Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 220413
AFDLOX

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

.SYNOPSIS...
Record to near record temperatures are forecast into Friday due
to the combination of an unseasonably strong upper ridge and gusty
offshore winds persist over the region. An upper level trough
will approach by Sunday for increasing clouds and cooler
temperatures. A surface high pressure is expected to build into
the Great Basin by late Monday and into early Wednesday allowing
for gusty offshore winds.

&&

.SHORT TERM...(TUE-FRI)

No changes to the forecast expected this evening. Forecast is in
good shape. Latest 00z models are in, and continue to show record
breaking heat potential for Wed and Thanksgiving. Tomorrow should
be the hottest day with only a degree or two of cooling for the
valleys and immediate coastal expected for Thanksgiving. The
seabreeze should pick up earlier along the coast for Thanksgiving,
but still remain very warm before the seabreeze kicks in.

Latest fog product imagery indicated most of the high clouds
moving up and around the strong upper ridge keeping the high
clouds to the north and east of the forecast area this evening.
The upper level ridge has strengthened over the region today. Weak
to locally moderate offshore flow allowed for some significant
heating today as expected. In fact Downtown L.A. was 15 degrees
warmer than yesterday at 88 degrees. Most coast and coastal
valleys were up 8 to 20 degrees today, while interior valleys,
mountains and the Antelope Valley rose 4 to 10 degrees for the
most part. There were 5 official records broken today including
Burbank, Woodland Hills, Sandberg, Santa Maria and Paso Robles.
Warmest areas reached the lower 90s including San Luis Obispo at
90 degrees, Ojai was the warmest location at 94 degrees and
plenty of lower 90s across the L.A. and Ventura County coastal
valleys.

As the upper ridge continues to strengthen over the area with
continued offshore flow and sub advisory wind gusts for Wednesday,
temps will continue to climb. Should double the amount of records
that were broken today including Downtown L.A where a 93 is being
forecast. Most of L.A. and VTU counties will see temperatures
rise an additional 5 to 10 degrees on Wed. A slight cooling trend
is expected across the Central Coast due to the seabreeze kicking
in a bit earlier tomorrow. Although some locations were and will
continue to be around 20 degrees warmer than normal for this time
of year over the next few days, not expecting oppressive heat
overnight due to less daylight, lower sun angle and dry conditions
which help in the cooling process. Lows will remain in the mid
60s to lower 70s across some of the wind prone areas overnight.

***From Previous Discussion***

Main weather story over the next few days will be record heat,
which is expected to peak on Wednesday. This heat wave being
caused by a strong upper level ridge building over Southwest
California today, peaking in strength on Wednesday when heights
are expected to reach 593 dm.

On Wednesday, offshore winds are expected to be slightly stronger
and more widespread across the region, with gusts ranging between
30 and 40 mph across wind favored valleys/mountains of LA/Ventura
counties, falling just below advisory levels. LAX-Daggett gradient
expected to climb to around -6 mb again Wednesday morning. Offshore
breezes are also expected to briefly surface across the Ventura
County coastal plain and Malibu to Hollywood Hills on Wednesday
morning. As a result, looking for widespread record breaking heat
on Wednesday, including coastal areas. Highs across most coastal
and valley areas expected to range from the upper 80s to mid 90s
on Wednesday. In addition, very warm overnight lows (in the 70s to
around 80) are expected in the foothills and wind prone areas. As
a result, there is the potential for some moderate heat impacts
on Wednesday, especially in the foothills and Santa Monica
mountains where there will be little relief in the heat through
the overnight hours.

Upper level ridge and offshore gradients are expected to weaken
slightly on Thanksgiving Day, leading to 2 to 3 degrees of cooling
for most coastal/valley areas. However, it should be noted that
despite this slight cooling, temperatures will still reach record
levels on Thanksgiving Day, including many temperatures into the
lower to mid 90s in the valleys. Also of note is the forecasted
high of 90 degrees for Downtown Los Angeles on Thanksgiving Day
which would tie an all-time high temperature for the holiday. The
highest Thanksgiving high temperature for downtown Los Angeles
was set on November 26th, 1903.

The combination of hot temperatures, low humidities, and very dry
fuels will lead to elevated fire danger through the remainder of
the week. Brief critical fire weather conditions will persist this
afternoon through Wednesday when the offshore winds will be
strongest across Los Angeles and Ventura counties.

.LONG TERM...(SAT-TUE)

The EC and GFS are in good agreement that the upper level ridge
will continue to gradually shift eastward through the weekend
leading to a continued cooling trend with increasing higher
level clouds. A weak cold front is expected to bring precipitation
to Northern and Central California this weekend. The latest
operational GFS/ECMWF models and GFS ensemble members showing
the trailing edge of this system could bring a slight chance of
showers to SLO county sometime between Sunday and Monday morning.
As the weak trough moves through the area, looking for
temperatures to return to near normal levels with highs in the
lower to mid 70s.

From Monday night into Tuesday, the upper level trough is
expected to dig southeastward into the four corners area,
with a strong 1036 mb surface high building into the Great
Basin. There is the potential for strong northerly winds
across the mountains and SBA south coast on Monday night,
followed by the potential for a strong Santa Ana wind event
on Tuesday. While it is still very early, the GFS and ECMWF
models are in fairly good agreement on the upper level pattern
and potential for a strong north-northeast offshore pressure
gradient in the Monday night-Tuesday time period. The offshore
flow will likely persist into Wednesday, with the potential
for moderate intensity.

&&

.AVIATION...22/0030Z...

At 2356Z, there was a surface-based inversion at KLAX. The top of
the inversion was around 1400 feet with a temperature of 28
degrees Celsius.

High confidence in 00Z TAFs as weak offshore flow will keep all
sites VFR through Wed morning.

KLAX...High confidence in the 00Z TAF with VFR conditions
expected through Wed evening.

KBUR...High confidence in the 00Z TAF with VFR conditions
expected through Wed afternoon.

&&

.MARINE...21/800 PM...

For the Outer Waters, good confidence in current forecast. Winds
and seas are expected to remain below Small Craft Advisory (SCA)
levels through Wednesday. For Thursday through Friday there is a
50% chance of SCA level winds for PZZ670, and a 50% chance of SCA
level winds for for PZZ673 Thu night. Otherwise conditions across
the outer waters will remain sub-SCA level through Saturday, with
another chance of SCA winds on Sunday.

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 Sunday, 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 Sunday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(FRI-TUE)
Hot and very dry conditions are expected Thanksgiving Day which
will continue to bring elevated fire danger. There is the
potential for greater fire weather impacts Monday night into
Tuesday. On Monday night, there will be the potential for
strong northerly winds and lowering humidities, followed
by the potential for a strong Santa Ana wind event and even
lower humidities on Tuesday.

&&

$$

PUBLIC...Kaplan/Gomberg
AVIATION...Kaplan
MARINE...Smith
SYNOPSIS...STu

weather.gov/losangeles


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