Acton Weather

000
FXUS66 KLOX 301134
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
334 AM PST Tue Nov 30 2021

.SYNOPSIS...30/331 AM.

High pressure aloft and above normal temperatures will continue
through this week. Gusty northeast Santa Ana winds are expected
today into Wednesday. A cool down is expected Thursday through
Saturday with the return of low clouds and fog to coastal areas.
A slight warming trend is expected on Sunday and Monday

&&

.SHORT TERM (TDY-THU)...30/329 AM.

Current GOES-17 Fog Product imagery shows much more widespread low
cloud cover as compared to the last few mornings. Despite a
non-existent marine layer (rather a surface-based inversion), an
eddy circulation has assisted in bringing low clouds to the LA and
Ventura County coastal plains. Current observations show
widespread dense fog, so a Dense Fog Advisory will be in effect
through 8am for both the LA and Ventura County coasts. Extra time
should be given for the morning commute as visibility as low as a
quarter mile or less will lead to potentially dangerous driving
conditions, especially on the major freeways. Dense fog is also
possible around Santa Barbara through the morning.

High-resolution models indicate strengthening offshore flow
through late morning over the LA and Ventura County mountains and
valleys and less so near the coast. Winds are expected to gust
between 20 and 30 mph across Santa Ana wind-prone areas of LA and
Ventura counties away from the coast with isolated gusts to 40 mph
in favored windy spots. It will be another very warm day across
the area. Have gone with a fairly persistent high temperature
forecast based on similar conditions to yesterday. Have bumped up
temperatures slightly near the coast as well as across the
Central Coast with the breezier offshore winds. The one caveat
will be for the LA and Ventura County coastal areas. Clouds may
linger into the late morning as offshore winds ride over the
inversion which will limit the amount of daytime heating, so
temperatures may be cooler than forecast.

Offshore pressure gradients strengthen a bit on Wednesday morning.
Models also indicate better upper-level support and cold air
advection so offshore winds are expected to be stronger. The local
high-resolution WRF has backed down a bit on winds, so gusts of
20-40 mph still seem reasonable for the wind-prone valleys and
mountains in LA and Ventura Counties. With the better upper and
thermal support, winds will likely reach the Ventura County
coastal plain, although weaker than the valleys. Wind Advisories
may be needed for the valleys and mountains. Breezy Santa Lucia
winds are also expected to continue on Wednesday morning, but the
WRF shows them weaker than today. Temperatures will remain quite
warm, though lowering thicknesses and cooling 950 mb temperatures
may bring some cooling to the interior. The coastal areas will
likely warm up some due to more offshore wind and no cloud cover.
There is a chance for more record high temperatures today and
Wednesday away from the coast.

On Thursday, a weak upper-level low to the south creeps northward
and gradients trend onshore. A major cooling trend will ensue and
temperatures will drop back into the 70s across the board. Some
high clouds may spread over the area and there will likely be a
return of widespread marine layer stratus over the coasts
overnight into Friday morning.

.LONG TERM (FRI-MON)...30/330 AM.

More cooling is expected on Friday then remain fairly stagnant on
Saturday as onshore flow makes its return. Despite the cooling,
temperatures will still be around 5 to 10 degrees above normal
away from the immediate coast. Night through morning marine layer
stratus will continue across the coastal areas, and may filter
into the lower coastal valleys. Models and their ensembles are in
agreement with rebuilding the upper-level ridge over the Eastern
Pacific late Saturday into Sunday and nudging it into California.
Pressure gradients shift back to weakly offshore and this will
start a new brief warming trend on Sunday and Monday. Ensembles
also indicate an uptick in northeast winds through the Santa Ana
corridor, but there is still a decent amount of spread. There is
also still a certain degree of spread in high temperature
possibilities among the EPS, GEFS, and the NBM.

&&

.AVIATION...30/0619Z.

At 0539Z at KLAX, the marine layer was around 70 feet deep. The
top of the inversion was at 1700 feet with a temperature of 23 C.

High confidence in desert and valley TAFs. Moderate to low
confidence in remaining 06z TAFs. Cigs with LIFR to VLIFR conds
are expected across most coastal sections of L.A. and VTU Counties
tonight after midnight, and vis may continue to fluctuate. Lower
confidence on clearing times.

KLAX...Low confidence in the 06z TAF due to uncertainty in vis and
clearing times. No significant east wind expected.

KBUR...High confidence in TAF with VFR conds thru the period.

&&

.MARINE...29/909 PM.

Areas of dense fog will affect the coastal waters through Tue
morning with a marine weather statement in effect. Visibilities
under one quarter mile should be expected.

Across the outer waters, low to moderate confidence in Small
Craft Advisory (SCA) level NW winds continuing across zones
PZZ670/673 through Tue evening. There is a 30% chance of SCA
level winds across the southern zone (PZZ676) tonight and Tue,
mainly NW of San Nicolas Island. SCA conds are not expected late
Tue night thru Fri.

Across the inner waters n of Pt. Sal, SCA conditions are not
expected thru Fri.

In the SBA Channel, there is a 40% chance of SCA level NE winds
from Ventura to Pt Mugu and out to Santa Cruz Island Wed morning.
Otherwise, SCA conds are not expected thru Fri.

Across the southern inner waters, there is a 40% chance of SCA
level NE winds from Point Mugu to Santa Monica Wed morning.
Otherwise, SCA conds are not expected thru Fri.

&&

.FIRE WEATHER...29/143 PM.

An extended period of gusty northeast winds and low humidities
will bring elevated to brief critical fire weather conditions
mainly away from the coast through at least Wednesday. Northeast
wind gusts of 20 to 35 mph are expected in parts of the mountains
and valleys of Los Angeles and Ventura counties during much of
this time. Wednesday should be the windiest day of the week with
peak wind gusts of 25 to 40 mph through the usual Santa Ana wind
corridor. The strongest winds will be limited to more inland
valley and mountain areas, with lesser wind speeds down into the
Ventura County coastal plain.

Many sites away from the coast are reporting minimum humidities
between 8 and 18 percent today and should increase slightly on
Tuesday, then slightly lowering again on Wednesday. The lowest
values will mostly be between 10 and 18 percent on Wednesday.
Very weak offshore flow continues on Thursday and northeast winds
will weaken. The combination of gusty northeast winds and these
humidities will create elevated to briefly critical fire weather
conditions through Wednesday and elevated on Thursday. Red flag
conditions are not expected to be met at this time, especially
since the strongest winds will be Wednesday morning and the lowest
RH will be in the afternoon.

Gusty offshore winds will also blow through the Santa Lucia
mountains and adjacent foothills through Wednesday, however
humidities in this area will should remain above critical levels.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory in effect until 8 AM PST this morning for
      zones 40-41. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 PM PST this evening
      for zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

No significant hazards expected.

&&

$$

PUBLIC...Stewart
AVIATION...Phillips
MARINE...Gomberg/Sweet
FIRE...Jackson
SYNOPSIS...Stewart

weather.gov/losangeles