Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 211230

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

Strong upper level high pressure and offshore flow will bring very
warm and dry weather to the area through Thanksgiving, with near
record temperatures possible. The high will weaken Friday through
the weekend and onshore flow will return. This will result in a
cooling trend, with temperatures back to normal levels by the
beginning of next week.



A strong 592 dm upper high was located off of central Baja CA
early this morning with an amplifying ridge extending into the
forecast area. There was still a good deal of high clouds
streaming into the region this morning. This cloud shield should
translate northward out of the region as the upper ridge continues
to amplify, but probably not until later today or tonight. There
should be enough clouds to justify partly cloudy wording in the
forecast for today. The pressure gradient between KLAX and KDAG
has trended offshore during the past 24 hours, and was now almost
5 mb offshore. Some gusty winds were occurring in the mountains of
L.A./VTU Counties early this morning. Expect winds to increase
and become more widespread, then spread into the L.A./VTU County
valleys and possibly coastal areas after sunrise. With marginal
gradients and limited upper support, expect winds to remain below
advisory levels for the most part today, with isolated advisory
level gusts in the normally wind prone locations.

The main story should be the sizable jump in temps today, as
heights and thicknesses rise, and 950 mb temps jump several
degrees. Max temps in some of the warmer locations in the valleys
and possibly across interior sections of the coastal plain should
be around 90 degrees today. If the high cloud shield remains as
thick as it currently is, max temps may end up a few degrees shy
of their potential.

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 1000Z, there was a surface-based inversion at KLAX. The top of
the inversion was 3400 feet with a temperature of 21 degrees

Overall, high confidence in 12Z TAF package as weak offshore flow
will keep all sites VFR through the period.

KLAX...high confidence in 12Z TAF.

KBUR...high confidence in 12Z TAF.


.MARINE...21/100 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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