Weather

378 
fxus66 ksgx 281715 cca 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
1015 am PDT Thursday Aug 28 2008 


Corrected synopsis 


Synopsis...a deep marine layer will keep skies mostly cloudy at the 
beaches today but the marine layer will shrink on Friday and mostly 
sunny days are likely for the beaches this Labor Day weekend. 
Increasing monsoon moisture will bring a return of thunderstorms 
Friday and Saturday. Some of these may move west of the mountains 
and across the valleys and coast Friday night and Saturday. Drier 
and more stable air will move over the region Sunday and Labor 
Day. Next week an upper level trough will bring slight cooling and a 
return of the marine layer. 


&& 


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


Short term...today through Saturday... 
monsoon moisture pulsing towards SW California but all factors not 
quite in alignment today to generate thunderstorms over 
mountains/deserts. The remnant circulation from the mesoscale scale 
convective complex that was over northwest Arizona last night is currently 
moving west southwestward around 12 kts across Imperial/eastern San 
Diego County. This feature should turn more towards the west later 
this morning across San Diego County and then northwest this 
afternoon as it moves over the coastal waters and continues its 
path around the periphery of the high cell to the north. In its 
wake convergence aloft will generate downward motion which should be 
sufficient to offset the low/middle level convergence over the 
mountains this afternoon. Also trigger temperatures will be quite high...93 
for 5000 feet and 103 for 3500 feet...so only moderate cumulus at 
worst expected over higher mountains today. Plan to take advantage 
of this temporary break in active convection to install upgrades to 
wsr-88ds at ksox and knkx so they will be down for a few hours this 
morning. For tonight through Friday the low/middle level monsoon 
moisture increases to a depth of at least 10000 feet due to the 
increasing southeast flow. With no inhibitors in place...diurnal 
heating Friday should lead to scattered to widespread thunderstorms 
forming over mountains. For Friday night through Saturday with 
prevailing flow becoming more east due to shifting of high 
cell...thunderstorms should drift west of the mountains and any 
embedded short waves/remnant upstream circulation centers caught up 
in the flow could generate squall lines that would propagate 
westward across the valleys/coast/and coastal waters...somewhat 
analogous to this past Monday. Moving on to the more pressing 
question...when will the stratus clear. Marine layer is deeper and 
deepening this morning from weak lifting ahead of above mentioned 
circulation center. Rule of thumb using a 1000 foot cloud layer 
would say stratus not breaking up until 1020 PDT. A nam12 model 
cross section along the coasts shows the mean layer relative 
humidity in the lower 2000 feet staying above 90 percent along San 
Diego coast all day...with Orange County coast dropping down to 
around 75 percent for only a brief 3 hour period...between 1400-1800 
PDT...and then humidity rockets back up to +90 percent...closer to 
100 percent in lower 1000 feet after 2000 PDT. So looks like 
limited/late patchy clearing for San Diego coast today and early to 
middle afternoon clearing for Orange County coast...with hazy sunshine 
this afternoon for the valleys. Much better prospects for sunshine 
along the coast on Friday as increasing instability mentioned above 
will be spreading westward across the entire 
area...eroding/eliminating the capping inversion and mixing out the 
marine layer so stratus should break up much earlier on 
Friday...around 0900 PDT...and gone by 1000 PDT with no return 
Friday night/Saturday...or at worst patchy/scattered stratus 
confined to below 300 feet over water and South San Diego County 
coast/northern Baja California California. 


Long term...Saturday night through Wednesday... 
all models in agreement with relatively strong trough moving inland 
to the north Saturday night...resulting in increasing west to 
southwest winds and drier/stable air mass moving over southwest 
California Sunday through at least Monday and possibly lingering 
through remainder of next week. Marine layer should begin to rebuild 
by Sunday night aided by a coastal eddy circulation...however Labor 
Day likely to be mostly sunny at the beaches with any stratus/fog 
clearing well before 1000 PDT. After Monday a week upper low slowly 
approaches from the west southwest...and the resulting weak cyclonic 
flow aloft should aid in maintaining a coastal eddy and deepening 
the marine layer. Fair weather expected elsewhere. 


&& 


Aviation... 
271520z...marine layer stratus thickness this morning about 1k feet 
with bases near 1k feet mean sea level and tops to fl020. This solid marine deck 
should delay clearing at the coastal airports until around 19z 
time frame. Farther inland...expect the ceilings to lift between 16z and 
17z...although 3-5sm visible restrictions will continue in haze until 
around 20z. At the beaches...areas of ceilings/haze are likely to linger 
through the afternoon. Above the marine layer visible will be 
unrestricted with some scattered to locally broken clouds at fl150. 






&& 


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


&& 


$$ 


Public/fire weather...Balfour 
aviation/marine...jad 


National Weather Service on the web at weather.Gov/sandiego