Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 210016

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
416 PM PST Mon Nov 20 2017

A ridge of high pressure building into the region and weak
offshore flow will likely bring record heat to portions of
southwest California sometime Tuesday Through Thanksgiving day.
The ridge will gradually break down as a trough of low pressure
approaches the West Coast, supporting a cooling trend heading into
this weekend.



Plenty of high level clouds continued to move into the forecast
area this afternoon. Filtered sunshine thru the high clouds will
prevail thru sunset over much of the area. Fairly decent northerly
gradients were noted early this afternoon (e.g., at 21Z -2.7 mb
LAX- BFL, and -2.9 mb SBA-BFL) was supporting locally gusty NW to
N winds over the Santa Ynez Mtns and L.A. County mtns. The winds
are expected to continue thru the afternoon, and may expand some
over these areas, with gusty NW winds possible along the I-5
corridor by early evening. Temps this afternoon will be several
degrees above normal, with highs in the warmest vlys and inland
coastal areas expected to top out in the mid 70s to low 80s.

Generally flat and dirty upper level ridging over the forecast area
this afternoon, with 500 mb heights around 582-584 dm, will
gradually build tonight thru Wed. By Wed afternoon, 500 mb heights
will increase to 590-592 dm across the region. The upper ridge will
continue Wed night and weaken slightly Thanksgiving Day, with 500
mb heights lowering to 587 to 590 dm.

The mid and hi level moisture over the region will linger into
tonight then clear out by early Tue for sunny days and clear
nights Tue thru Thanksgiving Day.

Northerly gradients will increase some thru tonight which will
support gusty N canyon winds for the SBA County S coast and mtns,
with local gusts to advisory levels possible. Gusty NW winds can
also be expected in the L.A./VTU mtns along the I-5 corridor this
evening, then transition to N to NE and expand S into the favored
foothills and vlys of VTU/L.A. Counties later tonight into Tue
morning. Locally gusty NE winds will be possible over these areas of
VTU/L.A. Counties again Tue night into Wed morning. Otherwise, there
will generally be weak offshore low level flow over swrn CA tonight
thru Wed, especially during the night and morning hours. Weak
offshore flow will persist Wed night into Thanksgiving day,
especially over VTU/L.A. Counties.

The rising 500 mb heights, warming boundary layer and 950 mb temps,
and offshore flow, will all help to bring much warmer than normal
temps to the forecast area Tue thru Thanksgiving day. Near record to
record high temps will be possible for several climate stations
during the period. Temps should be warmest on Wed as highs should be
generally 15 to 20 deg above normal for many areas. Temps in the
warmest vlys and inland coastal areas should reach the mid 80s to
low 90s on Tue, low to mid 90s on Wed, and upper 80s to low 90s on
Thanksgiving Day. Even overnight temps should be very mild in the
breezy foothill and lower mtns Tue night and Wed night where lows in
the low to mid 70s will be possible.

Incidentally, the highest temperature ever recorded at downtown Los
Angeles on Thanksgiving Day (on which the date varies from year to
year) was 90 degrees on November 26th, 1903. This record has the
potential to be tied or broken this upcoming Thanksgiving Day as the
forecast high is 90 degrees, but there is the possibility of temps
reaching 91 or even 92 degrees. (However, the actual record high for
November 23rd is 91 degrees set in 1933, so the daily record may not
be set.) The rest of the top 5 warmest Thanksgiving Days at downtown
L.A. include 89 degrees on Nov 27, 2014; 88 degrees on Nov 24, 1977;
and 87 degrees on both Nov 23, 1939 and Nov 24, 1932. Records for
downtown Los Angeles go back to 1877.


The EC and GFS are in generally good agreement over the e PAC into
the western U.S. Fri thru Mon, altho by Mon the GFS has a stronger
upper trof over the W coast than the EC. Went with a general blend
of the two models with the most uncertainty in the forecast for Mon.

The upper high will be slightly weaker but persist over srn CA for
Fri, then gradually weaken and move E of the area Sat thru Sun. A
broad upper level trof is forecast to move into the E pac to the W
coast for Mon, along with a surface cold front. The front should
remain N of SLO County Sun night and Mon, altho the EC does bring in
some light rain to that area by afternoon. Went with ghost POPs for
Sun night into Mon over SLO County (less than 15 percent). Some
increasing cloud cover ahead of the upper trof should begin as soon
as Sun then continue into Mon, especially for northern areas.

Temps are forecast to be significantly above normal on Fri, then
gradually cool but remain several degrees above normal for many
areas for Sat and Sun, then highs will fall to near normal to
slightly above normal for Mon. Highs in the warmest vlys and inland
coastal areas should be in the mid 80s to near 90 on Fri, low to mid
80s on Sat, upper 70s to around 80 on Sun, and generally in the 70s
on Mon.



At 2330Z, Around KLAX, there was a marine layer around 400 feet
deep with an inversion top of 2100 feet at 22 degrees Celsius.

High confidence in 00z TAFs over next 24 hours. Not anticipating
any stratus.

KLAX...high confidence in 00Z TAF.

KBUR...high confidence in 00Z TAF.


.MARINE...20/200 PM.

For the Outer Waters, moderate confidence in current forecast.
A SCA has been issued for zones 673 and 676, although the winds
are only expected to gust to about 25 knots through 05z this
evening. Winds will stay below SCA speeds Tuesday and Wednesday.
For Thursday and Friday, SCA level winds are likely.

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 Friday. For the waters south of Point
Conception, winds and seas are expected to remain below SCA levels
through Friday.


PZ...Small Craft Advisory in effect until 9 PM PST this evening
      for zones 673-676. (See LAXMWWLOX).


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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