Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/02/22

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 838 PM PDT Sat Oct 1 2022

.SYNOPSIS...01/917 AM.

A deep marine layer will support continued cool conditions with
widespread night to morning low clouds focused west of the
mountains this weekend. Warming and drying trends are expected
early next week as a ridge of high pressure squashes the marine
layer towards the coast.

&&

.SHORT TERM (SAT-TUE)...01/836 PM.

***UPDATE***

The latest LAX AMDAR sounding indicates the marine layer is
between 2000-2500 feet. The southerly surge today led to no
clearing of low clouds for portions of the Central Coast. Most
areas west of the mountains came in below normal with daytime
highs in the mid 60s cooler coasts to mid 80s warmest valleys.

Without a southerly surge tonight the marine layer depth and
associated cloud coverage will likely be similar, if not less than
this morning through Sunday morning. This would have it
blanketing most, if not all coasts and valleys including the
Salinas Valley by daybreak Sunday. The deep marine layer will
limit night to morning fog potential to coastal foothill to lower
mountain slopes.

Weak offshore trends and a slight increase in 500 mb heights
Sunday will begin to squash the marine layer and delay the sea
breeze, allowing 2-4 degrees of warming for many areas away from
the coast. Low clouds will also burn off earlier in the day,
especially for northern sections of the Central Coast.

***From Previous Discussion***

While near to below normal temperatures will persist west of the
mountains into Sunday, near to slightly above normal temperatures
will continue to far interior areas. A noticeable warm up is
expected to commence in full force early next week, focused across
coastal valleys in particular due to the retreating marine
airmass as well as modest compressional heating due to weak
morning offshore flow from the north by Tuesday (-2 to -3 mb
pressure gradient from Los Angeles to Bakersfield). Daytime highs
at least into the 90s are expected in the warmest areas.

Above and inland from the marine layer will be mostly sunny
although a little push from the east at mid levels may introduce
just enough moisture for afternoon cumulus to eastern Los Angeles
county mountain ridgetops Sunday or Monday afternoons.

Locally gusty (sub-advisory) winds will persist mainly Antelope
Valley foothills through the I-14 corridor through Sunday. Gusty
winds will likely become focused across southwest Santa Barbara
County early next week as weak, but likely sub-advisory
Sundowners develop. Breezy but even lighter northerly winds are
possible across other mountain locales, especially near the I-5
corridor.

.LONG TERM (WED-SAT)...01/128 PM.

Forecast confidence decreases in the extended, especially heading
into next weekend as ensemble (GEFS ECS GEPS) hints at a potential
cut-off low in the region late in the week. Mid-week should
continue to be quiet, relatively small changes in the weight of
the atmosphere (i.e. 500 mb heights) and coastal surface gradients
could play a large role in night to morning low cloud coverage and
related temperature trends. As of now it seems coastal areas are
the best bet for some semblance of night to morning low clouds
(especially Ventura county and points north which is common this
time of year). Near to above normal temperatures are favored
coastal valleys to inland with near to even below normal
temperatures for coastal areas under the influence of a
potentially strong marine inversion. The warmest valleys will
continue to peak into at least the 90s for daytime highs through
at least Friday.

As mentioned earlier much doubt remains about the late week
forecast. Ensemble guidance little in the way of clue on
potential location and strength of a cut-off low pressure system.
There is even an indication that the system may absorb some
moisture from the remnants of Tropical Cyclone Orlene, with a
small (less than 10 percent) chance of the cut-off low pulling
enough moisture into the region for a shower/thunderstorm
potential for Los Angeles/Ventura County mountains. Given the low
confidence scenario, it is best communicated as a 90 percent or
greater chance that quiet weather continues across the region.
Lowering atmospheric heights with the potential for additional
offshore trends should lead to cooling across the interior with
warming trends for some coastal areas. Even with warming in some
areas, temperatures will likely remain safely below any heat
product thresholds.

&&

.AVIATION...01/2346Z.

At 2350Z, the marine inversion at KLAX was based at 2900 feet.
The top of the inversion was 3900 feet with a temperature of 20
degrees Celsius.

Overall, moderate to high confidence in 00Z TAF package. For
coastal and valley sites, high confidence of mostly MVFR cigs
moving back into the airfields tonight, except IFR/LIFR cigs
likely to develop at KSMX/KSBP overnight. Onset and dissipation
times of cigs are +/- 2 hours from TAF timings. High confidence
in CAVU conditions for desert TAFs.

KLAX...Overall, moderate confidence in the 00Z TAF. High
confidence of MVFR cigs returning tonight, however onset and
dissipation times of cigs are +/- 2 hours from current forecast.
No significant easterly wind component is expected.

KBUR...Overall, moderate confidence in 00Z TAF. Timing of return
and dissipation of MVFR conditions could be +/- 2 hours of
current forecast.

&&

.MARINE...01/730 PM.

High confidence in the current forecast with winds remaining
below Small Craft Advisory levels through the weekend, along with
diminishing seas. By Monday winds will begin to increase some,
especially during the late afternoon to evening hours.

SCA level NW winds will be possible across the outer waters by
Monday evening then continue into the middle of next week.

&&

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

&&

$$

PUBLIC...Munroe
AVIATION...Gomberg
MARINE...Sweet/Gomberg
SYNOPSIS...Munroe

weather.gov/losangeles

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



Area Forecast Discussion

National Weather Service Phoenix AZ

 457 PM MST Sat Oct 1 2022

.UPDATE...Updated 00z Aviation Discussion.

&&

.SYNOPSIS...
Storm and shower chances over Phoenix and the lower deserts
will remain fairly modest at only 10 to 15 percent. Slightly
better rain and storm chances will favor the higher terrain of
south-central Arizona and east of Phoenix through Wednesday and
into the late week period. High temperatures will remain slightly
above normal even with a subtle cooling trend during the latter
half of the workweek.

&&

.DISCUSSION...
There is little change in today`s rather stationary weather pattern.
A small cutoff UL low remains over Sonora with a much larger closed
low near the N-Cent Rockies. The large low is flanked to the N,
NW and W by a high amplitude ridge and another UL ridge to its SE
across TX and the Central Plains, effectively forming a rex block.
This puts the area in somewhat of a neutral col with local ACARS
soundings indicating moist SE flow from near H6 down, and drier NW
flow from ~H5 up.

Somewhat anomalously moist PWs are near a temporal, current max
of ~1.00-1.25" around Phoenix and >1.30" for SW AZ. The local
morning soundings and mesoscale analysis indicate a moistened BL
and dry upper-mid levels. Overall the column was not yet very
unstable with late morning CAPE near 700 j/kg, MLCIN of -450 j/kg
and a series of mid and upper level subsidence caps. This could
be considered a conditionally stable to conditionally unstable
situation. GOES IR METSAT also showed mostly clear skies with WV
imagery revealing dry air aloft.

Due to the subtle proximity/influence of the rotating moisture field
and vort disturbances of the Sonoran UL low, models are in good
agreement on keeping the regional PW`s elevated near ~1.2-1.3"
through tonight followed by a gradual 5-day drying trend. Ensembles,
the HREF/family and UAWRF-GFS also depict widely isolated, generally
short-lived storms/showers developing across the region today and
tomorrow which seems likely.

These isolated cells will be capable of producing localized,
fleeting gusty outflows, some dust and brief light to moderate
showers. Most areas will not be impacted by this hit-and mostly miss-
activity with only slight 10-15% chance of showers and storms for
Phoenix, the lower and SW AZ deserts. Highs will not change much and
will top out in the mid-upper 90s around Phoenix and the upper 90s
out west through tomorrow.

From tonight/tomorrow and the first half of the week models agree on
slowly shifting the N low pressure system slowly E and then SE into
the N-Cent Plains and building strong high pressure across the W
and NW CONUS. At the same time at least one or more short wave
vort disturbances with cold air dive off the rear flank of the
main low and rotate through N to E AZ. This will produce moderate
spikes in instability and forcing and will likely trigger
occasionally scattered convective storm activity across N and E AZ
including the high terrain E of Phoenix. This will maintain more
decent 30% storm chances for those high terrain areas starting Sun
through Mon, 20% chances for the midweek, and 10% chances for the
late week period with a gradual decrease in disturbances.

These same mechanisms will maintain 10-15% chances of mostly
widely isolated storms for Phoenix, the lower and SW deserts
through midweek. Highs will nudge down a couple of degrees in the
mid 90s going into the late week but will still manage to remain
slightly above normal.

Late week ensembles and Clusters favor high pressure to the north
and week low pressure aloft and/or the potential for moist SE
undercutting BL and sfc flow developing similar to what occurred
in the region last weekend and early this week. This could
maintain slight rain chances for the lower deserts and high
terrain.

&&

.AVIATION...Updated 2355Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No aviation weather concerns expected through the period. Light
westerly winds with speeds aob 7 kts will continue through the
evening hours, becoming light and variable overnight. Light
easterly winds will predominate through the morning hours with
the easterly direction continuing at KPHX into most of the
afternoon hours, before a southerly to southwesterly switch by
tomorrow evening with light speeds aob 7 kts. Mostly clear skies
expected through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at KIPL will generally favor the SE, while winds at KBLH favor
the S. Expect speeds to mostly remain between 10-15 kts through
the early evening hours with lighter winds with speeds aob 6 kts
during the overnight through tomorrow morning. Expect a FEW mid
and high clouds throughout the next 24 hours.

&&

.FIRE WEATHER...
Anticipate an uptrend in thunderstorm activity this weekend over
south-central and southwest Arizona with ongoing chances Monday
and Tuesday. Rain chances over the lower deserts will remain
modest at only 10 to 20 percent (20-40% higher terrain). Storm
chances will retreat to the higher terrain of south-central
Arizona by Wednesday with lingering chances of 15-30% through
Friday. High temperatures will remain slightly above normal
before a subtle cooling trend during the latter half of the next
workweek. MinRH will range from 25-35% across the forecast area
through Monday before decreasing 5-10% by Wednesday - mainly over
southeast CA and southwest AZ (little change or even slightly
higher over the higher terrain of south-central AZ). Max RH will
range from 50-90% tonight before decreasing 10-20% by Monday night
over southeast CA and southwest AZ with an additional 5-10%
decline by Wednesday night across the forecast area. Apart from
thunderstorms, winds will tend to follow familiar diurnal
patterns.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Sawtelle
AVIATION...Lojero/Feldkircher
FIRE WEATHER...AJ