657 
fxus66 klox 210254 
afdlox 


Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
800 PM PDT Sat Mar 20 2010 


Synopsis... 


Dry weather will continue through next week with warmer than normal 
temperatures expected over the weekend...then gradual cooling 
through early next week. Coastal sections will remain cool through 
the period due to a persistent marine layer presence. 


&& 


Short term (tonight-tue)...weak upper level high pressure combined 
with weak offshore flow near the surface to bring another warm day 
across inland areas...with many locations topping the 80 degree mark. 
A shallow but strong marine inversion kept immediate coastal areas 
cooler with some persistent fog issues. The combination of weak offshore 
pressure gradients (lax-dagget currently at -0.9 mb) and a shallow but 
strong marine inversion will continue to make immediate coastal areas 
vulnerable to dense fog tonight. Current satellite imagery showing 
areas of low clouds and fog affecting the immediate portions of the 
central coast and la County coast...but do expect low clouds and fog to 
fill in across portions of the Ventura and sba South Coast overnight. Later 
shifts may need to issue a dense fog advisory if areal extent begins to 
increase overnight. 


With pressure gradients expecting to trend onshore Sunday afternoon 
and slight cooling in the boundary layer temperatures...look for a few 
degrees of cooling in most coastal and valley locations on Sunday... 
with this cooling trend to continue into Monday. 


*** From previous discussion *** 


The models have been having some trouble handling the upper low that 
comes through the southern branch of the jet and into Southern California and northern 
mex early next week, though today's runs, including the ECMWF, were 
in really good agreement. All show the low moving into northern Baja California 
Tuesday morning. Although it's too far south to generate any precipitation 
over our area, models do indicate some middle level moisture and 
instability near the low center and I expect there will be some 
showers and possibly some convection as it moves onshore in Mexico. 
It's very unlikely this low will drift any further north as there 
will be a system dropping south through the Great Basin late Monday 
which will prevent any such northward incursion. The Great Basin 
system will bring some cooler air aloft with it on Tuesday, likely 
deepening the marine layer over la/Ventura counties and cooling 
daytime temperatures. Increasing north/northeast flow across sba/slow 
counties will likely push the marine layer offshore Tuesday with 
slightly warmer highs. 


Long term (wed-sat)...there will be a brief one day offshore surge 
on Wednesday following the passage of tuesday's trough. The combination of 
this and ridging aloft will result in a nice bump up in temperatures. 
Slightly cooler temperatures Thursday-Sat as gradients turn weakly onshore, but 
still a few degrees above normal. Marine layer clouds likely to remain 
near the coast through the period. 


&& 


Aviation...20/2345z. 


Erratic stratus pattern this afternoon with areas forming along the 
central coast and la/vtu County coastal areas. At this time...the 
low clouds and fog are confined to immediate coastal areas but expected 
to spread locally inland across the coastal plain overnight. With 
weak pressure gradients and low/strong inversion in place...could see 
areas of reduced visibilities 1-3sm...with isolated visibilities down to 1/4 mile. 
At this time...does not appear that marine layer will be sufficiently 
deep for stratus to reach valley areas. 


Klax...sct-bkn conditions expected during next few hours at klax... 
with more solid coverage expected tonight. Best estimate of ceiling 
height/visibilities would be 003-006 with 2-4sm...but slight chance of 
ceilings at or below 002 with vsybs at or below 1sm. Fairly confident that ceilings will 
lift by 17-18z Sunday. 


Kbur...it is very likely VFR conditions will persist. 


***Note*** 
the ASOS equipment at kbur...kvny...khhr...kcma...and koxr has a 
software error that may lead to incorrect cloud heights when there 
are two or more cloud layers present. Observations at kbur will be 
quality controlled 24 hours a day...observations at kvny will be 
quality controlled from 13z-07z...observations at koxr will be 
quality controlled from 15z-05z. Tafs for kvny and koxr will not be 
amended for ceilings during the time the observations are not monitored 
and there are two or more cloud layers present. 


&& 


Lox watches/warnings/advisories... 
none 


&& 


$$ 


Public...gomberg/Wofford 
aviation...gomberg 
synopsis...Sweet 


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