Area Forecast Discussion
Issued by NWS San Diego, CA

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276
FXUS66 KSGX 200448
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Tue Mar 19 2019

.SYNOPSIS...
Mostly cloudy conditions will occur tonight as a low pressure system
approaches from the west. Cooler weather will prevail Wednesday
through Thursday with periods of showers and mountain snow, and a
slight chance of thunderstorms Wednesday afternoon and early
evening. Fair and a little warmer weather will return Friday. The
next low pressure system will bring a chance of mostly light showers
on Saturday. Dry with a warming trend will occur early next week.

&&

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

Clouds, both high and low, were increasing this evening, and radar
was showing some precipitation echoes aloft. The NKX sounding late
this afternoon showed a dry layer from just above the 1500 foot
marine layer inversion up to about 550 MB, so a lot of the
precipitation aloft will evaporate before reaching the surface. The
first hint of organized precipitation should be early Wednesday
morning along the coast. Overall, there is not much change in the
forecast of this storm as most of the precipitation will be light,
but local rain rates up to 0.40" per hour are possible in heavier
showers or isolated thunderstorms due to the instability from the
cold core which will move over most of California. A second wave
late Thursday should bring some additional precipitation, but
overall, most locations west of the mountains should remain below
0.50" for Wednesday through Thursday, with local amounts up to
around one inch in the San Bernardino County Mountains. Snowfall of
3-6 inches is possible above about 6500 feet in SBD County, with
lighter snowfall down to the approximately 5500 foot snow level.

From previous discussion... A low pressure system currently at about
125 west longitude will move through SoCal Wednesday and Thursday.
It will bring lower temperatures, increasing clouds, gusty westerly
winds and periods of showers Wed through Thu. Showers will move in
from the west on Wednesday morning. Most of the precip will fall
between early Wed morning and Wed evening, decreasing thereafter.
Isolated to scattered showers will continue through Thursday. Cold
air advection aloft and increasing instability will bring a chance
of thunderstorms Wed afternoon and evening. Current rainfall
estimates are for 0.15-0.25 inch near the coast, 0.30-0.75 inch in
the mtns and less than 0.25 inch in the deserts.

Snow levels will be 5500-6500 feet Wed morning and early
afternoon, lowering to 5000-5500 feet for Wed night into Thu
morning. Snowfall amounts of 2-4 inches are expected above 5000
feet and up to 6 inches above 6000 feet.

Winds will strengthen from the west early Wed morning, peak Wed
evening and weaken Thu morning. Wind gusts of up to 45 mph will be
possible on the desert slopes of San Diego County and the
Coachella Valley.

A cooling trend that began today will continue through Thursday
which will be the coolest day, with daytime temperatures in the 50s
to low 60s at lower elevations west of the mtns.

Fair and warmer on Friday as a dynamic upper-level ridge moves in
from the west. Daytime temperatures will be mostly in the mid 60s
at lower elevations west of the mtns. Another low pressure system
moving inland to the north on Sat will bring cooler and unsettled
weather. This will be a relatively fast-moving system so precip is
expected to begin Sat morning and end by Sat evening. SoCal will
be on the southern periphery of this system so only small amounts
of precip is expected.

After this system moves inland to the northeast, a building ridge
of high pressure over the western U.S. will bring dry weather and
a warming trend. Daytime temperatures are expected to return to
near seasonal averages by early next week.

&&

.AVIATION...
200345Z...Coasts/Valleys/Mountains...Areas of low clouds with bases
2000-2500 ft MSL will continue along and west of the mountains
through about 12Z. After 12Z...SCT-BKN cloud layers with bases 2500-
5000 ft MSL with tops to 8000 ft MSL with SCT -SHRA through
Wednesday evening, along with a slight chance of -TSRA in the
afternoon. Vis may be locally reduced to 3-5 SM in heavier
showers/thunderstorms. Coastal mountain slopes will remain obscured.

Mountains/Deserts...West SFC winds 15-20 kts gusting to 35 kts over
the mountain crests, desert mountain slopes, and through the passes
through early Wednesday morning, and again Wednesday afternoon and
evening. MOD UDDFTS likely over and east of the mtns at times. ISO-
SCT -SHRA possible Wednesday afternoon with increasing clouds AOA
7000 ft MSL.

&&

.MARINE...
A weak storm will bring west winds gusting 15-20 kt and higher seas,
along with showers Wednesday through Thursday. There is a slight
chance of thunderstorms Wednesday afternoon and evening. Another
weak storm may bring additional light showers on Saturday.

&&

.BEACHES...
A swell of 7-8 ft at 14-16 sec from 280 degrees will generate high
surf of 3-8 feet Wednesday afternoon through Friday morning, highest
in southern San Diego County. Swell and surf will subside on Friday.
Another larger west-northwest swell may bring additional high surf
this weekend.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 5 PM Wednesday to 8 PM PDT Thursday
     for Riverside County Mountains-San Bernardino County
     Mountains.

     High Surf Advisory from 1 PM Wednesday to 1 PM PDT Friday for
     Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

$$

PUBLIC...Maxwell/PG
AVIATION/MARINE/BEACHES...SS



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