000 
fxus66 ksgx 180359 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
855 PM PDT Fri Aug 17 2018 


Synopsis... 
high pressure aloft will bring another hot Summer weekend to the 
region. Relief from the heat will be found at the coast and in the 
higher mountains where temperatures will be closer to average. 
Monsoon moisture will return early next week with chances for 
afternoon thunderstorms over the mountains and deserts Tuesday 
through Thursday. 


&& 


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


Thunderstorms over the mountains this afternoon were not as 
widespread as yesterday, but a strong one formed over the Cranston 
fire burn scar and dropped about an inch of rain in 1 hour. It 
resulted in flash flooding and debris flows in the burn area, and 
prompted the closure of Highway 74. 


The storms dissipated by early evening and that should be the end of 
our thunderstorm threat for a couple days as drier air associated 
with strong high pressure aloft builds over Southern California. 
There will be downward trend of atmospheric moisture this weekend. 
The precipitable water over the mountains of 1.30" today lowers to 0.80" Saturday, 
then rises slightly Sunday to 0.90". Synoptic scale subsidence with 
the high aloft coupled with a drier atmosphere will limit the 
cumulus growth over the mountains each afternoon. 


On Monday, the upper ridge moves east over Arizona and nm and that will 
reestablish a south to southeasterly monsoon return flow into socal 
next week. The precipitable water Monday rises to 1.10", then to 1.20" Tuesday and 
Wednesday, and then to 1.40" Thursday. This is reflected in the 
forecast that has incrementally increasing thunderstorm coverage 
over the mountains and deserts each day. The storms will drift north- 
northeast off the mountains and into the deserts due to prevailing 
south-southwest above 500 mb. 


Night and morning coastal clouds will spread across the coastal 
areas and into the western valleys each day. It'll be another very 
warm/hot stretch of weather through the middle of next week, but 
it's August so that's not all that surprising. 


&& 


Aviation... 
180400z...coasts/valleys...bkn/ovc stratus will gradually spread up 
to 30 miles inland overnight, including far west and south parts of 
the inland Empire. Bases will be 1300-1700 ft mean sea level with tops to 2000 
ft msl, and higher terrain will be locally obscured. Local vis below 
3 miles will occur in the valleys due to fog, 09z-15z Sat. Most 
areas will clear by 17z Sat, except for local broken cigs remaining 
near the beaches through Sat afternoon. 


Mountains/deserts...few-sct clouds at/above 10000 ft mean sea level with 
unrestricted vis will prevail through Saturday. 


&& 


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


&& 


Beaches... 
beach hazard statement will continue through Saturday for elevated 
surf and strong rip currents. A 4 ft/16-17 second period swell from 
180 degrees will bring surf of 3-6 ft, with isolated sets to 9 ft, 
mainly along the south facing beaches of northern Orange County, and 
strong rip currents. Surf will lower Saturday night through Sunday. 


&& 




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


&& 


Sgx watches/warnings/advisories... 
California...beach hazards statement through Saturday evening for Orange 
County coastal areas-San Diego County coastal areas. 


Pz...none. 


&& 



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