642
FXUS66 KLOX 261128
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
428 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...26/0327Z.

At 0006Z over KLAX, the marine layer was 1300 ft deep. The top of
the inversion was 2000 ft with a temperature of 24 Celsius.

High confidence in 00Z desert TAFs. Cigs due to marine layer
clouds leads to moderate to low confidence in remaining TAFs.
Could see cigs delayed 1-4 hours from the forecast arrival times.
Cigs may be slow to clear for KSMO, KLAX, and KLGB. Moderate to
high confidence in ceilings.

KLAX... Moderate to low confidence in 00Z TAF. Cigs may arrive 1-4
hours later than forecast. LIFR conditions may be delayed as well
by 1-3 hours. High confidence in no significant east wind
component.

KBUR...Good confidence cigs will return but low confidence in
timing. There is a 30% chance of VLIFR fog 11-15Z.

&&

.MARINE...25/845 PM.

High confidence in Small Craft Advisory (SCA) winds through
tonight for the offshore waters from Point Conception to San
Nicolas Island. Moderate confidence in winds increasing to SCA
level (50-60% chance) for the outer waters (along the Central
Coast and south to San Nicolas Island) Thursday afternoon and
night. Then, high confidence in fairly light winds (staying below
SCA levels) Friday morning through Saturday morning. Moderate
confidence in SCA winds returning Saturday or Sunday and
persisting through Monday before another weakening period returns
Tuesday and Wednesday.

Dense fog with visibilities under 1 mile will be possible through
at least Friday, with the highest chances each night and morning
and along the Central Coast.

&&

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

&&

$$

PUBLIC...Hall
AVIATION...Phillips
MARINE...RK/Lund
SYNOPSIS...Hall

weather.gov/losangeles

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