682 
fxus66 klox 301205 
afdlox 


Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
350 am PDT Sat Aug 30 2008 


Short term...plenty of middle and high level clouds have spread into 
l.A. County...disrupting the stratus quite a bit...with only patchy 
low clouds and fog near the coast. From vtu County northward...low clouds 
and fog were confined to the coastal plain...and with a fairly low 
inversion...some dense fog has developed though not widespread enough to 
require advisories. With some cooling at 850 and 950 mb...maximum temperatures 
should be down a few degrees from those on Friday in most areas. 
Mountains of l.A. County and the Antelope Valley. That will have to be 
monitored closely...since upper level winds will be very weak...and 
if any storm develops...it will move slowly. 


A weak inverted trough was located across extreme Southern California and northern 
Baja California...and a weak vorticity lobe will push across the area today. 
While the best moisture and instability will likely remain to S 
and east of the forecast area today...precipitable water values will rise 
to between 1.3 and 1.5 today...slightly lower than had be forecast 
by previous model run. However...with lifted index values forecast to 
drop to between -3 to -5 across the mountains of l.A. And vtu counties 
and the Antelope Valley...blv at least isolated showers/thunderstorms will 
develop in those areas today. With very weak winds aloft...any thunderstorm 
will be slow moving...and potentially heavy rains raise a concern 
for flash flooding. Therefore...have issued flash flood watches for 
the mountains of l.A. And vtu counties and the Antelope Valley from late 
this morning through this evening. Have decided to leave slight 
chance probability of precipitation in place for the valleys of l.A. Counties...although middle 
level winds on the latest run of the WRF appear somewhat less 
favorable to allow showers to drift into these areas. 


An trough will move into the Pacific northwest tonight and Sunday. Winds aloft 
will turn southwesterly tonight...pushing monsoonal moisture to the east of 
the area. Expect the marine layer to deepen tonight/Sun 
morning...with widespread night through morning low clouds and fog in 
coastal areas...probably spreading into the valleys. As 
heights/thicknesses fall and onshore flow increases there will be 
significant cooling across the entire area on Sunday...with temperatures in 
some valley locations probably remaining in the 70s. It will become 
quite windy in the Antelope Valley on Sunday. 


A strong vorticity dropping southward on the western side of the upper trough will 
cause it to dig southward through the Pacific northwest Sunday night...with a closed 
upper low over northern Nevada by Monday morning. Latest models are not 
quite as vigorous with this vorticity and do not show quite as much 
digging with this system. However...northwesterly flow will continue to increase 
across the outer coastal waters...and the WRF shows a fairly 
prominent eddy circulation developing Sun night. North-S grads across slow and 
sba counties may reduce low cloud coverage there...and some gusty 
winds are possible through and below passes and canyons of southern sba 
counties. With cyclonic flow aloft...strong west-east onshore grads and 
an eddy circulation...expect widespread low clouds and fog in coastal and 
valley sections of Los Angeles and vtu counties Sun night/Monday 
morning...and with the fairly deep marine layer and the eddy 
circulation...some local drizzle is possible. Temperatures will likely be up a 
few degrees across much of slow and sba counties on Monday...but do 
not expect much change S of pt Conception...with temperatures remaining 
several degrees below normal. 




Long term...the upper low trough move eastward Monday night and Tuesday...and 
height will rebound across the area. Expect a reduction in the night 
through morning stratus as least in the valleys as grads trend 
offshore. However...latest models were less bullish with the 
offshore trends and with height rises...so although warming is 
likely on Tuesday...have lowered maximum temperatures a bit. The models have been 
advertising flat ridging across the area Wednesday through Friday...with weak 
offshore grads each night...and weak onshore grads during the 
days...and temperatures at least a few degrees above normal across the 
area. The latest model runs now show a weak upper trough off the 
coast...which could inhibit warming and the reduction of stratus... 
at least in coastal areas. 


&& 


Aviation... 


30/1200z 


1400 foot inversion in place over klax but middle and high cloud layers 
have disrupted low cloud formation over l.A. County. Marine layer 
tapers down to 600 feet over the central coast where LIFR ceilings and 
visible will dominate through middle morning. Scattered thunderstorms and rain over the mountains 
this afternoon will pose problems for in and outgoing air traffic. 


Lax...low clouds are 15 miles west of the Airport. There is a 40 
percent chance that these clouds will arrive at the Airport by 14z 
and last until 18z. Ceiling reformation tonight is likely but the time of 
ceiling arrival is quite uncertain. 


Bur...good confidence in VFR taf. 


&& 


Lox watches/warnings/advisories... 
Flood Watch (see laxffalox). 
Gale Warning (see laxmwwlox). 


&& 


$$ 


Public...Bruno/meier 
aviation...rorke 


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