Freeze Warning 11, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1057 AM PST Tue Dec 5 2017

.SYNOPSIS...
Strong offshore winds have developed across much of Ventura and
Los Angeles Counties and will continue through Friday. Winds will
be strongest through this afternoon and again late Wednesday night
through Thursday with damaging wind gusts expected in some areas.

&&

.SHORT TERM...(TDY-THU)

Strong Santa Anas today as winds developed more or less as
expected. We're experiencing a peak in the winds this morning
before gradients and upper support drop off slightly this
afternoon through Wednesday. Winds will still be gusty but likely
drop below warning levels for all but the higher peaks and
mountains and advisories will replace the warnings in those areas
and continue through Wednesday. All in all forecast in good shape
and not expecting any major changes except overnight low
temperatures may need some adjustment in some areas to account
for the wind factor which definitely kept minimums from falling as
much as expected.

***From previous discussion***

Strong offshore gradients will continue across L.A. and VTU
Counties tonight and Wed as strong surface high pressure settles
into the Great Basin. A strong upper level high just off the Pac
NW will move slowly eastward through Wed. Winds aloft and
subsidence through the atmosphere will decrease some across the
area tonight through Wed. This will cause the winds to abate a
bit, but still expect advisory level winds to continue in many
coastal and valley areas of L.A. and VTU Counties through Wed
evening. Wind Advisories will likely replace the High Wind
Warnings in the valleys and coastal areas once they expire. In the
mtns of L.A. and VTU Counties, damaging gusts to 60 mph will
likely continue through Wed.

Max temps will be up a few degrees west of the mountains today,
but little change or even some cooling is expected in the
mountains and deserts. Additional warming is expected west of the
mountains on Wednesday, with highs reaching 80 degrees in the
warmest locations on the coastal plain and in the lower valleys.
Some warming is also expected in the mtns and deserts.

Tonight and Wed night will be very cold in wind sheltered
locations, especially across SBA and SLO Counties and in the Ojai
Valley. Freezes or hard freezes are likely across much of
interior SLO and SBA Counties. Freezes are possible in the Ojai
Valley, and on the Central Coast, and possibly across the
south coast of SBA County.

A strong vort will drop southward through Utah and eastern Nevada
Wed night and early Thu. This will cause upper level north to
northeast winds to strengthen once again across the region, with
another area of strong subsidence spreading into the area. In
addition, the WRF shows offshore surface pressure gradients
increasing once again, to an incredibly steep 11 mb between KLAX
and KDAG! Expect winds to increase once again Wed night, then
peak Thu morning into early Thu afternoon. Wind gusts may again
reach 70 to 80 mph in the mountains of L.A. and VTU Counties, and
50 to 60 mph in the valleys and in coastal sections of VTU
Counties. High wind warnings remain in effect for the mtns of L.A.
and VTU Counties through Thu afternoon, and High Wind Watches may
be needed for the valleys and the VTU County coast. With rising
heights and thicknesses, expect some warming in most areas on Thu.
While critical fire weather conditions are expected across much
of L.A. and VTU Counties through Thu, there is a chance that Thu
will have the most extreme conditions, due to a warmer and even
drier air mass and similar wind conditions.

.LONG TERM...(FRI-MON)

The strong elongated upper high will linger across the West Coast
states through Sat. Low level gradients will remain offshore, and
although they will be a bit weaker, and upper level support will
weaken as well, gusty winds will continue to affect portions of
L.A. and VTU Counties, probably at advisory levels, at least
through Fri. High fire danger will likely continue, and Red Flag
Warnings will probably have to be extended through at least Fri.
Max temps will likely rise a bit in most areas on Fri, then change
little on Sat.

A very weak upper low will develop off the coast of southwestern
California Sat night and Sunday, then drift eastward into northern
Baja CA on Mon. Offshore gradients will weaken a bit more on
Sunday, but then will increase again on Monday. Do not expect any
major changes in max temps Sun or Mon, with daytime temps well
above normal, and warmest locations likely having highs around or
just above 80 degrees.

&&

.AVIATION...05/1800z.

At 1808z at KLAX...there was no marine layer.

Overall... Moderate to high confidence in the current TAFs. There
will be strong and gusty Santa Ana winds across many TAF sites
south of Point Conception throughout the forecast period with the
strongest winds lessening in the late afternoon and evening hours.
Only moderate confidence in the timing and strength of the winds
for KSMO, KLAX, and KLGB as the stronger winds may remain elevated
but there will at least be wind shear with height at these sites.
Many locations will experience turbulence and low level wind shear
due to very strong and gusty Santa Ana winds. Brush fires in the
area will also cause some obscuration of visibility due to
widespread swaths of smoke.

KLAX... Moderate to high confidence in the current TAF. There
will be strong and gusty Santa Ana winds across the terminal
vicinity in the morning with winds lessening in the late
afternoon and evening hours. Otherwise VFR conditions will
prevail. There is a forty percent chance of east winds to ten
knots 15z-21z Wed.

KBUR... Moderate to high confidence in the current TAF. There
will be strong and gusty Santa Ana winds across the terminal
vicinity in the morning with winds lessening in the late
afternoon and evening hours. Otherwise VFR conditions will
prevail. There is a 30 percent chance of obscuration due to smoke.

&&

.MARINE...05/900 AM.

Gusty northeast winds and choppy seas will continue Small Craft
Advisory (SCA) conditions over the southern portion of the outer
waters into midday.

South of Point Conception, northeast Gale Force winds with gusts
to 40 knots will continue through this afternoon in the near shore
waters from Ventura to Santa Monica. There is a 20 percent chance
of SCA level gusts over near shore portions of the Central Coast
waters during this time.

Northeast winds gusting to 30 knots will likely affect the San
Pedro Channel out to Catalina Island during this time with short-
period hazardous seas of 3 to 6 feet. The wind driven seas will
cause boating hazards for east-facing harbors and inlets, such as
Avalon Harbor and other offshore islands.

The offshore winds will begin to diminish in speed this afternoon
and fall below SCA levels overnight. A second burst of offshore
winds will bring another round of SCA or gale winds and seas
across the inner waters south of Point Conception Wednesday night
into Thursday and possibly continuing into Friday morning.

&&

.FIRE WEATHER...05/445 AM...

Overall, everything is still on track with current fire weather
forecast. Widespread critical fire weather conditions are expected
across Ventura and Los Angeles counties through Thursday.
Winds will peak in strength this morning (gusts between 60 and
80 mph). The winds will diminish in strength on Wednesday, but
will increase again Wednesday night and Thursday with some warning
level gusts likely yet again. Relative humidity will drop into the
single digits and low teens each day with poor overnight recovery.
With fuels still extremely dry, Red Flag Warnings will remain in
place for Ventura and Los Angeles counties through Thursday
afternoon.

For Friday through the weekend, the northeast winds will diminish
in strength, but will remain offshore. At upper levels, high
pressure will develop along the West Coast. So, warm and dry
conditions will continue through the weekend. Critical fire
weather conditions may persist through the weekend and the current
Red Flag Warnings may need to be extended.

If fire ignitions occur this week, there will be the potential
for very rapid fire spread, long range spotting, and extreme fire
behavior. Long range computer models are showing the potential for
the Santa Ana winds persisting into Friday or Saturday, which may
require the extension of the Red Flag Warning. Everyone needs to
exercise extreme caution when handling any potential fire ignition
sources...such as campfires, cigarettes, welding and brush
clearing equipment.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Freeze Watch in effect from late tonight through Wednesday
      morning for zones 34>36-38-44. (See LAXNPWLOX).
     High Wind Warning in effect until 4 PM PST this afternoon for
      zones 40-44-45-88-547. (See LAXNPWLOX).
     Wind Advisory in effect until 4 PM PST this afternoon for
      zones 41-87. (See LAXNPWLOX).
     High Wind Warning in effect until 4 PM PST Thursday for zones
      46-53-54. (See LAXNPWLOX).
     Red Flag Warning in effect until 6 PM PST Thursday for zones
      240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Gale Warning in effect until 3 PM PST this afternoon for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PST this afternoon
      for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
Damaging Santa Ana winds are expected across portions of Ventura
and Los Angeles Counties Thursday, with gusty winds continuing
on Friday. Critical fire conditions are expected through at least
Thursday, and likely into Friday due to winds and extremely low
relative humidites.

&&

PUBLIC...MW/DB
AVIATION...Sweet
MARINE...Sweet
FIRE...Thompson/DB
SYNOPSIS...JLL

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