113
FXUS66 KLOX 261258
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
558 AM PDT Thu Sep 26 2024

.SYNOPSIS...26/418 AM.

A warming trend will develop away from the coast through Friday as
high pressure to the east nudges into the region. At the coast,
onshore flow will keep a persistent marine layer and stronger sea
breeze in place and moderate the warming trend closer to
persistence. Night through morning low clouds and fog will
struggle to clear through the weekend. Cooler temperatures are
forecast for Saturday, then a significant warming trend is on tap
for early next week as high pressure to the east builds in again.

&&

.SHORT TERM (TDY-SAT)...26/427 AM.

The latest fog product imagery shows clouds trying to become more
entrenched along the Central Coast, while struggling to form in
most remaining coastal and valley areas this morning. The area
sits under a deformation zone between an upper-level trough
stretching farther to the southwest and an upper-level ridge to
the east in southern New Mexico. The marine layer stratus deck is
likely being disrupted by the deformation zone overhead early
this morning. The trough will continue to retrograde to the
southwest through this evening, while ridging to the east
replaces it. A warmer day looks on tap for today and Friday away
from the coast and outside the marine influence. 500 mb heights
climb over the region today and Friday, despite onshore pressure
gradients slightly strengthening through Saturday. A more June-
like pattern is looking to set up with stronger onshore flow and
rising heights over the coming days. Clouds will likely struggle
to clear away from the coast the next several days as high
pressure will likely tighten the marine inversion, decrease mixing
at the top of the marine layer, and delay clearing.

The trough to the southwest will advance back to near Point
Conception by Saturday night. Onshore pressure gradients trend
more strongly onshore for Saturday and some cooling should
develop. The beaches and immediate coastal locales will likely
continue to be shrouded in clouds.

.LONG TERM (SUN-WED)...26/427 AM.

The cut-off trough will play around with the area for the
extended period, moving over southern and central California for
the weekend, but then pulling back offshore for next week. 500 mb
heights increase between Sunday and Tuesday and temperatures will
likely warm well above normal between Monday and Tuesday.
Temperatures break away from NBM values during this period to
emphasize a hot weather pattern developing. Heat headlines may be
needed across portions of the area between Monday and Tuesday as
the air mass warms and temperatures rise to between 15 and 20
degrees above normal for this time of year.

While not certain, pattern recognition in the deterministic
solutions would suggest a non-zero chance of afternoon and
evening showers and thunderstorms between Tuesday and Wednesday.
A longer duration of southeast flow aloft develops with the
trough retrograding offshore, and this could bring some sub-
tropical moisture northward into the region from the remnants of
Tropical Cyclone John. A few members of the GEFS and EPS pick up
on the possibility of convection developing, but even more members
picked up precipitable water values climbing for late in the
period. The forecast ensembles suggest there is a 20 percent
chance of precipitable waters value climbing above 1 inch at KLAX
on Tuesday afternoon, which is more than ample for afternoon and
evening convective showers.

There is still quite a bit of spread, but forecast ensembles are
starting to suggest cooling for Wednesday and next Thursday.

&&

.AVIATION...26/1258Z.

At 12Z at KLAX, the marine layer was 1500 ft deep. The top of the
inversion was 3900 ft with a temperature of 22 Celsius.

Low clouds were widespread on the Central Coast, in the Santa Ynez
and Salinas Valleys and in coastal sections of L.A. County. There
were patchy low clouds in coastal sections of Ventura County and
southern SBA County. There is a chance that clouds could briefly
push into the valleys. Conds were mostly IFR to LIFR, except
locally low MVFR in coastal L.A. County. Expect skies to clear by
mid morning in the valleys and late morning on the coastal plain,
except cigs could linger at some beaches into the afternoon.
Expect widespread low clouds in coastal areas tonight, as well as
in the Santa Ynez Valley, with patchy low clouds in the valleys of
VTU and L.A. Counties. Conds will be mostly IFR to LIFR.

KLAX...Low to moderate confidence in the 12Z TAF. There is a 30%
chance that cigs could lower into the IFR category thru 17Z.
There is a 20% chance that cigs could scatter out by 16Z. There is
a 30% chance that cigs will arrive as early as 03Z this evening.
High confidence in no significant east wind component.

KBUR...Good confidence in TAF. There is a 10-20% chance of IFR
cigs thru 16Z this morning, and after 09Z tonight.

&&

.MARINE...26/535 AM.

In the outer waters, low to moderate confidence in the forecast thru
Fri eve. While there may be local advisory level gusts during the
afternoon/eve hours today and Fri, winds are expected to mostly
remain below Small Craft Advisory (SCA) thru Fri night. However,
there is a 40% chance that SCA level gusts will become widespread
enough to require an advisory, especially around Pt. Conception.
From Sat thru Mon night, high confidence that winds will remain
below SCA levels. However, there is a 30% chance of SCA level seas
late Sat thru Mon, highest chance in the northern areas.

Across the inner waters north of Pt Sal, the Santa Barbara
Channel, and inner waters from Pt Mugu southward, moderate to high
confidence that winds and seas will remain below SCA levels thru
Mon night. There is a 20-30% chance of SCA level winds this
afternoon/eve, mainly in western and southern portions of the
Santa Barbara Channel, and from near Anacapa Island to Point Dume.

Patchy dense fog with visibilities of 1 NM or less may affect the
coastal waters this morning, and again tonight/Fri morning, with
the highest chances off the Central Coast.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...Hall
AVIATION...DB
MARINE...DB
SYNOPSIS...Hall

weather.gov/losangeles

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