Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 222236
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
236 PM PST Wed Feb 22 2017

.SYNOPSIS...
The back side of a trough will continue to bring cool but dry
conditions to Southern California along with strong winds in the
mountains and deserts through Thursday morning. The trough will
depart the area on Thursday with tranquil weather under plenty of
sunshine Thursday through Friday. Cloudiness will increase on
Saturday ahead of a trough forecast to move down the coast of
California on Sunday. This trough will bring a round of showers
to the area Sunday through Sunday night. Another trough will move
in from the west on Monday. This trough will bring greater
moisture into Southern California, possibly bringing more
substantial precipitation to the area Monday. The trough will
depart the area with improving weather conditions Tuesday through
Wednesday.

&&

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

Highlights...

* Dry and Seasonably Cool Through Saturday

* Showers Arrive on Sunday; More Substantial Precipitation
  Possible Monday

The backside of a trough is situated over California. This is
producing strong westerly winds from the mountain ridges to the
desert mountain slopes and onto portions of the desert floor. Have
extended the Wind Advisory for these locales through Thursday
morning.

Low stratus and fog became fairly widespread early this morning.
However, as low level moisture decreases, do not anticipate
similar conditions overnight. Followed the WRF RH depiction,
showing fog confined overnight/early Thursday to the inland
valleys and the coastal mountain slopes of San Diego County.

Fair weather with more sunshine is forecast Thursday through
Friday. Cloudiness will gradually increase on Saturday ahead of a
trough moving down the U.S. west coast.

Both GFS and ECMWF have changed solutions with regards to how
troughs will move/interact with each other Sunday-Monday.
Yesterday, both models depicted a trough moving in from the
Pacific Northwest and phasing with a trough over the Pacific.
However, GFS/EC have trended to show no phasing occurring with the
first trough. This results in a solution of one weak trough
moving down the coast on Sunday and more of an inside slider, so
while showers are still expected on Sunday, it is looking less
widespread and less significant. However, another separate trough
over the Pacific is shown to be delayed and move into Southern
California on Monday, this perhaps phasing with yet another
shortwave diving south from the Pacific Northwest. This would
bring more substantial precipitation to Southern California as it
pulls an Atmospheric River/AR briefly into the area ahead of it.
Trended POPS slightly lower for Sunday and slight higher for
Monday given these trends.

The degree of moisture entering the area ahead of the trough
Sunday night-Monday is in question and thus there is low
confidence on how much precipitation will fall. Very preliminary
precipiation totals Sunday-Monday from WPC stand at 0.75-1.5
inches from the coast to the valleys with 2-3 inches on the
coastal mountain slopes of the San Bernardino County mountains.
There is high spread in the GEFS with the ensemble mean
significantly lower than the operational run, so verdict is out on
how much precip will fall, but substantial precipiation is
a possibility on Monday.

It looks to be colder in the mountains compared to our last storm
as the first trough pulls in some colder air. Preliminary snow
levels are somewhere in the 4500-5500 range during the precip
Sunday-Monday.

The trough will depart the area Tuesday-Wednesday with dry weather
returning behind it.

&&

.AVIATION... 222130Z...Coasts/Valleys...SCT/BKN low clouds, with
bases 2000-4000 ft, this afternoon with slow clearing this evening
from north to south. Patchy FG/BR with VIS 2-4 SM possible early
tonight in the valleys of San Diego County. VFR conditions expected
late tonight through Thu.

Mountains/Deserts...W/NW surface wind gusts of 35-55 kt will
continue over areas through Thu morning. Strongest winds will occur
on the ridges/upper desert slopes of the mountains, below passes and
canyons, and where mountain waves surface in the deserts. STG-SVR
UDDFS and areas of LLWS likely over and E of the mountains. Winds
will slowly weaken late Thursday morning.

&&

.MARINE...
NW wind gusts of 25-30 kt will continue over portions of the waters
through Thursday night. A westerly swell from 275-285 degrees will
build today, and peak at 8-12 feet/14 sec this evening. Gusty winds
and large/steep seas will result in hazardous boating conditions. A
Small Craft Advisory remains in effect through Thursday night.

&&

.BEACHES...
A building westerly swell from 275-285 degrees will create high surf
along westerly-facing beaches through Thursday night. This will
result in surf of 5-8 ft with sets to 10 ft. A High Surf Advisory
remains in effect through Thursday night for dangerous surf and
strong rip current.

&&

.SKYWARN...
SKYWARN activation will not be needed through Saturday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 10 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 until 2 AM PST Friday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...Small Craft Advisory until 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...Gregoria
AVIATION/MARINE...JJT



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