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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 121142

Area Forecast Discussion
National Weather Service San Diego CA
342 AM PST Wed Dec 12 2018

There will be some patchy coastal low clouds and some high clouds
early today. High pressure aloft and offshore flow will bring 
warming west of the mountains for Thursday with locally gusty 
northeast winds near the coastal slopes of the mountains. A little
cooler for Friday as onshore flow returns, then a little warmer 
for the weekend under weak high pressure aloft. A low pressure 
system will move inland through California on Monday with small 
chances for precipitation, then dry for Tuesday with the 
beginning of a warming trend.



.SHORT TERM (Today through Friday)...
Aircraft soundings from Tuesday evening showed a weak marine
inversion at around 1400 feet with satellite imagery showing some
very patchy stratus over the inner coastal waters, and adjacent
coastal areas inland to the western San Diego County valleys.
Satellite imagery also showed a few high clouds from a trough of
low pressure moving inland to the north. As that low pressure 
system moves from the Great Basin into the southern Rockies, 
surface high pressure behind it over the Great Basin will bring 
periods of gusty northeast to east winds for tonight into Thursday
along coastal mountain slopes into the inland valleys and below 
passes and canyons. Onshore flow will return on Friday as another 
trough of low pressure moves inland to the north.

High temperatures today will be similar to those of Tuesday with
warmer high temperatures west of the mountains on Thursday with
the offshore flow. Cooling will begin to spread inland on Friday
with a return of onshore flow.


.LONG TERM (Saturday through Tuesday)...
The weekend is expected to be a little warmer for most areas as
onshore flow weakens, possibly becoming weakly offshore for 
inland areas at times.

For Monday and Tuesday, the range of solutions among the global
models and their ensemble members has not changed much for the
weak low pressure system that will be in the vicinity of southern
California on Monday. The weaker and more inland solutions would
be mostly dry for southwest California, while the more amplified 
solutions briefly close off an upper lower near or just offshore 
of the California coast before moving it inland. Given that a 
subtropical plume of moisture with precipitable water values 
approaching one inch will be directed toward southern California, 
there would be greater potential with this scenario for more 
widespread precipitation. The intermediate scenario is one with a 
cold front and associated precipitation weakening as it moves east
and south of Point Conception with light precipitation possibly 
extending into portions of southwestern California for Monday 
afternoon and evening. The current forecast remains closest to
that intermediate scenario.


121000Z...Areas of low clouds based around 1500-2500 feet MSL will 
continue to randomly form and dissipate in coastal areas and western 
valleys this morning. Local vis 4-5SM with pockets of much lower vis 
inland. Mostly clear after 16Z. Patchy low clouds may redevelop 
after 02Z tonight, but confidence is low on timing and coverage.


No hazardous marine weather is expected through Sunday.


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