Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 211749

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
944 AM PST Tue Nov 21 2017

A strong ridge of high pressure aloft and weak offshore flow will
likely bring record heat to portions of Southwest California at
times through Thanksgiving Day. The ridge will slowly break down
heading into this weekend supporting a gradual cool down.
Additional cooling and locally gust northerly winds possible early
next week as a weakening cold front pushes through the region.



Main weather story over the next few days will be record heat
as a strengthening upper level ridge of high pressure over
Southwest California combines with offshore flow near the surface.
A strong 592 dm upper high is currently centered off central
Baja this morning with rising heights/thicknesses over Southwest
California. Meanwhile, LAX-Daggett gradient has peaked at -6 mb
this morning, which is stronger than models earlier advertised.
As a result of this slightly stronger offshore push, will see
some northeast winds gusting between 25 and 35 mph across the
mountains and valleys of LA/Ventura counties today, with isolated
gusts up to 40 mph across favored mountain areas. Lighter offshore
breezes could also surface across the Ventura county coastal
plain during the next few hours. Due to current temperature
trends, stronger offshore gradients, and significant boundary
layer temperature rises noted in the profiler/sounding data, have
nudged high temperatures up a few more degrees in some areas for
today in morning update. Official record highs that are
forecasted to be broken today include Burbank, Woodland Hills,
Lancaster, Paso Robles, and Sandberg. There will continue to be
some higher level clouds drifting over the area today, but should
have  minimal impact on high temperatures.

Even hotter temperatures still on track for Wednesday, when
widespread record heat is forecasted across the region. Many
coastal/valley areas expected to climb into the lower to mid
90s on Wednesday. Offshore winds gusting between 30 and 40 mph
expected on Wednesday morning across the mountains and valleys of
LA/Ventura counties.

Elevated fire danger exists for Southwest California much of
this week due to the combination of hot temperatures, low
humidities, offshore breezes, and very dry fuels. Brief critical
fire weather conditions will be possible today and Wednesday
across LA/Ventura counties when the offshore winds will be

*** From previous discussion ***

The upper high off Baja will strengthen a bit and lift northward
tonight and Wed. This will cause heights and thicknesses to rise
additionally across the forecast area. Offshore gradients will
increase a bit more by Wed morning. Expect areas of gusty northeast
winds across the mtns and valleys of L.A./VTU Counties, the VTU
County coastal plain, and coastal sections of L.A. County below
passes and canyons from Malibu to the Hollywood Hills, with winds
peaking Wed morning. At this point, it appears that winds, though
probably stronger than today, will remain just below advisory levels.
It will be a warm night in windy areas and in the foothills of
L.A./VTU Counties, with temperatures likely remaining in the 70s
through the night. There will be additional warming at 950 mb on
Wed, especially near the coast of L.A./VTU Counties. Max temps
Wed should be up several degrees in coastal areas, with a few
more degrees of warming expected in the valleys. Expect some
record high temperatures coastal and valley areas on Wed, with
highs possibly reaching 95 degrees in a couple of locations, more
than 20 degrees above normal for late November.

The upper high will move little Wed night and Thu morning, then
perhaps begin to be nudged southward Thu afternoon as a large
trough moves into the eastern Pacific. However, low level
gradients will still be almost 4 mb offshore between KLAX and
KDAG in the morning, then just become nearly neutral in the
afternoon. Temps at 950 mb will change little. There may be some
locally gusty northeast winds Wed night/Thu morning, but winds
will be weaker and less widespread. It will be another very warm
night Wed night, then expect another very warm to hot day on Thu.
There may be a few degrees of cooling Thu, mainly near the coast.
Max temps should still reach or exceed 90 degrees on Thu in the
valleys, and possibly across interior sections of the coastal
plain. The highest temperature ever recorded in Downtown Los
Angeles on Thanksgiving Day (on which the date varies from year to
year) was 90 degrees on November 26th, 1903.


The EC and GFS are in good agreement showing the upper high
weakening some on Fri. At the same time, offshore gradients will
weaken, then turn onshore Fri afternoon. There should be several
degrees of cooling on Fri, especially west of the mountains, and
especially across the coastal plain. Still, temps should be at
least 10 degrees above normal in many areas.

The upper high will be nudged slowly eastward over the weekend as
a trough approaches the West Coast, and heights and thicknesses
will gradually fall. Onshore flow will increase each day. This
will result in a gradual cooling trend over through the weekend,
through max temps will probably still be above normal through
Sunday. The trough will move into the West Coast Sun night and
Mon, and while any rain will likely to stay to the north of the
region, there will be more significant cooling, with temps
possible dropping to below normal levels.



At 1712Z, there was a surface-based inversion at KLAX. The top of
the inversion was 2000 feet with a temperature of 25 degrees

High confidence in 18Z TAFs as weak offshore flow will keep all
sites VFR through Wed morning.

KLAX...High confidence in the 18Z TAF with VFR conditions expected
through Wed afternoon.

KBUR...High confidence in the 18Z TAF with VFR conditions expected
through Wed morning.


.MARINE...21/800 AM...

For the Outer Waters, good confidence in current forecast. Winds
and seas are expected to remain below Small Craft Advisory (SCA)
levels through Wednesday. On Thursday/Friday, there is a 50%
chance of SCA level winds across PZZ670/673. Winds will diminish
on Saturday.

For the Inner Waters, good confidence in current forecast. For the
waters north of Point Sal, winds and seas are expected to remain
below SCA levels through Saturday although there is a 20% chance
of SCA level winds Thursday afternoon/evening. For the waters
south of Point Conception, winds and seas are expected to remain
below SCA levels through Saturday.




Hot and very dry conditions are expected Thursday, with warm and
dry conditions Wednesday night. There will be gusty winds at times
across portions of Los Angeles and Ventura Counties. There will
likely be elevated fire danger across portions of Los Angeles and
Ventura Counties during this time.



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