Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/28/22

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 800 PM PDT Sat Aug 27 2022

.SYNOPSIS...27/116 PM.

A weak trough over the region this weekend will support increased
night to morning low clouds with below normal temperatures for
late August. A strong ridge will build overhead by mid-week
generating much hotter conditions with triple digit heat likely
for many interior areas.

&&

.SHORT TERM (SAT-TUE)...27/759 PM.

***UPDATE***

Latest satellite/surface observations indicate marine layer
stratus and fog impacting the coastal plain with clear skies
elsewhere. Current AMDAR soundings indicate marine inversion near
1300 feet deep. No unusual winds are observed.

For the immediate short term, only issue will be the marine layer
stratus/fog. Overnight, H5 heights will decrease a bit as a little
upper trough zips across the area. This will allow the inversion
to deepen overnight. With the continued onshore flow, stratus/fog
should make a good push inland overnight, well into the coastal
valleys and potentially even the Santa Clarita Valley. Also,
stratus/fog will likely impact the Salinas Valley overnight.

Overall, the current forecast has good handle on the immediate
short term. So, no significant updates are anticipated at this
time.

***From Previous Discussion***

The cooling trend that began Friday will continue through the
weekend as a weak trough moves through to the north. Gradients
trending onshore again and the marine layer is up to around 1500`.
Expecting another 500` or so of deepening tonight and likely
getting into the San Fernando Valley for the first time in
awhile. Highs for coast and valleys Sunday will be 5-10 below
normal while far interior areas will be near normal. No
thunderstorms expected and likely minimal if any cu in the
mountains as drier southwest flow associated with the trough
pushes all the moisture and instability well to the east.

The weak upper low will linger over northern California through
Monday but then start lifting out later Monday as high pressure
builds back in from the southeast. Most areas will a couple
degrees of warming then several more Tuesday as the high really
strengthens over the southwest. Onshore gradients will be
weakening as well allowing coastal areas to warm up as well.

.LONG TERM (WED-SAT)...27/140 PM.

There is very high confidence in a significant and extended heat
wave for southwest California from mid week through Labor Day
weekend (and possibly beyond). Ensemble solutions from both the
ECMWF and GEFS models are in almost unanimous agreement that a
strong high pressure ridge will encompass most of the western
third of the US starting Tuesday and lasting through the Labor Day
weekend. All the model clusters are in alignment as well, leading
to higher than usual confidence this far out that a significant
heat wave will grip much of the southwest for several days.

In addition to the strong high aloft, models indicate weakening
onshore flow which will delay the arrival of the usual cooling sea
breeze. Highs expected to climb to as high as 100-108 in the
coastal valleys and possibly 110 or higher in the Antelope Valley.
It`s likely that heat advisories and/or warnings will be needed
across a large portion of the forecast area with the possible
exception of some coastal areas, though even there highs will
likely be 5-10 degrees above normal. Peak heat days appear to be
Wed and Thu, but if there is any cooling after that it won`t be
much. Overnight low temperatures expected to be warming as well,
especially in the lower mountains and Antelope Valley, where
overnight temps may not drop below 80.

&&

.AVIATION...27/2351Z.

At 23Z at KLAX, the marine layer was 1400 feet deep. The top of
the inversion was around 2500 feet and 25 Celsius.

High confidence in more expansive ceilings developing tonight
with higher bases compared to last 24 hours. Low confidence on
timing. All flight categories should be in IFR/MVFR when ceilings
present.

KLAX...High confidence in ceilings present tonight and staying
above 010 (higher than last night). 20 percent chance of ceilings
forming as early as 01Z, increasing to 100 percent chance of by
08Z. There is a chance of random breaks 02-06Z. Likely clearing
window 16-18Z. No significant easterly wind component is expected.

KBUR...70 percent chance of ceilings forming tonight. 20 percent
chance of ceilings forming as early as 07Z, and the latest of 12Z.
Likely clearing window 15-17Z.

&&

.MARINE...27/759 PM.

For the Outer Waters, moderate confidence in current forecast.
There is a 60-70% percent chance of Small Craft Advisory (SCA)
level winds through tonight. For Sunday through Tuesday, there is
a 40-50% chance of SCA level winds. For Wednesday and Thursday,
there is a 60-70% chance of SCA level winds.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. Tonight through Tuesday, high
confidence in winds and seas remaining below SCA levels. For
Wednesday and Thursday, there is a 40-50% chance of SCA level
winds in the afternoon and evening hours.

For the Inner Waters south of Point Conception, moderate
confidence in current forecast. Tonight through Tuesday, generally
high confidence in winds/seas remaining below SCA levels although
there is a 30% chance of SCA level winds across the western half
of the Santa Barbara Channel Sunday night. For Wednesday and
Thursday, there is a 30% chance of SCA level winds across western
sections of the southern Inner Waters.

&&

.BEACHES...27/920 AM.

A larger than normal long period southerly swell will bring
elevated surf of 3 to 6 feet to the beaches of Los Angeles
Counties through Sunday night. The largest surf will likely be
across south-facing beaches. There will also be an increased risk
of strong rip currents, creating hazardous swimming conditions at
affected beaches. Please see the product LAXCFWLOX for more
details.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Sunday afternoon
      for zones 87-354-363-364. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Thompson
AVIATION...Kittell
MARINE...RAT
BEACHES...Sweet/Stewart
SYNOPSIS...MW

weather.gov/losangeles

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