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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 202016

Area Forecast Discussion
National Weather Service San Diego CA
115 PM PDT Tue Aug 20 2019

High pressure aloft will bring hot weather to the valleys and 
deserts through tomorrow. A weak trough will bring cooling Thursday 
and Friday along with a deeper marine layer. The weekend will be dry 
with seasonal weather for late August. 



Today was quite a bit hotter than yesterday in the valleys as
high pressure aloft forced cooler marine air out of the western 
valleys and replaced it with drier, hotter continental air. 
The mountains and deserts were also quite a bit warmer. In 
contrast, a 1,000 ft deep marine layer kept coastal temperatures 
relatively unchanged from yesterday. 

Here are the noon temperatures and dew points showing the 24-hour 
changes in temperature and moisture from the coast to the desert.  

             Temp(F)     Dew Point(F)
Chino         89 (+9)       30 (-30)
Riverside     89 (+9)       48 (-12) 
Ontario       87 (+7)       48 (-11)
Ramona        87 (+5)       55 (-2)

Thermal      107 (+7)       30 (-18)
Palm Springs 107 (+5)       28 (-9)
Apple Valley  94 (+4)       36 (-9)
Borrego      107 (+4)       26 (-7) 

Big Bear      83 (+2)       19 (-6)       
Julian        85 (+2)       33 (-2)

San Diego     75 (0)        64 (+4)
Encinitas     74 (0)        66 (+1)
Laguna Beach  75 (-1)       66 (+2) 

Skies were clear this afternoon but marine layer clouds will 
reform over the coastal waters and move into the coastal zones 
later tonight. The marine layer may be 100-200 feet shallower and 
may not reach as far into the San Diego Valleys as last night. Areas 
of dense fog are again possible in some of the inland valleys 
tomorrow morning. 

The heat will peak Wednesday, and an Excessive Heat Warning will 
be in effect for the deserts through 8 PM. Highs will be from 114 to 
118 in the lower deserts and from 104 to 108 in the high deserts 
east of Apple Valley.

Thursday and Friday will be a little cooler as a weak trough of low 
pressure moves inland across California. It will slowly deepen the 
marine layer with greater night and morning low cloud coverage.

Long Range: The long range ensemble GEFS and EPS runs have trended a 
little drier with the monsoonal moisture surging into the southwest 
Saturday through Tuesday. The synoptic pattern shows a flat, east-
west oriented upper ridge extending from central California to 
northern Texas suppressing most of the moisture south of the border. 
Temperatures will be near seasonal averages through the period.   


202015Z...Coast/Valleys...Mostly clear with unrestricted vis through 
this evening. Low clouds moving ashore after 07Z with bases 500-1000 
ft MSL, spreading 15-20 miles inland overnight in San Diego County. 
Low confidence in cigs impacting Orange County and KSNA. Reduced vis 
of 4-6 miles in fog where stratus meets higher terrain. Scatter out 
expected after 16Z Wednesday. 

Mountains/Deserts...Mostly clear with unrestricted vis through 


Northwest winds will briefly reach 20 kt near San Clemente Island 
this afternoon and evening. Otherwise no hazardous marine conditions 
expected through Saturday. 


Skywarn activation will not be needed this week. 


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