923 
fxus66 ksgx 231705 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
900 am PST Monday Nov 23 2009 


Synopsis...high pressure aloft and weak offshore flow will bring 
fair weather with a warming trend through Thanksgiving day. Cooler 
with increasing clouds toward next weekend as a low pressure trough 
approaches from the northwest. 


&& 


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


Today through Thanksgiving day...shallow patchy fog west of the mountains 
has already burned off this morning. Surface pressure gradients have 
turned offshore to the north and east with about 10 mb san-tph and 1 
mb san-ipl. 


An upper level high pressure ridge and a surface high over the Great 
Basin will bring fair skies...offshore flow...much warmer weather 
and local gusty winds below the passes and canyons through 
Thanksgiving day. Incremental increases in 500 mb heights and 850 mb 
temperatures will result in a few degrees of warming each day...with 
daytime highs reaching about 10 degrees above seasonal averages by 
Thanksgiving day. Skies will be mostly clear as dry offshore flow 
scours out the marine layer. 


The offshore flow will be driven primarily by surface pressure 
gradients...with little upper level support and only weak to 
moderate surface pressure gradients. Wind gusts below the passes and 
canyons will generally remain below 30 miles per hour...however 
isolated/occasional gusts from 40-50 miles per hour are possible in the most 
wind-prone locations. The strongest winds are expected Tuesday 
morning when the pressure gradients are strongest. 


Very dry air is expected with the offshore flow this week. Inland 
humidities will fall below 10 percent each day beginning Tuesday and 
continuing through Thursday. The combination of locally breezy 
conditions and very low humidities will elevate the fire weather 
hazard. 


Friday through Monday...the GFS and European model (ecmwf) forecasts for later this week 
are coming into better agreement and show the ridge breaking down 
Friday ahead of a deepening low pressure trough that will bring 
increasing clouds and substantial cooling through Saturday. As this 
trough moves to the east on Sunday and Monday...a colder and 
potentially windy offshore pattern could develop. 


&& 


Aviation... 
231600z...clear through Tuesday with thin high clouds at times. 
Northeast winds 15-25 knots over the mountains and inland valleys 
through passes and canyons with moderate turbulence late tonight 
through Tuesday morning. 


&& 


Sgx watches/warnings/advisories...none. 


&& 


$$ 


Public...pg 
aviation...Whitlow