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afdlox 


Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
210 PM PDT Sat Jul 19 2008 


Short term (today-tue)...main forecast questions during this period 
have to do with the moisture intrusion from the southeast and it's 
impact on our marine layer. Marinel layer was solid this morning with a 
depth around 2000 feet. Although little change in the depth is 
expected the next couple days, coverage may be significantly altered 
depending on the extent and depth of middle and upper level moisture. 
Models indicate that moisture amount will decrease substantially 
from east to west across our cwa, with basically little or no 
subtropical influence north and west of Ventura County. Precipitable waters are 
quite a bit lower than what we had late last week and earlier this 
week and lifted indice's are marginal at best with the best instability over 
the eastern la County mountains have generally left probability of precipitation alone through Tue, 
except I did decrease probability of precipitation to 10 or lower over the sba County 
mountains as the threat there is really too low to mention in the 
zones, at least according to the 12z model runs. 


The impact on the marine layer and resulting daytime temperatures is the big 
unknown right now. The 12z NAM is going with highs mostly in the middle 
70s to middle 80s across the la basin Sunday with a solid marine 
influence at lower elevations, but if the marine layer there becomes 
disrupted tonight as moisture increases from the southeast than 
temperatures will likely be much closer to the much warmer GFS numbers. 
I've trended the forecast closer to the NAM, but not completely. 


Similar dilemma Monday and Tue, though even the NAM is indicating a 
warming trend for the coast and valleys. GFS really starts to shut 
down the moisture Tuesday as drier air from the west moves in and precipitable waters 
drop well below an inch. Confidence in this solution is not high 
enough to drop probability of precipitation from the mountains and deserts so will leave 
those going for the time being. 


Long term (wed-sat)...GFS and European model (ecmwf) both indicate high pressure 
over the southwestern United States building and expanding. This 
should lead to a warming trend across our area later this week and 
into the weekend. Left in convective probability of precipitation for Wednesday but if the 12z GFS 
is correct this threat should be over well before Wednesday. The GFS does 
show an increase in monsoonal moisture again Friday and Sat and we may 
need to consider adding mountain and desert probability of precipitation later on if this trend 
holds over the next few model runs. Depending on the depth and 
extent of the moisture the warming trend over inland areas may be 
somewhat diminished as cloud cover and higher humidities may put a 
cap on daytime highs. However in this situation any decrease in 
temperatures would likely be offset by the corresponding increase 
heat indices due to higher humidities. 


&& 


Aviation...19/1800z. 
Marine layer up to 022 this morning...with solid MVFR stratus deck 
over most of the coastal side of the mountains most sites should see 
clearing by 20z...but low confidence of clearing at immediate 
coastal sites like klax koxr and ksba. These sites should see a few 
observation of VFR between 20z and 02z...but stratus should surge in to stay 
earlier than last night. Middle level moisture will begin to stream in 
overnight...which will likely alter the stratus...but low confidence 
if it is enough to break it up. Should improve flight cats a bit 
from last night nonetheless. 


Klax...moderate confidence of MVFR ceilings through 20z...with low 
confidence for improvement between 20z and 02z. Stratus should surge 
back in early tonight...with an onset window between 23z and 04z. 


Kbur...moderate confidence in VFR by 20z...but haze may linger an hour 
or two later. VFR should prevail afterward through the evening. 
Stratus should then return initially at IFR...with an onset time 
between 06z and 12z. 


&& 


Lox watches/warnings/advisories... 
high rip current risk (see laxsrflox). 


&& 


$$ 


Public...Wofford 
aviation...kittell 


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