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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 161117
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
417 AM PDT Mon Sep 16 2019

.SYNOPSIS...
A trough of low pressure moving inland today and a second for
Wednesday will spread cooling inland with a return of night and
morning coastal low clouds and fog. There is also a slight chance
of thunderstorms into early this evening with little or no
rainfall expected. For Friday into next weekend, that second
trough of low pressure will weaken with warming trend. 

&&

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

.SHORT TERM (Today through Wednesday)...
A trough of low pressure will move inland into the western states
today with a second trough for Wednesday. This will bring stronger
onshore flow today and again Wednesday. This will spread cooling
inland today with the cooling continuing into Wednesday or
Thursday.

The marine layer is near 1200 feet deep. Areas of low clouds have
returned across the coastal waters into adjacent coastal areas 
with locally dense fog near the mesas in San Diego County. 

An area of shallow mid level moisture and elevated instability
will move into the area from the west this morning, then exit to
the southeast early this evening. Enhancement is evident in
satellite imagery from Los Angeles and Ventura Counties to the
southwest. Radar is showing an area of cells extending westward
from beyond Catalina Island. Some virga or sprinkles are possible.
There is also a slight chance of thunderstorms. Any thunderstorms
would mostly produce gusty winds and a few dry lightning strikes
with little or no rainfall. 

More widespread night and morning coastal low clouds are expected
for tonight through Wednesday extending inland into the far
western valleys.

&&

.LONG TERM (Thursday through Sunday)...
The trough of low pressure moving inland on Wednesday will
continue the cooling into Thursday, followed by a warming trend
for Friday into next weekend as the trough of low pressure
weakens. The marine layer will become shallower with night and
morning coastal low clouds not spreading as far inland.

&&

.AVIATION...
160900Z...Coast/Valleys...Mostly BKN high clouds at/above 15000 feet 
MSL will prevail today, decreasing tonight. There is a slight chance 
of TS with little or no rainfall with CB bases above 10000 feet MSL. 
Areas of low clouds and fog will occur near the coast through 16Z 
today. Bases will be 700-1100 feet MSL with tops to 1200 feet with 
local vis 3-5SM. Low clouds will return with more uniform coverage 
in coastal areas after 04Z tonight. Bases around 1200-1500 feet MSL. 

Mountains/Deserts...Mostly BKN high clouds at/above 15000 feet MSL 
will prevail today, decreasing tonight. There is a slight chance of 
TS with little or no rainfall today with CB bases above 10000 feet 
MSL. Vis will likely remain unrestricted.

&&

.MARINE...
There is a slight chance of cloud to water lightning today. 
Otherwise, no marine weather hazards are expected through Friday.

&&

.FIRE WEATHER...
A trough of low pressure will move inland into the western states
today with a second on Wednesday. This will strengthen the onshore
flow with stronger and gusty southwest to west winds in the
mountains and deserts during the afternoon and evening. These
gusty winds combined with lower inland humidity will elevate fire
weather conditions from the desert slopes of the mountains into
the deserts from mid afternoon through early evening today and
again Wednesday.

A shallow layer of mid level moisture and elevated instability
will bring a slight chance of thunderstorms into early this 
evening. Little or no rainfall is expected. Any thunderstorms 
could produce gusty winds and a few dry lightning strikes.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...17
AVIATION/MARINE...MM