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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 181023

Area Forecast Discussion
National Weather Service San Diego CA
323 AM PDT Sat Aug 18 2018

Upper level high pressure has built in from the north and will
strengthen over the area today. There is still enough moisture
present for the possibility of a few showers developing over the
mountains this afternoon. Moisture will decrease a bit more 
Sunday through Monday for the expectation of tranquil weather
conditions before monsoonal moisture returns during the middle
part of next week, promising a return to afternoon mountain and 
desert thunderstorms. 



Water vapor imagery shows a shortwave departing through the
intermountain west with upper level ridging building in overhead

Hi-res models are dry today with the WRF showing no cell 
development anywhere today. HRRR shows a small light cells over
the Riverside mountains. Moisture levels are still sufficient 
under the upper ridge. In fact, satellite-derived Precipitable 
Water shows values ranging from 1.6 inches near the border to 
1.2-1.4 inches across the mountains, highest south. Some 
instability develops along the mountain crests this afternoon 
with MUCAPE values of 500+ J/KG. These parameters suggest some 
cumulus will develop over the mountains this afternoon with even 
the potential of isolated showers. However, the suppressing ridge 
should inhibit thunderstorm development. No flash flooding is 

Tranquil days are expected Monday-Tuesday. Kept the forecast dry,
but there still could be just enough moisture present for cumulus
if not a few showers developing in the mountains. We can see the
latest hi-res runs and see how activity fares today to adjust the
forecast as needed. Either way, no significant impacts are
expected with no flash flooding anticipated through Monday.

Models show monsoonal moisture increasing Tuesday-Thursday, as the
upper high shifts east. This will bring a return to afternoon 
mountain and desert thunderstorm activity then. How active it gets
though is uncertain and will assess in the days ahead. 

Nighttime and morning low cloudiness will dominate at the coast
each day with sunshine each afternoon. It will continue humid as
well. Temps will continue to run above average through next week,
but not to excessive levels. 


180940Z...Coasts/Valleys...Low clouds with bases 1200-1800 ft MSL 
and tops to 2100 ft MSL spreading up to 25 mi inland through the 
morning. Most areas will clear by 18Z Sat, except for local BKN cigs 
along the immediate coast through the afternoon. Clouds will 
redevelop and spread inland after 19/01Z with bases 1100-1600 ft 
MSL. Otherwise mostly clear with unrestricted vis through Sunday 

Mountains/Deserts...Cumulus developing over the mountains this 
afternoon with bases near 10000 ft MSL. There is a slight chance of 
showers over mountain crests. Otherwise mostly clear with 
unrestricted vis through Sunday morning.


No hazardous marine weather is expected through Wednesday.


Beach Hazard Statement will continue through this evening for 
elevated surf and strong rip currents. A 3-4 ft/15-16 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 tonight through 


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


CA...Beach Hazards Statement through this evening for Orange County 
     Coastal Areas-San Diego County Coastal Areas.