Southwestern California Discussion

 
000
FXUS66 KLOX 240428
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
828 PM PST Thu Nov 23 2017

.SYNOPSIS...
Record temperatures in the deserts with above normal temperatures
inland are forecast into Friday as a high and offshore winds weaken.
A low will approach by Sunday for increasing clouds and cooler
temperatures. A high should build into the Great Basin late Monday
into early Wednesday for gusty offshore winds and put temperatures
into a warming trend. Another low may move in by late Wednesday.

&&

.SHORT TERM...(THU-SUN)

Though it was a bit cooler in most areas today, it was another
very warm day across Southwestern CA, with daily records broken in
at Downtown Los Angeles, LAX, Long Beach Airport, UCLA, Woodland
Hills, Burbank Airport, Sandberg, Lancaster, Palmdale, Camarillo
and Paso Robles Airports, and here at the National Weather Service
Office in Oxnard. In addition, it was the hottest Thanksgiving
Day ever in Downtown Los Angeles, where the 92 degree high
eclipsed both the Thanksgiving Day record of 90 degrees set on
November 26, 1903, and the daily record for the 23rd of 91
degrees, set in 1933.

Skies were clear across the region this evening, except for a few
high thin clouds. Some low clouds were trying to form well off the
Central Coast, but with offshore gradients continuing, they will
remain off the coast. N-S gradients were strong enough across SBA
County to be causing some gusty northwest to north winds through
and below passes and canyons of the Santa Ynez Range and the
adjacent south coast, but winds will remain below advisory levels
tonight. Will update the forecast to increase winds tonight there.
Otherwise, the current forecast is in good shape.

*** from previous discussion ***

Strong high pressure, responsible for the hot and dry air mass in
place, will weaken and flatten through the weekend as a broad
trough over the Eastern Pacific Ocean slowly displaces the ridge.
Cooling, albeit slightly, will become more widespread on Friday
and Saturday, with better cooling spreading over the area on
Sunday and Monday.

The trough will approach the West Coast over the weekend with a
stronger cold front scheduled to push south into the area between
Sunday and Monday morning. Model solutions are offering up timing
differences with the arrival of the cold frontal boundary, but
good agreement exists for the possibility of precipitation, mainly
north of Point Conception. Shower activity cannot be ruled out
south of Point Conception at this point as model solutions do
bring some moisture and instability south, but the question that
lingers is "How much?"

PoPs have been increased substantially for areas north of Point
Conception as both ECMWF and GFS solutions increase 850 mb mixing
ratios in excess of 8 g/kg.

A northerly surface pressure gradient will develop and tighten on
Sunday night and Monday behind the frontal boundary. Gusty winds,
possibly reaching advisory levels, could develop through the
Interstate 5 Corridor and across Southern Santa Barbara County on
Sunday night and into Monday morning.

.LONG TERM...(MON-THU)

Model solutions continue to suggest a strong offshore flow pattern
developing Monday through Tuesday, then lingering into midweek.
At least, advisory level Santa Ana Winds look to develop along
with a warming and drying trend for Tuesday and Wednesday. The
offshore flow regime could linger into Thursday. GFS solutions
tighten KLAX-KDAG to -7.5 mb on Tuesday morning.

In wind-sheltered locations, clear skies and less winds will allow
for radiative cooling processes to be more efficient during the
overnight hours. As a result, the interior valleys such as the
Antelope, Cuyama, and San Luis Obispo County Valleys could have
some frost, and maybe freeze conditions for Tuesday and
Wednesday.

Model solutions are struggling with developing a trough over the
Eastern Pacific Ocean for late next week. Timing and run-to-run
consistency issues are plaguing the models at this time, but a
degree confidence exists to bring cooler temperatures and partly
cloudy skies for late next week.

&&

.AVIATION...23/2330Z...

Good confidence with 00Z TAFs. Weak to occasionally moderate LLWS
is possible for KBUR and KSBA from 02Z to 18Z. There is a 20
percent chance of MVFR haze at Coastal TAF sites between 08Z and
20Z.

KLAX...Good confidence in 00Z TAF. There is a 20 percent chance
of MVFR haze between 08Z and 20Z

KBUR...Good confidence in 00Z TAF.

&&

.MARINE...23/830 PM...

Moderate to high confidence in current forecast for the northern
two thirds of the outer waters, with SCA conditions expected
to continue through late Fri night. Lower confidence in the
forecast for the southern outer waters. There is a 30-40% chance
that a SCA will be needed Fri afternoon and evening.

Winds will diminish all areas on Saturday. However for Sunday
through Tuesday, northwest winds will increase to SCA levels with
even a 30% chance of Gale force gusts on Monday.

For the Inner Waters north of Pt Conception, moderate to high
confidence in current forecast. Winds and seas are expected to
remain below SCA levels through Sunday although there is a 20%
chance of SCA level winds Friday afternoon/evening. On Monday and
Tuesday, northwest winds will increase with SCA level winds
likely.

For the waters south of Point Conception, winds and seas will
remain below SCA levels through Sunday afternoon. For Sunday night
and Monday, there is a 50% chance of SCA level northerly winds
across western sections. On Tuesday, the winds will shift to the
northeast with a chance of SCA level winds from Ventura south to
Santa Monica.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PST Saturday for
      zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
There is the potential for elevated to critical fire weather
conditions Monday through Wednesday for portions of Southwest
California. From Monday into Monday night, there is the potential
for strong northerly winds, followed by the potential for
strong Santa Ana winds and low humidities on Tuesday, with gusty
offshore winds lingering into Wednesday.

&&

$$

PUBLIC...Hall/DB
AVIATION...Munroe
MARINE...RAT/DB
SYNOPSIS...STu

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion