005
FXUS66 KLOX 210821
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
121 AM PDT Sat Sep 21 2024

.SYNOPSIS...20/740 PM.

Showers and thunderstorm chances have ended this evening, as an
upper low pressure system moves east of the area. High pressure
will begin to build over the region later tonight into Saturday,
bringing a warming and drying trend to the region through the
weekend and into early next week.

&&

.SHORT TERM (FRI-MON)...20/801 PM.

***UPDATE***

The cold upper low that brought showers and thunderstorms to the
area during the last couple of days is currently centered over
far SE California, and will continue to shift east of the area
tonight. As this occurs, a ridge of high pressure will begin to
build over the West Coast later tonight into Saturday. This will
bring a warming and drying trend to the area that will persist
through early next week, along with a return of coastal low
clouds and fog. Heights aloft will be low enough tonight that a
fairly robust stratus layer is expected to move over the coast and
the coastal valleys overnight into Saturday morning. Expect to
see good clearing in the afternoon across the area, with highs in
the 70s to 80s from the interior coast to the valleys, climbing
into the low 90s for the far interior. Along the beaches, 60s to
low 70s are expected.

***From Previous Discussion***

An active upper low continues to generate showers and thunderstorms
across southern California, though the dry/wet axis continues to
shift towards the east following the low into Arizona. But at
least until around 6pm the eastern portion of LA County will be
susceptible to periods of heavy rain and thunderstorms. At this
time all the activity is in San Bernardino and Riverside counties
but there`s still just enough of a westerly trajectory that could
bring those storms into LA County. Of particular concern is the
area around the Bridge fire, which has the added factor of the
mountain terrain to enhance updrafts. No flood watch is in effect
at this time but chances aren`t zero that very heavy rain could
still develop there and across other areas of eastern LA County.
Based on the lack of cumulus clouds west of there it`s unlikely,
but not impossible, that an isolated shower could drift off the
Tehachapi mountains and move into northwest LA or northeast
Ventura County this afternoon.

After this evening the weather calms down considerably, returning
to typical night and morning low clouds and fog and warming
temperatures. However, models have definitely trended not as warm
early next week as a weak upper low is now favored to develop just
west of the Bay Area Sunday and drift slowly south Monday. Still
expecting a warming trend but perhaps 2-4 degrees cooler than
earlier forecasts.

.LONG TERM (TUE-FRI)...20/209 PM.

Very low impact weather next week with highs mostly within a few
degrees of normal. A little cooling Tue-Thu with that upper low
still lingering and onshore flow increasing. Likely a steady does
of night and morning low clouds and fog at least for coastal
areas.

While the deterministic model solutions show significant
differences for the latter part of next week and beyond and at
least one solution showing a deep trough along the West Coast late
next weekend, the ensemble means favor very little change or
slight warming and overall very low impact weather conditions.

&&

.AVIATION...21/0815Z.

At 05Z at KLAX, the marine layer was 1300 ft deep. The top of the
inversion was at 4000 feet with a temp of 18 C.

High confidence in TAFs for KPMD and KWJF.

Moderate confidence in remaining TAFs due to the uncertainty of
flight cat changes.

There is a 20% chance KPRB remains VFR thru 04Z, and a 20% chance
of LIFR-IFR cigs after 04Z.

There is a chance for VLIFR conds at KSMX (40%) and KSBP (30%)
between through 16Z and again after 03Z.

For coastal sites south of Point Conception, cigs may scatter and
reform, as well as fluctuate between IFR and MVFR through 16Z.
Cigs may return Sunday as IFR.

There is a 30% chance of IFR cigs at KVNY and KBUR through 16Z,
and a 20% chance of remaining VFR through the period.

KLAX...Moderate confidence in TAF. Cigs may scatter and reform
through 16Z. Cigs may fluctuate between BKN008-010 through 16Z,
then lift to BKN018-022 and scatter by as early as 16Z or as late
as 20Z. No significant east wind component expected.

KBUR...Moderate confidence in TAF. There is a 30% chance of
BKN008 cigs through 16Z, and a 20% chance of remaining VFR through
the period.

&&

.MARINE...20/801 PM.

For the Outer Waters (Central coast south to San Nicolas
Islands), high confidence in winds and seas remaining below Small
Craft Advisory (SCA) level thru Wednesday in the northern zone
(off the Central Coast). For the southern zones (Pt Sal to San
Nicolas Island), SCA level winds will continue thru late tonight,
especially from Pt Conception south to an Nicolas Island, before
subsiding. From Saturday thru Wednesday, high confidence in winds
and seas remaining below SCA level, and then there is a 20-30%
chance of winds picking up Wednesday night throughout the Outer
Waters.

For the inner waters along the Central coast, high confidence in
conds remaining below advisory levels through Wednesday.

For the Santa Barbara Channel, moderate to high confidence in the
forecast. SCA level winds will continue in the far western
portion of the zone thru late tonight. Then, moderate to high
confidence in conditions remaining below SCA levels through
Wednesday.

For the inner waters off the coast of LA and Orange Counties,
high confidence in conditions remaining below advisory levels
through Wednesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT early this
      morning for zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Smith
AVIATION...Lund
MARINE...Lewis
SYNOPSIS...MW/Smith

weather.gov/losangeles

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