084 
fxus66 ksgx 211702 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
900 am PST Sat Nov 21 2009 


Synopsis...residual moisture will continue areas of low clouds and 
patchy dense fog west of the mountains this morning...then patchy 
coastal low clouds tonight. Otherwise...mostly clear. Cool today 
with windy conditions in the mountains and deserts. Warmer through 
the middle of next week under high pressure with weak offshore flow. 


&& 


Discussion...for southwest California including San Diego... 
Orange...southwest San Bernardino and West Riverside counties. 


Today through Monday...patches of low clouds and fog linger west of the 
mountains this morning with variable high cloudiness. The morning 
nkx sounding indicated an inversion at about 2500 feet with westerly 
winds above. Pressure gradients continue onshore with about 4 mb 
san-ipl and 7 mb san-las. 


The upper trough moving off to the east will leave behind a little 
low level moisture for low clouds and patchy fog west of the mountains 
this morning. There could also be patchy coastal low clouds and fog 
tonight and variable high cloudiness through Sunday. Locally windy 
in the mountains and deserts today. Dry northwest flow with slowly 
increasing heights will develop later today and continue through 
Sunday. Cool today with maximum temperatures about 3 to 7 degrees below 
seasonal averages in most areas. Surface pressure gradients will become 
weakly offshore to the north for a brief period tonight into Sunday 
morning...but remain onshore to the east. This will have little 
effect except to lower humidities a little in the northern areas. 
Clear and warmer Monday under high pressure with weak offshore flow. 


Tuesday through Saturday...upper level ridging and weak offshore 
flow will continue through middle week. This will maintain generally 
clear skies with a warming trend. Thursday should be the warmest day 
in most areas with maximum temperatures about 5 to 10 degrees above seasonal 
averages in the inland valleys and foothills. There will be local 
gusty winds through and below mountain canyons and passes at times 
but they are expected to remain below advisory strength with most 
gusts less than 35 miles per hour. Cooler Friday and Saturday as a low pressure 
trough moves through to the north and onshore flow returns. 


&& 


Aviation... 
211600z...marine layer about 3k to 3.5k feet. Areas of broken bases 
around 2.5k to 3k feet mean sea level. Expect stratus to clear by 18-20z with a 
few stratocu possible in the afternoon. Visibility quite variable with 
areas 3-5sm...locally 1-2sm and isolated below 1sm. Visibility will 
improve by 16-17z. Expect mostly clear with local visibility 3-5sm and 
isolated below 3sm late tonight through about 1630z Sunday 
morning...otherwise mostly clear tonight through Sunday. 


&& 


Fire weather... 
no short term fire weather concerns now that marine layer has 
deepened and spilled into deserts although still quite dry above 
7000 feet. Next concern is high pressure rebuilding over the 
northern Great Basin Sunday night through at least Tuesday morning 
for return of offshore flow. The pressure gradients that are 
forecast to develop between NE Nevada and SW California coast are 
significant...14-18 mb...but the upper level ridge appears quite 
broad with an axis too far inland to indicate more than weak upper 
level support. So feel that the local wind program output from the 
21/00z GFS model is overdone and European model (ecmwf) may also be...showing most of 
next week with wind gusts in excess of 35 miles per hour wind prone areas. At 
this time leaning more towards sustained NE-east 10-15 miles per hour with gusts 
in the 25-35 miles per hour range. Monday will likely still be cool and moist 
enough to keep humidity at most locations above 15 percent. Current 
forecast for Tuesday has 6 to 8 hours of humidity below 15 percent 
for inland valleys/foothills/mid slopes with poor overnight recovery 
Tuesday night above 1500 feet elevation. On Wednesday longer 
durations...8 to 12 hours with poor overnight recovery again. 
Thursday durations of low humidity similar to Tuesday. Friday the 
ridge breaks down yielding cooling and moistening trend as onshore 
flow returns. 


&& 


Sgx watches/warnings/advisories...none. 


&& 


$$ 


Public...pg 
aviation...Whitlow 
fire weather...Balfour