Weather

183 
fxus66 klox 280512 
afdlox 


Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
1010 PM PDT Wednesday Aug 27 2008 


Short term (tonight-sat)...the marine layer was around 1100 feet deep 
at lax this evening. Low clouds were more widespread this evening 
over the coastal waters than last evening...with low clouds and fog 
beginning to move inland along the central coast...and most coastal 
areas S of Point Conception. Ceilings and visibilities were lower this 
evening...with some reporting stations indicating visibilities down to 1/2 
mile. Added local dense fog tonight to the coastal areas S of Point 
Conception for tonight...but with the marine layer expected to 
increase some overnight...the chance of any dense fog Thursday morning is 
minimal. Patchy low clouds and fog should move into the valleys 
later tonight as well. Otherwise mostly clear skies can be expected 
over the region through the night. 


The evening models are in decent agreement with the large scale 
features Thursday through Sat. An upper hi will expand into California from off the 
coast Thursday...then build eastward into the southern Great Basin for 
Friday. A broad upper trough will move into northern and central California by late 
Sat. In addition...an inverted upper trough should move just to the S 
or southeast of the forecast area on Sat. The middle level flow over the 
district should be generally easterly through Thursday then turn more NE on 
Friday and generally variable for Sat as the region will be under a col 
area between the upper high to the east and the upper trough approaching 
from the northwest. The latest model runs scaled a bit back on the amount 
of middle level moisture moving into the region during the 
period...although precipitable water increases to over an inch and a 
third along and S of the l.A. Coast by Sat. Precipitable water levels remain 
generally less than an inch over the mountains and Antelope Valley. 
At this time it appears the chance of any thunderstorms over the 
mountains and Antelope Valley will be minimal Friday through Sat...but for 
now will not change the forecast of a slight chance there during the 
period as model consistency from run to run with regard to moisture 
has been somewhat marginal. Otherwise the marine layer should be 
about 1100 to 1300 feet through Friday then lower some by Sat to below 1000 
feet. Varying amounts of low clouds and fog will persist mainly along 
coastal areas through Sat. Extensive hi clouds will be possible over 
the district on Sat as well. Temperatures over the region are expected to 
be generally near normal to slightly above normal during the period 
for coastal and adjacent valley areas...and well above normal for 
the most part well inland. 


..from previous discussion... 


Long term (sun-wed)...both the 12z European model (ecmwf) and GFS show a fairly deep 
trough dipping into central California on sun...and although the Euro model 
is slightly faster...both models have been fairly consistent for the 
last 24 hours or so. This trough will not bring any moist frontal band 
to the area...but will help to push the ridge that was parked over 
central California on Friday and Sat to the east on sun. Deep layer flow will 
shift to a dry westerly regime rather abruptly...and kill any 
threats of afternoon convection. High pressure will also build over 
the waters off the coast...which should also increase westerly flow. 
This all adds up to a rather quick and steep cool down sun and 
Monday...with a few breezy spots along the coast and the mountains the 
marine layer should also assert itself deeper into the valleys. Once 
the trough moves through...temperatures will bump back up on Tuesday and 
Wednesday...with a return to near normal conditions. 


&& 


Aviation...28/0500z...hi confidence low clouds and LIFR to IFR 
conditions will affect the coastal taf sites overnight and Thursday 
morning. Low to moderate confidence any low clouds and LIFR 
conditions will affect kbur and kvny late tonight and early Thursday. 
Otherwise VFR conditions will prevail through Thursday. 


For klax...hi confidence low clouds and LIFR to IFR conditions will 
affect the airfield overnight through about 18z Thursday then VFR the rest 
of the day. No wind issues are expected through Thursday. 


For kbur...low to moderate confidence any low clouds and LIFR 
conditions will affect the airfield late tonight and early 
Thursday...otherwise VFR conditions can be expected. No wind issues are 
expected through Thursday. 


&& 


Lox watches/warnings/advisories... 
none 


&& 


$$ 


Public...sirard/kittell 
aviation...sirard 


Www.Weather.Gov/losangeles