Acton Weather

000
FXUS66 KLOX 260634
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1134 PM PDT Sun Sep 25 2022

.SYNOPSIS...25/413 AM.

Ridging aloft and an associated heatwave will peak early this
week before broad troughing and cooler conditions build into the
region heading into next weekend. Night to morning clouds may
become sparse early next week before potentially becoming
widespread later in the week.

&&

.SHORT TERM (SUN-WED)...25/858 PM.

Another hot day for areas away from the coast, with triple digit
readings being recorded at Woodland Hills, Northridge, and Van
Nuys. Earlier this afternoon, we saw a few convective storm cells
develop across the mountains of LA/Ventura counties, but did not
see any lightning with these storms.

Current satellite imagery showing low clouds and fog
returning to the Central Coast this evening, and will potentially
develop across the Ventura County coastal plain later tonight.
With a low and strong inversion in place, will have the potential
for patchy dense fog for these areas. Another item of note is
the return of some gusty sundowner winds, with gusts of 30 to 40
mph across the western Santa Ynez range and adjacent foothills.
As of 8 pm, the Santa Barbara-Santa Maria pressure gradient was
-3.5 mb.

Latest 00Z NAM model continue to trend pressure gradients slightly
offshore the next couple of mornings, while nudging up 950 mb
temperatures. So still looks like Monday/Tuesday are on track
to be warmest days of current heat wave for areas away from the
coast. Current heat advisories/warnings generally look good
for next couple of days, but later shifts may need to consider
downgrading the interior LA county coast from a Heat Warning to
a Heat Advisory as models continue to trend temperatures down
slightly for the coastal plain from earlier forecasts. Also,
conditions are a bit drier on Monday, so only expecting some
cloud buildups over the local mountains, and no threat of
thunderstorms.

*** From previous discussion ***

Forecast-wise, main issue for the short term will continue to be
the heat. Overall with the high pressure aloft and the weak
gradients, it will be very warm the next couple of days. However,
most models continue to slightly trend downward with the high
temperatures which tempers forecast confidence. Based on available
guidance, will keep EXCESSIVE HEAT WARNINGS in effect for the LA
Valleys and Interior Coastal Plain, but will adjust ending time to
Tuesday evening (instead of Wednesday evening). Will keep HEAT
ADVISORIES in effect for the Ventura Valleys/Santa Monica
Mountains through Tuesday evening, but will cancel advisories for
the immediate coastal zones. There is a chance that the Warnings
may need to be downgraded to advisories by future shifts, but will
keep things as is for now. By Wednesday, all areas are expected to
be below any heat product thresholds. See LAXNPWLOX for the latest
details about the heat products.

The secondary issue for the short term will be the potential for
Sundowner winds. High resolution models increase the northerly
gradients across the western Santa Ynez Range which will result in
increasing northerly winds. At this time, expect winds to remain
just below advisory-levels tonight, but there is a decent chance
of advisory-level winds Monday evening and again Tuesday evening.

.LONG TERM (THU-SUN)...25/205 PM.

For the extended, models continue to be on the same general
synoptic page. Essentially, the area will be between an upper
level low that moves into the north central part of the country
and a weak upper level high trying to establish over the desert
Southwest.

Forecast-wise, the above pattern should result in rather benign
weather for the district. Onshore gradients will be on a slow
increasing trend, so stratus/fog should gradually become more
widespread across the coastal plain and lower coastal valleys.
Other than any potential stratus/fog, skies should remain mostly
clear through the period. As for temperatures, will anticipate a
gradual cooling trend for all areas.

&&

.AVIATION...26/0633Z.

At 0445Z at KLAX, the marine layer was 600 feet deep. The top of
the inversion was near 1400 feet with a temperature of 29 C.

High confidence in valley and desert TAFs.

Moderate confidence in TAFs for KSBP and KSMX where there is a 25
percent chc of 1/4SM FG conds 11Z-15Z.

There is a 30 percent chance of no cigs at KOXR and KCMA.

There is a 20 percent chance of IFR/LIFR cigs at KSBA, KSMO, KLAX
and KLGB 12Z-16Z.

KLAX...Moderate confidence in TAF. There is a 20 percent chance
of 4SM OVC006 conditions 12Z-16Z. No significant easterly wind
component is expected.

KBUR...High confidence in VFR conditions through TAF period.

&&

.MARINE...25/1048 PM.

A Small Craft Advisory (SCA) level was issued for gusty winds
through the Santa Barbara Channel, with SCA level gusts reaching
the Ventura County Coast this evening. Winds will fall below SCA
levels for this area overnight, but a SCA is likely needed (70%
chance) for the Santa Barbara Channel again tomorrow
afternoon/evening.

The current SCA for the outer waters south of Point Sal looks on
track, and winds should spread into the northern outer waters by
Monday afternoon/evening. Looking through the week, there is a
good chance (60-80%) for SCA winds throughout the outer waters
and the inner waters north of Point Sal during the evening hours
through Thursday. SCA winds appear to be less likely for the
Santa Barbara Channel Tuesday (30%), and Wednesday (50%) during
the afternoon/evening hours.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning in effect from 10 AM Monday to 8 PM
      PDT Tuesday for zones 88-365-547-548. (See LAXNPWLOX).
     Heat Advisory in effect from 10 AM Monday to 8 PM PDT Tuesday
      for zones 356>359-363. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 2 AM PDT Monday for zone
      650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 2 AM PDT Tuesday for
      zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Gomberg/Thompson
AVIATION...Rorke
MARINE...Phillips/Sweet
SYNOPSIS...Munroe

weather.gov/losangeles

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