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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 161809

Area Forecast Discussion...UPDATED
National Weather Service San Diego CA 
Issued by National Weather Service Los Angeles/Oxnard CA 
1106 AM PDT Mon Sep 16 2019

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. 



.SHORT TERM (Today through Wednesday)... 
Latest visible satellite imagery showing a NE to SW band of
enhanced cloud tops stretching from around Long Beach 
southwestward to west of San Clemente Island. Lightning also 
detected in a cell south of San Nicolas and just recently west of 
San Clemente. Overall, however, lightning activity has decreased
last hour or so. Not much measurable precip is, or will be, 
associated with this area as it continues to move eastward toward 
the forecast district today...mainly sprinkles. Models showing 
most instability today right along the coast and much further 
inland. This lightning activity over the water this time of the 
morning is typical and not confident we'll see as much as it moves
further east today, and as evidenced by the most recent trend. 
Nonetheless, given what instability that's expected today, the 
slight chance of thunder in current forecast looks good. Main 
threat will be possible lightning coastal areas and the 
possibility of gusty winds and dry lightning with any activity 
further inland.

This activity is in advance of a trough of low pressure which is
moving inland into the western states today, also acting to cool
temperatures a good 5 to 10 degrees over yesterday's readings. Low
to mid level moisture streaming through the area should make for
partly cloudy skies most areas, but with plenty of periods of more
sun than clouds. More widespread night and morning coastal low 
clouds are expected for tonight through Wednesday extending inland
into the far western valleys. This first trough moves through 
today, then weak height rises Tuesday before another trough moves 
through the west on Wednesday. All this means temperatures will 
remain below normal in the short term with stronger onshore flow.


.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.


161800Z...Coast/Valleys...SCT-BKN mid and high clouds above 12000 
feet MSL. Isolated -SHRA possible until 00Z. MVFR CIGS return after 
04Z tonight coastal terminals with SCT-BKN MVFR CIGS for valleys. 

Mountains/Deserts...Mostly BKN high clouds at/above 15000 feet MSL 
with a slight chance of TS and CB bases above 10000 feet MSL through 
00Z. After sunset SCT high clouds. 


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


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