Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/24/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 915 PM EDT Sat Sep 23 2023

.Forecast Update...
Issued at 915 PM EDT Sat Sep 23 2023

IND ACARS and Hi-Res soundings continue to show a very dry boundary
layer overnight. Dew points have come up a but after diurnal mixing
ended with sunset. Still, there are very large temperature and dew
point spreads. In addition, light winds will continue mostly at 5
knots or more overnight, further supplying dry conditions. So, as
was the case last night, fog should not be an issue with only very
brief light fog at worse over sheltered and low lying areas or near
streams and corn fields. Satellite was showing some thinning cirrus
moving across, and also some debris is possible over the Wabash
Valley associated with the Ozarks convection. Radiational cooling
will allow for overnight lows in the 40s over sheltered, mostly
northeastern counties.

&&

.Short Term...(This evening through Sunday)
Issued at 258 PM EDT Sat Sep 23 2023

- Mostly clear and pleasant overnight
- Mostly sunny and warm on Sunday

Surface analysis early this afternoon continued to show a ridge of
high pressure across Indiana, stretching south across Indiana. This
high pressure system was centered over Quebec and Ontario. Aloft a
ridge axis is shown to stretch from the southern plains across the
mid-Mississippi Valley, across Indiana to the Great Lakes. This was
resulting in subsidence across the area. Windward side flow on this
ridge was pushing clouds and precip associated with low pressure
over the plains states north and staying west of Indiana. Strong
surface low pressure was found over NC/VA.  GOES16 shows clear skies
across Indiana as subsidence was in place under the ridge aloft. Dew
points were quite dry in the 40s.

Tonight...

Little change is expected in the overall pattern. Models continue to
show subsidence and a dry column in place overnight as Indiana will
remain under the influence of the surface high pressure system and
the ridging aloft. Forecast soundings remain dry. Some weak cold air
advection today will allow for slightly cooler low temperatures
tonight. Thus expect clear and pleasant conditions with lows in the
lower 50s.

Sunday...

Slight changes begin to take shape in our weather pattern on Sunday,
but overall, this will have little overall impact on the sensible
weather. The upper ridge is depicted to drift east  of Indiana along
with the inverted surface ridge of high pressure.This will allow the
upper low over the western plains to drift to the upper midwest
along with its associated surface low.  All of this will result in a
more southerly component to surface winds on Sunday, allowing for
slightly warmer high temperatures in the lower and middle 80s.
Again, forecast soundings and time heights show a dry column with
unreachable high temperatures. Thus, mostly sunny and warm.

&&

.Long Term...(Sunday night through Saturday)
Issued at 258 PM EDT Sat Sep 23 2023

Building surface high pressure across eastern Canada will promote
generally easterly flow for the first half of the coming week.
Currently, flow is out of the northeast and is quite dry with dew
points in the mid 40s. Low-level moisture may increase somewhat in
the days ahead as moisture from Tropical Storm Ophelia is sent
westward. The increased moisture should allow fire weather
conditions to improve somewhat.

Meanwhile, to our west, a closed low over the northern Plains should
weaken through tomorrow. Guidance largely depicts this feature
remaining cut off from the mid-latitude westerlies and drifting
southeastward. That should bring the system over Indiana by late
Tuesday, albeit with further weakening. Some showers may arrive well-
ahead of the core of the closed low late Sunday night or early
Monday...but these should be few and far between and mainly near the
Illinois border.

There remains some discrepancies within guidance regarding the
strength of the closed low. Additionally, low-level forcing appears
weak with only modest upper-level support. Nevertheless, enough
instability and forcing should be present for scattered showers and
thunderstorms. Will plan on capping PoPs at chance for now given the
above. Shear appears weak as well, so any storms that develop should
be pulse or loosely organized clusters with low severe potential.

With the closed low overhead or nearby, along with prolonged cloud
cover...moderated temperature are expected this week. The diurnal
curve will be flattened somewhat with highs in the mid 70s and lows
near 60. These values are still within the seasonable range for this
time of year.

By late in the week/next weekend our closed low should be out of the
area, with renewed ridging over the Plains. Some hints in guidance
of residual troughing to our east prompting a return to easterly low-
level flow. Ensemble guidance diverges quite a bit, however, so
forecast confidence decreases. Nevertheless, improving weather
currently appears to be the most likely scenario given the exit of
the mid-week closed low.

&&

.Aviation...(00Z TAF Issuance)
Issued at 712 PM EDT Sat Sep 23 2023

Impacts:

- None

Discussion:

VFR conditions will continue as soundings continue to show very dry
air in place in the boundary layer and dew points are some 10
degrees lower than 24 hours ago, and there was no fog earlier this
morning. In addition, winds will remain out of the northeast 5 knots
or so. The only cloud cover will be some high clouds seen moving
into the Wabash Valley on satellite. Winds will shift to ESE around
daybreak.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Update...MK
Short Term...Puma
Long Term...Eckhoff
Aviation...MK



Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 834 PM PDT Sat Sep 23 2023

.SYNOPSIS...23/834 PM.

Temperatures will gradually warm in most areas for the remainder
of this weekend into early parts of the upcoming week, approaching
and locally exceeding normal readings by the middle of the week.
Temperatures could even reach the lower 90s in a few locations
over the interior valleys on Tuesday and Wednesday. Gusty
Sundowner winds are expected to peak over southern Santa Barbara
County on Tuesday into Wednesday. A cool-down is expected later
in the week and into next weekend, as a large weather disturbance
begins to affect the region and onshore flow increases.

&&

.SHORT TERM (SAT-TUE)...23/833 PM.

Current satellite imagery showing mostly clear skies across the
district this evening, with the onset of low clouds and fog
delayed until later tonight. The marine layer depth is a bit
shallower than last night as a weak upper level ridge of high
pressure builds over the region. 00Z Vandenberg sounding showing
the marine layer depth around 2000 feet this evening, while ACARS
data showing a marine layer depth around 1400 feet across the LA
Basin. Weak pressure gradients continue today across the region,
however there is some locally gusty northwest winds up to 30 mph
this evening near Gaviota/Refugio this evening.

A gradual warm-up started today, with highs climbing into the
lower to mid 80s across warmer valleys and deserts. This warming
trend will continue across inland areas through Monday as
west-southwesterly flow aloft persists above a generally weak
surface pressure gradient.

*** From previous discussion ***

Through Monday, nighttime and morning low clouds and fog will be
possible over coastal areas and nearby valleys of SLO and western
Santa Barbara Counties with a shallow marine layer. Otherwise,
mostly clear skies are expected, supporting ample daytime heating
each day. Despite the gradual warming, temperatures are expected
to remain a few to several degrees below normal Sunday and Monday.

By late Monday night and especially by Tuesday, LAX-BFL and SBA-
SMX pressure gradients turn decidedly offshore and strengthen.
This will further support the aforementioned warming trend, along
with clearing of any marine stratus/fog. By Tuesday, high
temperatures are expected to reach into the 80s in many areas --
i.e., readings nearing normal or exceeding average by a few
degrees. A few locations over the interior valleys could have
Tuesday high temperatures reaching the lower 90s.

These developments are forecast to be in response to surface high
pressure building north of the area, beneath the southern rim of
a large, deep cyclone being reinforced across the Pacific
Northwest. While large-scale ascent and any precipitation are
forecast to remain north of the area, the increasing flow aloft
combined with the strengthening surface pressure gradient are
expected to support Sundowner winds over the mountains and nearby
coast of southern Santa Barbara County. Such winds could develop
as early as Monday evening and then strengthen later on Tuesday.
Wind gusts of 35-50 mph will be possible, and there is a chance
(around 40-50 percent) for wind headlines to become necessary in
these areas. Gusty northwest winds of 30-40 mph will also be of
concern at times for portions of the I-5 corridor, Antelope
Valley, and Central Coast.

.LONG TERM (WED-SAT)...23/225 PM.

The offshore pressure gradients will likely peak Tuesday night
and early Wednesday, on the order of 4.0-4.5 mb (for LAX-BFL,
SBA-SMX, and SBA-BFL). This will prolong the gusty Sundowner wind
pattern into Wednesday over southern Santa Barbara County, with
locally gusty winds also continuing over portions of the I-5
corridor, Antelope Valley, and Central Coast. Near to slightly
above normal temperatures are expected over most areas again on
Wednesday, with temperatures well into the 80s and lower 90s in
many areas away from the coast. Given the continued offshore
gradient, albeit weakening on Thursday, marine stratus and fog
will be unlikely through Thursday. However, temperatures are
expected to cool by 2-5 degrees going into Thursday, as a broad
upper trough begins amplifying over the area.

The onset of cooler temperatures on Thursday will be the beginning
of a cool-down that is forecast to continue into next weekend.
There is strong consensus among deterministic/ensemble model
solutions that large-scale troughing remains anchored over the
western states, and that further amplification of the cyclonic
flow corresponds to additional episodes of cooling across the
region through next weekend. Moreover, confidence is high that the
large-scale pattern favors strengthening onshore flow and a
deepening marine layer late in the week and during next weekend.
High temperatures could be 5-15 degrees below normal next weekend,
perhaps even cooler. Despite growing confidence in cooler
conditions, there are still notable differences among model
solutions regarding the details of timing and magnitude of trough
amplification. This extends to uncertainty in just how cool
conditions will become, along with day-to-day variations in
temperatures. While the most-likely outcome will be a dry pattern,
there is an outside chance of some light rain by the end of next
weekend or early in the following week, depending on the exact
evolution of the trough.

&&

.AVIATION...24/0246Z.

At 00Z, the marine inversion at KLAX was 1600 feet deep. The top
of the inversion was 2600 feet with a temperature of 21 degrees
Celsius.

Overall, moderate confidence in 00Z coastal TAFs and high
confidence in valley/desert TAFs. Lower confidence for coastal
sites due to uncertainties in the arrival times of cigs.

KLAX...Moderate confidence in 00Z TAF. Cigs may arrive 1-2 hours
later than forecast with come uncertainty in flight category
(equal chance of MVFR or IFR CIGs). No significant easterly wind
component is expected.

KBUR...High confidence in 00Z TAF. There is a 20% chance of
MVFR/IFR CIGs 12Z-16Z.

&&

.MARINE...23/816 PM.

For the Outer Waters, moderate to high confidence in current
forecast. Through tonight, there is a 70% chance of Small Craft
Advisory (SCA) level winds across PZZ673/676, with sub- advisory
winds across PZZ670. For Sunday through Monday, there will
be a 50-70% chance of SCA level winds across PZZ673/676. For
Tuesday through Thursday, high confidence in SCA level winds and
seas developing across all the Outer Waters with a 40-60% chance
of Gale force winds developing Wednesday and Thursday.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. Tonight through Monday, high
confidence in winds and seas remaining below SCA levels. For
Tuesday through Thursday, there is a 50-70% chance of SCA level
winds and seas.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. Tonight through Sunday, winds and
seas are generally expected to remain below SCA levels, but there
is a 60% chance of SCA level winds across the western half of the
Santa Barbara Channel during the afternoon and evening hours. For
Monday and Tuesday, there is a 60-80% chance of SCA level winds
(and a 30-50% chance of Gale force winds) across the western half
of the Santa Barbara Channel and a 20-40% chance of SCA level
winds across the rest of the southern Inner Waters. For Wednesday
and Thursday, high confidence in winds and seas remaining below
SCA for most of the southern waters except for a 20-30% chance of
SCA level winds across the western half of the Santa Barbara
Channel.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 650-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Gomberg/Cohen
AVIATION...Phillips
MARINE...RAT/RS
SYNOPSIS...Cohen

weather.gov/losangeles

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