000
fxus66 klox 070542 aaa
afdlox

southwest california area forecast discussion...updated
national weather service los angeles/oxnard ca
1040 pm pdt mon sep 6 2010

updated aviation section

.synopsis...

temperatures will cool to well below seasonal normals through friday
as a deep trough pushes through the area. night through morning low
clouds and fog will affect coastal and valley areas as well...
likely reaching the coastal slopes and producing drizzle by
wednesday. as the upper level trough pushes east over the weekend...
the marine layer will shrink some and temperatures will rise.

&&

.short term (tonight-thu)
temperatures were cooler for the most part across the forecast area
today except little change across the interior portions of slo
county and only a subtle warm up across the santa barbara central
coast from local offshore winds this morning. otherwise much of la
and ventura interior areas were down 5 to 10 degrees today.

as the trough off the west coast continues to dig farther
south...the marine layer will continue to deepen as the inversion
weakens with added cooling across the region. latest amdar sounding
near klax was around 2000 ft. onshore trends will increase over the
next couple of days as well. this will bring a wider area of low
cloud and patchy fog coverage across all la/vtu sba county
valleys...including the santa clarita valley overnight. will likely
update coastal zones for la/vtu counties to keep low clouds near the
beaches through at least mid afternoon hours tuesday.

as the trough continues to deepen...h5 heights and thickness lvls
will continue to fall bringing additional cooling the region
tomorrow with warmest temps in the valleys in the lower to mid
80s...while the antelope valley reaches the lower 90s.

by wednesday...the upper trough becomes a closed low over nrn cal
and oregon. a positive tilted deep trough will move across the
region bringing well below normal high temps to the entire cwa with
the definite possibility of some local drizzle to the region as the
marine layer should be around 3000 ft.  temps should bottom out on
wednesday into thu with highs only reaching the mid 60s to mid 70s
across coast and valleys with the antelope valley only expected to
reach the lower 80s...around 10 degrees below normal. as the trough
passes through the area on thursday...low clouds should scour out
across the central coast and possibly across areas s of point
conception. however models continue to indicate a very deep marine
layer influence...especially across la/vtu counties...so will lean
with mostly cloudy skies in the morning with drizzle possible across
the la/vtu c0unties...especially in the foothills. again...the one
caveat for thursday will be the possibility of the colder air behind
the trough axis helping to mix out the low clouds. temps should be
very similar on thursday with maybe a degree or two of warming
across slo county.

***from previous discussion***

.long term (fri-mon)...12z extended models are not in great synoptic
agreement. gfs develops a rather zonal pattern across the area
through the period while the ecmwf/gem indicate a bit more amplified
pattern with a couple weak troughs moving across the west coast.

given the lack of agreement...will not change forecast thinking too
much through the period. it does appear h5 heights will gradually
increase...so will expect the marine layer stratus to be less
extensive each night. as for temps...will expect a gradual warming
trend through the weekend...but still remaining below seasonal
norms.

&&

.aviation...07/0535z.
wdsprd mvfr conds at all cstl and valley sites overnight/tue
morning...with lcl ifr and possibly lifr conds on the central coast.
clearing will likely be slow and incomplete on tue near the coast.

klax...moderate confidence in taf. there is a 20 to 30 percent
chance that vfr conds will be the predominant conds between 19z tue
and 02z wed.

kbur...moderate to high confidence in taf. there is a 10 to 20
percent chance that cigs will linger through 22z.


&&

.lox watches/warnings/advisories...
none

&&

$$

public...kaplan/thompson
aviation...db
synopsis...meier

www.weather.gov/losangeles

NWS LOX Office Area Forecast Discussion