000 
fxus66 ksgx 242051 
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Area forecast discussion 
National Weather Service San Diego California 
151 PM PDT Mon Sep 24 2018 


Synopsis... 
high pressure aloft will build in from the west and eventually 
overhead Southern California by Thursday. This will lead to 
building heat inland Wednesday through Thursday. For Friday into 
the upcoming weekend, an upper level low off the West Coast will 
move inland into northern California, bringing stronger onshore 
flow and a cooling trend for Southern California. 


&& 


Discussion...for extreme southwestern California including Orange... 
San Diego...western Riverside and southwestern San Bernardino 
counties... 


The marine layer stratus has hung in tough over San Diego County 
today with clouds socked in here even at the office in rb this 
afternoon! Even some light mist/drizzle has been observed here 
and reported elsewhere. GOES satellite loop does show thinning 
of the cloud deck occurring, so some sun is possible where it is 
currently cloudy, though looking less likely than earlier 
anticipated. 


The stratus deck will move inland again some 25 miles and over 
Orange County into northwestern parts of the inland Empire. Again, 
patchy drizzle will be possible. WRF shows clouds again slow to 
clear on Tuesday and have followed this trend. 


Heights will be rising as an upper level ridge builds in from the 
west and eventually becomes centered over Southern California by 
Thursday. This will lead to warming temps with hot conditions 
inland Wednesday-Thursday. Heat risk doesn't support heat 
headlines, but have increased high temperatures Wednesday-Thursday 
with some triple digits for parts of the inland Empire and to 
around 110f for the Coachella Valley. The coast will peak at near 
80f with inland oc Metro and the inland valleys of South Dakota into the 
lower to mid 90s. 


An upper level low will cut off and approach the California coast 
by Friday and eventually move across norcal this weekend. This 
will displace the upper ridge to the southeast with lowering 
heights across socal. So gradual cooling is expected Friday and 
into the weekend, but still remaining slightly above late 
September averages. Winds could become gusty and locally strong on 
the Desert Mountain slopes and portions of the deserts each 
afternoon and evening this weekend. 


The weather for the first week of October is certainly interesting 
to look at but is highly uncertain. Several runs of the GFS are 
pulling a tropical system north into northern baja centered 
around October 2nd, while the European model (ecmwf) keeps the system south of 20n. 
A look at the 24.00z GFS ensemble runs shows that 4 of 12 members 
bring some tropical moisture into socal. Given that the ensemble 
mean keeps the tropical moisture away, along with the ECMWF, am 
favoring this scenario. However, we of course will continue to 
monitor this in the days ahead for better model continuity. 


Interestingly, while the 24.12z run of the European model (ecmwf) continues to keep 
the tropical systems locked well to the south, it actually does 
show some light rain over socal early next week, but not from the 
tropics, rather a deep Pacific trough. 


&& 


Fire weather... 
weak offshore flow will begin Tuesday and last through Thursday. 
Easterly winds will prevail with gusts to about 20-25 mph over the 
mountains and coastal mountain slopes, as well as through the 
passes, but weaker winds are forecast for lower elevations. The 
westerly sea breeze will kick in each day. Still, relative 
humidity will lower with rhs in the teens into the inland Empire, 
the far easterly San Diego County valleys as well as over the 
mountains and deserts, resulting in elevated fire weather concerns 
during this period. By Friday, winds will become onshore with 
gradually modifying rhs, except across the deserts. 


&& 


Aviation... 
242000z...coast/valleys...a solid overcast persisted over ksan and 
kcrq this morning with pilots reporting bases near 1300 feet and 
tops near 2800 ft. Drizzle was reported in some areas. Cigs will 
likely continue at ksan and kcrq through tonight, but a brief period 
of clearing is possible today between 22z-02z. 


Skies cleared at ksna at 19z, but low clouds will return between 02- 
05z with bases from ovc012-015 tops 027 will will move back inland 
this evening and reach kont between 10-12z. 


The low clouds Tuesday morning will be slow to clear back to the 
coast Tuesday afternoon with ceilings at ksan and kcrq through 21z. 
There will also be pockets of drizzle. Vis at kont will be 2-4 miles 
in haze through 19z Tuesday. 


Mountains/deserts...mostly clear with unrestricted through 
Wednesday. 


&& 


Marine... 
no hazardous marine weather is expected through Friday. 




&& 


Sgx watches/warnings/advisories... 
California...none. 
Pz...none. 
&& 



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