000 
fxus66 klox 251626 
afdlox 


Area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
926 am PDT Wed Apr 25 2018 


Synopsis...25/316 am. 


A trough of low pressure will approach the West Coast through 
Friday before settling over the region through early next week. 
This will result in a gradual cooling trend with increasing night 
to morning low clouds through Friday. Near normal temperatures 
will continue into early next week. 


&& 


Short term (tdy-fri)...25/925 am. 


Low clouds have already exited the la coastal areas except for 
Palos verdes and fog is rapidly dissipating north of Paso Robles. 
Low clouds and patchy fog are rather entrenched along the central 
coast and the Ventura County coast so these areas will be slowest 
to burn off today. Onshore pressure gradients are rather Standard 
for this type of pattern and expected to peak at 7mb this 
afternoon from lax-dag. Locally gusty southwest winds to 45 mph 
will be likely in the foothills and western areas of the Antelope 
Valley today, but not enough to maintain Wind Advisory criteria so 
have canceled that for today. Gradients shoot up over 9mb on 
Thursday and MOS supports sustained winds of 20kt in Lancaster 
tomorrow which is more capable of reaching advisory levels then. 


Remainder of the forecast remains on-track with warm inland 
temperatures and cool coastal temperatures today. 


***From previous discussion*** 


Latest satellite imagery shows low clouds behaving just about as 
expected for once, with clouds socked into all coastal areas and 
now working into lower valleys. Patchy fog is likely across many 
valley locations this morning. An upper level low pressure system 
is also visible on satellite, about 1000 miles west of the region. 
This system is expected to meander well off the coast today 
before pushing east into the norcal coast Friday. Increasing 
onshore flow and night to morning clouds is expected through early 
Friday as a result of the approaching system. However, cooler air 
aloft with the system will likely weaken the marine layer 
inversion enough to wipe out low clouds north of Point Conception 
Friday night. The increasing marine influence combined with 500 mb 
heights lowering from around 580 dm today to around 574 dm Friday 
will support a continued gradual cooling trend away from the 
coast. Patchy drizzle is possible (though left out of the forecast 
for now) across eastern la County due to the deepening marine 
layer and a vort Max moving overhead early Friday. An advisory 
level sundowner is likely for the sba South Coast from Goleta to 
Gaviota Thursday evening, with a more widespread and possibly 
stronger sundowner expected Friday evening and night (with GFS 
indicating both sba- smx and sba- smx around -5). Advisory level 
northwest winds are also possible Friday evening and night in the 
mountains near the I-5 corridor and western Antelope Valley. 


Long term (sat-tue)...25/357 am. 


Above average confidence in the forecast exists through this 
weekend with below average confidence for early next week. 


Northerly and likely advisory level winds may continue at times 
through early next week for wind prone mountain and foothill 
locations. Advisory level winds may surface in wind prone valleys 
at times during this period, especially for Santa Clarita and San 
Fernando valleys. The gusty offshore flow and cold air advection 
will help to vastly reduce if not completely eliminate night to 
morning low clouds across the region. However, the current 
forecast hangs onto some low clouds for la County with the 
potential for an eddy which would help combat the offshore flow. 
A second piece of upper level energy may help to reinforce the 
trough of low pressure overhead early next week. This will keep 
near to below normal temperatures across the region during this 
time with gusty winds possible, especially across the mountains. 
There is also a non- zero change for rain sometime early next 
week, however given the time of year and continued inconsistency 
in model runs, have kept pops below mentionable levels for now. 


&& 


Aviation...25/0704z. 


At 0230z at klax, the marine layer was near 1000 feet deep. The 
top of the inversion was near 2300 feet with a temperature around 
19 c. 


Moderate confidence in tafs. There is a 30 percent chc that LIFR 
cigs may be IFR and vice versa. VFR transitions could be off by 
+/- 90 minutes. Good confidence in tafs 20z-02z. 


Klax...moderate confidence in taf. There is a 20 percent chc of 
LIFR cigs 11z-15z. VFR transition may be as late as 20z. 


Kbur...moderate confidence in taf from 10z-17z, otherwise very 
good confidence in taf. There is a 30 percent chance of LIFR cigs 
12z-16z. There is a 20 percent chc of no cigs. 


&& 


Marine...25/258 am. 


High confidence in winds and seas remaining below Small Craft 
Advisory levels across the waters through Wednesday. Winds will 
likely increase Thursday afternoon through Saturday with at least 
strong advisory level winds and possible gale force gusts along 
with building short period seas. 


&& 


Lox watches/warnings/advisories... 
California...none. 
Pz...none. 


&& 


Hazard potential outlook (fri-tue). 


No significant hazards expected. 


&& 


$$ 


Public...boldt/Munroe 
aviation...rorke 



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