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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 210957

Area Forecast Discussion
National Weather Service San Diego CA
257 AM PDT Thu Jun 21 2018

Strengthening high pressure aloft will bring warming through
Friday with the marine layer and weak onshore flow keeping
coastal areas cooler with areas of night and morning low clouds
and fog. For the weekend...a low pressure system moving through 
the Great Basin will strengthen the onshore flow across Southern 
California deepening the marine layer and spreading cooling 
inland. There will be slow warming for Monday through Wednesday as
the onshore flow weakens. Another low pressure system will move 
to near the West Coast bringing a cooling trend for late next 



Strengthening high pressure aloft centered over northwest Mexico 
will bring warming through Friday. The marine layer has decreased
in depth to around 2000 feet with widespread stratus over the 
coastal waters covering all of the Orange County coastal plain and
extending inland into portions of the western valleys in San 
Diego County. With a strong marine inversion and weak onshore 
flow...clearing near the coast this afternoon may once again be 
slow or limited. The marine layer will be a little shallower for 
tonight into Friday morning with the coastal low clouds not 
spreading as far into the western valleys. 

For the weekend...a low pressure system moving inland through the
Great Basin will weaken the high pressure aloft over Southern
California and strengthen the onshore flow. This will spread
cooling inland. It will also deepen the marine layer with coastal
low clouds extending into the western valleys on Saturday 
morning...and into the inland valleys on Sunday morning.

For Monday through Wednesday of next week...the onshore flow will
weaken with slow warming and with the marine layer becoming
shallower. Another low pressure system moving to near the West
Coast will bring a cooling trend for late next week.


210930Z...Coast/Valleys...Stratus, with bases 800-1800 ft MSL and 
tops near 2000 ft MSL, will continue this morning along the coast 
and 15-25 SM inland. VIS of 3-5 SM BR will also continue for most 
inland valleys, with some areas less than 1 SM where low clouds meet 
terrain. Low clouds will clear across inland areas by mid morning, 
but will likely linger along the immediate coast throughout the day. 
Stratus will then redevelop over the valleys again this evening, 
with slightly lower tops and bases.

Mountains/Deserts...Mostly clear with unrestricted VIS through 
Friday morning. 


No hazardous marine weather is expected through Monday.


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


CA...Excessive Heat Warning from 11 AM this morning to 8 PM PDT 
     Friday for Apple and Lucerne Valleys-Coachella Valley-San 
     Diego County Deserts-San Gorgonio Pass Near Banning.