442
FXUS66 KLOX 050056
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
456 PM PST Wed Dec 4 2024

Updated Aviation Discussion

.SYNOPSIS...04/215 AM.

Above normal temperatures are expected through the week, peaking
Friday and Saturday with highs in the 70s and 80s. Locally gusty
Santa Ana winds are possible Friday into early next week. Skies
will be mostly clear to partly cloudy with areas of morning low
clouds and fog at times. No rain expected through the end of next
week.

&&

.SHORT TERM (TDY-SAT)...04/142 PM.

Overall, 12Z models in good synoptic agreement through the short
term period. At upper levels, a low will meander over northern
Mexico while a ridge noses in across Central California. Near the
surface, weak onshore flow will continue through tonight then
offshore flow will increase Thursday through Saturday.

For tonight/Thursday morning, main concern will be the extent of
the marine layer stratus/fog. Current sounding data indicates
marine inversion near 1000 feet deep and will likely not change in
depth appreciably overnight with the inversion remaining
moderately strong. At the same time, surface pressure gradients
will be turning weakly offshore. So, pretty confident that some
stratus/fog will develop across the coastal plain, but low
confidence in the areal extent. Any fog that develops will likely
be dense, so advisories may need to be issued by the next shift.

For Thursday afternoon through Saturday, main focus is on offshore
winds. At this time, models indicate increasing offshore gradients
through Saturday, but upper level support is somewhat limited. So
at this time, will only expect generally weak north to northeast
winds (gusts 25-35 MPH with local gusts to 45 MPH) across the
Santa Ana prone areas of Ventura/LA counties as well as the
mountains and foothills of San Luis Obispo and Santa Barbara
counties. Chances of any wind advisories are about 20-30%.

With the offshore winds and rising thicknesses/H5 heights, warm
and dry conditions can be expected. High temperatures west of the
mountains will top out in the 70s to lower 80s Friday/Saturday.
Elevated to briefly critical fire weather conditions can be
expected with relative humidity dropping into 12-25% range
Thursday/Friday and 8-15% on Saturday.

.LONG TERM (SUN-WED)...04/142 PM.

For the extended, 12Z models continue to exhibit decent synoptic
agreement through the extended period. Main feature of note will
be a sharp upper level trough that drops southward across the
Great Basin Monday/Tuesday. This will set the stage for a decent
offshore wind event.

For Sunday, conditions are expected to be on the quiet side. The
northeasterly winds from Friday/Saturday will shift to the
northwest. Gusts of 20-40 MPH will be likely in the northerly
wind-prone spots (like the I-5 Corridor and Santa Ynez Range).
Partly cloudy skies will prevail with cooler temperatures.

For Monday through Wednesday, attentions turns to potential Santa
Ana event. Deterministic models indicate peak surface gradients
between -6 and -8 mb with decent upper level wind support
(especially on the GFS), indicating the potential for a moderate
to strong event. Looking at the ensembles, the various member
solutions indicate a moderate event which has been very consistent
the last few days. So for the afternoon forecast, will go with the
idea of a moderate Santa Ana wind event (with a 20-30% chance of a
strong event) for Ventura/LA counties and widespread gusty
northeasterly winds across interior sections of San Luis Obispo
and Santa Barbara counties. Various wind advisories (and possibly
a couple of wind warnings) will be likely in the Monday to
Wednesday time frame. Also, this event will be very dry with
relative humidity dropping into the 5-15% range (with poor
overnight recovery). So, there is a very good chance of widespread
critical fire weather conditions in the Monday to Wednesday time
frame and non-routine fire products will be likely.

&&

.AVIATION...05/0054Z.

At 0033Z at KLAX, the marine layer was 800 feet deep. The top of
the inversion was at 3400 ft with a temperature of 17 C.

High confidence in TAFs for KPRB, KPMD, and KWJF.

Low to moderate confidence in remaining TAF sites. For all
coastal sites, timing of cig arrivals may be off by +/- 3 hours
and lowest flight cat may be off by one. There is a 20%
chance that cigs and low VSBY will not reach KBUR and KVNY. For
sites south of Point Conception, there is a 20-30% chance of
dense fog with VSBY as low as 1/4SM-1/2SM at times during cigs.

KLAX...Low confidence in TAF. Flight cat chances may be off by
+/- 2 hours. There is a 20% chance for VSBY between 1/4SM and
1/2SM between 07 and 15Z. No significant east wind component is
expected.

KBUR...Low confidence in TAF. Timing of cig arrival tonight may be
off by +/- 3 hours, and there is a 20% chance that cigs will not
reach the site.

&&

.MARINE...04/123 PM.

For the Outer Waters moderate confidence in the forecast. There
is a 40-50% chance of Small Craft Advisory (SCA) level wind gusts
beginning late tonight and lasting into the morning. SCA level
winds are more likely (60-70%) to be widespread in the late
morning or early afternoon hours Thursday. SCA winds will likely
(50-70% chance) persist through late Friday night, with brief
lulls possible at times. Seas will begin to build Sun and Mon
across the Outer Waters, possibly (40-50% chance) reaching SCA
levels, with best chances in the northern portions of the Outer
Waters. On Sun there is a 40-50% chance of SCA level winds, with
best chances in the northern portions.

For the the inner waters north of Point Sal, and in the inner
waters south of Point Conception, moderate to high confidence in
the forecast. SCA conds are not expected except for a 20% chance
of brief NE to E gusts in the northern inner waters Thursday and
Friday morning thru afternoon and a 30% chance of SCA level NE
winds nearshore from Ventura to Santa Monica during the late night
thru morning hours Thu night thru Sat.

Areas of dense fog will affect the coastal waters through early
this afternoon, and will likely return during the night through
morning hours thru Fri.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 AM Thursday to 3 AM PST
      Saturday for zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Thompson
AVIATION...Schoenfeld
MARINE...DB/Lewis
SYNOPSIS...MW

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox