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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 181700

Area Forecast Discussion
National Weather Service San Diego CA
1000 AM PDT Thu Jul 18 2019

A weak trough of low pressure near the California coast will 
continue the slow cooling trend and slow deepening trend of the 
marine layer into Friday with not much change for Saturday. Areas
of night and morning low clouds will spread into portions of the
inland values and may be slow to clear in the afternoon for some
coastal areas. For Sunday through Wednesday, strengthening high 
pressure to the east will bring an influx of monsoonal moisture 
with increasing humidity for inland areas. Chances for 
thunderstorms, mainly near the mountains during the afternoons and
early evenings, will begin around Monday. The marine layer will 
become shallower for Sunday through the middle of next week with
night and morning coastal low clouds patchier and not spreading as
far inland.



At 9 AM, water vapor satellite showed a weak upper-level trough 
across the Pacific NW, an upper-level ridge over central AZ and 
central NM and south to southwesterly flow aloft across southern
CA. A quick update to the forecast was sent this morning to 
account for the inland clearing of the low clouds and fog. The 
overall pattern will continue below normal high temperatures and a
moderately deep marine layer through Saturday. Night/morning low 
clouds and fog will develop into the valleys each day with a few 
high clouds at times through the period.

Model ensembles are in relatively good agreement with an upper- 
level high setting up over the Four Corners region early to mid
next week, but then become more scattered with the overall pattern
late next week. This will help advect monsoonal moisture into our
area starting Monday, creating a slight chance of thunderstorms 
over the mountains in the afternoons/evenings Monday and Tuesday, 
with more scattered thunderstorms possible over the mountains and
deserts Wednesday and Thursday afternoons/evenings. A few storms 
may even develop across portions of the Inland Empire Thursday. 
An increase in surface dewpoint temperatures will make it feel a 
bit more humid than it has been recently, and keep low 
temperatures higher than what they have been. Increasing heights 
aloft will help high temperatures to reach near seasonal normals 
by Monday. Night/morning low clouds and fog will be restricted to 
the coast by the middle of next week as the marine layer becomes 
more shallow, and could create low visibility for the morning 
commutes along the coast through the period. 


181530Z...Coast/Valleys...Low clouds made it about 20SM inland with 
bases 800-1500 FT MSL and tops near 2000 FT MSL. Areas of VIS 3-5SM 
BR/HZ along the higher coastal terrain and along the inland extent 
of the stratus deck. VIS will improve and stratus deck will mix out 
from the valleys toward the coast 16Z-19Z, with only partial 
clearing along the immediate coast and offshore. BKN-OVC stratus 
will move inland 02Z-04Z with bases 1000-1400 FT MSL. There will be 
areas of VIS 3-5SM in BR/HZ along higher coastal terrain overnight. 

Mountains/Deserts...Clear with unrestricted VIS through tonight. 
Areas of west winds 20-25KTG35KT through and below passes and near 
the desert slopes late this afternoon through tonight.  


No hazardous marine weather expected through Tuesday.


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