts-San
     Diego County Mountains-San Gorgonio Pass Near Banning.

     High Surf Advisory from 7 AM Wednesday to 2 AM PST Friday for
     Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...Small Craft Advisory from 7 AM Wednesday to 2 AM PST Friday 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...JJT
AVIATION/MARINE/BEACHES...Gregoria



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