Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/29/22

Area Forecast Discussion

National Weather Service Indianapolis IN

 1005 PM EST Mon Nov 28 2022

.Forecast Update...
Issued at 1005 PM EST Mon Nov 28 2022

Little change made to the late evening forecast update. Current
satellite imagery shows low stratus across all of Central Indiana
very slowly clearing from SW to NE. 03z IND ACARS sounding shows
strong dry air advection aloft with a strong inversion trapping
moisture from the surface to about 1 km agl. GOES Nighttime
Microphysics imagery shows dry air is slowly eroding the stratus
deck, so expect clouds to begin breaking up and lifting through the
overnight hours. Winds are still elevated at this hour around 4 to 6
kts at most sites, which should keep most areas free of fog. Would
not be surprised to see patchy fog in wind sheltered areas and in
the Wabash River valley later tonight and closer to sunrise.
However, confidence in fog developing is low enough to omit it from
the forecast for now. Will keep an eye on the fog potential tonight
though.

No changes made to the forecast for tomorrow as everything looks on
track. Strong low level jet developing, so expect southerly wind
gusts over 30 kts by late morning and persisting through the evening
hours. Despite mainly cloudy skies tomorrow, strong warm air
advection ahead of an approaching cold front will result in
temperatures spiking into the lower 60s region-wide. The front is
not expected to move through until the very early morning hours
Wednesday, so expect temperatures to remain elevated in the upper
50s to near 60 for much of tomorrow night. No changes in the
forecast regarding severe weather/thunderstorm potential. More
information on the storm threat can be found below in the long term
forecast section of the discussion.

&&

.Short Term...(This Evening through Tuesday)
Issued at 258 PM EST Mon Nov 28 2022

Tonight.

Upper level flow will begin to become more southwesterly ahead of a
rain producing system that will arrive Tuesday night with gradually
increasing surface flow through the overnight hours as the surface
pressure gradients increase. A weak near surface inversion will
limit the magnitude of winds during the overnight hours, but with a
LLJ of 30kts at 1000ft, expect that even with the unfavorable mixing
conditions that winds should occasionally gust to 15kts through
daybreak.  Skies will remain mostly cloudy which will help moderate
temperatures and combined with the increasing southerly flow, only
expecting lows to drop into the upper 30s to 40 tonight.

Tuesday.

Warmer than normal conditions expected for tomorrow ahead of the
showers and storms that are expected to pass through central Indiana
during the overnight hours.  Details on the storm threat will be
covered at the start of the long term section.  Wind speeds will
rapidly begin to increase by 10 AM as the near surface inversion
breaks and the 40kt jet at 900mb begins to mix down.  Near Wind
Advisory conditions are possible across the northwestern counties
towards the afternoon, especially if the expected clearing happens
between 11 AM and 3 PM.

The lower atmosphere will then quickly saturate again late in the
afternoon into the evening ahead of precipitation tomorrow night.
There will likely be a stray shower or two ahead of 7 PM, but think
that the bulk of precipitation will be later. With the abundant
southerly flow and likely clearing during the afternoon, have bumped
up highs into the low to mid 60s.

&&

.Long Term...(Tuesday Night through Monday)
Issued at 258 PM EST Mon Nov 28 2022

* Strong to Severe Storms Tuesday Night
* Gusty winds Tuesday Night into Wednesday
* Much Colder Midweek Then a Warming Trend for Late Week
* Unsettled Weather Returns This Weekend into Early Next Week

The main focus in the long term period will be on the high impact
storm system for Tuesday night and early Wednesday...bringing the
potential for more rain along with a threat for strong to severe
convection along and ahead of an intense cold front.

As mentioned in the short term discussion...strong wind gusts and a
rapid expansion of showers and a few storms will occur on Tuesday
afternoon and be ongoing by Tuesday evening. The primary surface
wave will be in the process of intensifying as it tracks through the
upper Midwest Tuesday evening and eventually lifts towards James Bay
by Wednesday morning. A rich sure of deep moisture will advect north
Tuesday afternoon and evening ahead of the cold front with
dewpoints surging into the mid and possibly upper 50s by the
evening.

As this system continues to evolve...the focus for significant
severe weather has been highlighted for the lower Mississippi Valley
for several days now with a higher uncertainty further north across
the Ohio Valley due to a lesser low level moisture...buoyancy and
instability presence. Despite that...the setup looks supportive of
at least an isolated risk for severe convection reaching up into
parts of the area by Tuesday evening with strong mid and upper level
diffluence over the region...combined with high levels of BL shear
and a 60+kt low level jet moving across the area. Climatology also
supports the potential risk with the top CIPS analog of the
12/23/2015 QLCS that produced wind damage and a few spin up
tornadoes across the forecast area. The timing with that event
though was during the mid and late afternoon whereas the highest
threat with this system will focus more during the evening and early
overnight. That being said...little instability is necessary in
these high shear/low CAPE environment where the dynamics and shear
will help drive the risks. And as has been mentioned in previous
discussions over the last day or so...the overnight timing will not
mitigate the overall risk for severe weather even with surface
instability largely being held south of the forecast area.

Breaking it down further...there now appear to be two periods of
interest within the broader timeframe from Tuesday evening through
the predawn hours Wednesday. During the evening...confidence
continues to grow in an increase in prefrontal convection expanding
north from the lower Mississippi and Tennessee Valleys. While
damaging winds will be a concern with any of the stronger
convection...a subtly elevated brief spin up tornado risk would
likely focus during the evening when 0-1km SRH values are enhanced
and hodographs show impressive turning through the lowest 2-3km.
This threat will largely diminish by 05Z or shortly after as the
stronger shear and SRH values shift east.

The focus will then shift to the second area of concern which will
be a thin broken convective line poised to pivot across the forecast
area with the cold front from west to east in the 06-09Z timeframe.
By this point...the concern shifts almost solely to damaging winds
along the line as the wind profile becomes more unidirectional and
the boundary layer inversion present earlier in the night largely
dissipates enabling any of the storms to mix down the stronger winds
aloft. A narrow axis of 0-3km CAPE values will develop in tandem
with the line and may even increase to levels above 100 j/kg as it
transitions across the forecast area. While the bulk of the low
level SRH has moved off to the east by this point...0-1km SRH values
of 50-100 m2/s2 linger which would be enough to support a few
mesovortices along the line. After 09Z...any severe risk is over
with the front east of the region.

To summarize the severe risks before we move on to the rest of the
long term...potential exists from the evening through the predawn
hours Wednesday. Damaging winds are the primary concern but
prefrontal convection during the evening may also carry a threat for
a few spin up tornadoes. QLCS style convective line then tracks
across the forecast area overnight with the winds the primary risk.
Also...little lightning and thunder may accompany the convection...a
common feature in the Ohio Valley with cool season nocturnal
convection within a high shear/low CAPE environment. Once the front
passes early Wednesday...temperatures will drop rapidly as intense
cold advection commences immediately. A few snowflakes may mix in as
well prior to the precipitation ending. Outside of convection...
winds will be gusty Tuesday night into Wednesday.

The remainder of the extended will shift to a proverbial roller
coaster as a sharply colder airmass in wake of the Tuesday night
storm system settles over the region for midweek...then shifts back
to a warmer regime by late week with a quasi-zonal flow pattern
aloft resuming. High pressure will track across the eastern part of
the country with dry weather Wednesday through Friday. Another
surface low will track across the upper Midwest Friday night into
Saturday morning but available moisture will be limited and only
expecting scattered showers at this point. After a brief return of
high pressure Saturday...the front will return north as a warm front
for the second half of the weekend into early next week and at least
at this early stage...appears to have the potential to produce an
extended period of much needed rainfall Sunday through next Tuesday
as surface waves ride along the boundary. There could be snow mixing
in at times initially early Sunday but once the lingering cooler
airmass gets pushed away to the north...rain is likely to be the
predominant precip type.

Highs Wednesday will likely hold in the mid and upper 30s behind the
strong cold front...but expect a recovery back into the 50s by
Friday and Saturday for parts of the region. Temperatures will
continue to fluctuate in the 40s and 50s Sunday and Monday and will
be dependent on the location of the frontal boundary.

&&

.Aviation...(00Z TAF Issuance)
Issued at 629 PM EST Mon Nov 28 2022

Impacts:

* Lingering MVFR cigs at all sites through the overnight hours

* Southerly wind gusts to 30kts after 15Z Tuesday

Discussion:

Low level moisture trapped under an inversion just above the surface
has resulted in MVFR cigs around 2000-2500 ft across all of Central
Indiana today. Expect MVFR cigs to remain through the overnight
hours, then lift around or just after sunrise Monday... especially
as winds pick up and mix out the stratus deck.

Strong southerly winds begin around 15z tomorrow morning and persist
through the day. Winds may gust over 30 kts at times, especially
during the afternoon and evening hours.


&&

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

$$

Update...CM
Short Term...White
Long Term...Ryan
Aviation...CM



Area Forecast Discussion

National Weather Service Louisville KY

 815 PM EST Mon Nov 28 2022

.Forecast Update...
Issued at 815 PM EST Mon Nov 28 2022

The lingering stratus deck is beginning to clear and erode from SW
to NE across the area at this hour. This will shut off any lingering
drizzle chances we had observed late afternoon/early evening, and
may provide some brief clearing. However, upper cloud cover is
already starting to overspread the region ahead of the next system,
so still expecting a mostly cloudy overnight. Otherwise, look for a
pretty quiet night with temps bottoming out in the upper 30s and low
40s across the area.

A tightening pressure gradient takes hold of the area by late
morning and will be looking at strong S to SSE surface winds between
15 and 25 mph, with gusts in the 25 to 35 mph range at times. Still
quite a bit of question on how much we are able to destabilize going
into the evening and overnight, which will ultimately drive just how
robust our severe threats will be. At the very least, it does appear
that a hail/wind threat will exist from early evening well into the
overnight, but tornado potential will depend on the erosion of a
near-surface inversion that will try to keep convection elevated.
Will continue monitoring the latest data heading into that event.

&&

.Short Term...(This evening through Tuesday)
Issued at 315 PM EST Mon Nov 28 2022

High pressure continues to build overhead and at the surface while
an expansive low layer of stratus persists across much of the OH
Valley. Current satellite does show some breaks in this layer, but
expect cloudy conditions to continue throughout the daylight hours.
AMDAR soundings out of SDF do show a weak drizzle signature, and
current radar is beginning to show very light returns across
southern Hardin County in to Larue; therefore will add mention of
patchy light drizzle until around midnight.

Overall flow will begin to shift from WSW to S overnight as the
fleeting ridge drifts eastward. This will result in H85 WAA, which
should serve to erode the stratus layer and give way to broken
cirrus. To our west, a deepening low pressure system will tighten
the pressure gradient over our area resulting in windy conditions
beginning tomorrow mid morning and increasing through the afternoon
into evening. Gusts of 25-35mph are likely.

Showers and thunderstorms will begin to enter our forecast area by
as early as 28/21Z according to the latest hi-res guidance. Shear
profiles will be conducive for potential damaging convective wind
gusts, but subtle low level stable layers will probably postpone any
severe weather until after sunset...more on the severe potential
below.

.Long Term...(Tuesday night through Monday)
Issued at 330 PM EST Mon Nov 28 2022

...Increasing Chances of Strong-to-Severe Storms Tue Night...

Deepening sfc low ejects out of the central Plains and towards the
Great Lakes, eventually bringing a cold front through the region by
Wednesday morning. A robust LLJ with pull plenty of Gulf moisture
northward into the lower and mid Mississippi River Valley and the
Ohio Valley, and should expect to see wind gusts possibly in the 30-
35mph range for Tuesday evening. This system will provide a
significant severe weather event for the southern US, which may
extend far enough north into portions of western and central KY.

As it usually goes around here, Tuesday night will feature a high
shear, low instability environment. Dewpoints creeping into the mid
to upper 50s will nose into central KY by Tuesday night, with south-
central Kentucky possibly reaching dewpoints in the low 60s. CSU
Machine Learning severe forecast probabilities continue to indicate
a wind and hail probs for our western forecast area, with a low-end
tornado threat. We`ll begin to see scattered showers and storms
associated with WAA regime track into the region by late afternoon
or early evening. A stout low level inversion should help limit any
instability to remain elevated, though steepening mid level lapse
rates suggest the possibility of some elevated hailers and spinners
for Tuesday night. Tons of shear will allow for organized elevated
convection, though any localized interactive from outflow boundaries
or cell mergers could result in some of that instability working
down closer to the sfc, which could result in a brief tornado to
occur. Overall, main threats for our area will be severe winds and
hail.

Model soundings generally agree on having the low level inversion
break down as we get closer to 09-11z Wed ahead of the cold front.
If we are able to become uncapped, could have a very narrow window
of sfc based instability for the cold front to work with. A final
line of showers and storms along the frontal boundary are expected
to pass through the region by 12z Wed. Though overall shear weakens
and become more unidirectional, still could have enough lingering
helicity to support some organized convection and maybe some
embedded spinners within the line before sunrise Wednesday.

Though we should have some efficient rainfall rates, and possible
training of cells, overall storm motions appear to be rather
progressive. Given the severe drought conditions in place, flooding
is not a major concern. OHRFC 1-hr flash flood guidance is around
1.5" across to the east of I-65, which could be low enough for some
nuisance flooding issues if we do see repeating rounds of heavy
rain rates.

In a post-frontal regime, strong cold air advection flow will result
in crashing temps through Wednesday. Max temps for the day are
expected earlier in the morning while under the influence of strong
WAA ahead of the front. Clouds will be moving out by the afternoon,
with the overnight period set to offer efficient radiative cooling
processes for Wednesday night. Combined with CAA, expect morning
lows to drop down into the low to mid 20s by Thursday morning.

A more zonal flow aloft with sfc high pressure scooting across the
Ohio Valley should help keep temps cooler than normal for Thursday.
Forecast highs for the day will be in the 40s. Sfc high will quickly
shift off to the east by Thursday night, and our area should be
reintroduced to warm southerly return flow for Friday. Another
shortwave should move across the CONUS by Friday and into Saturday,
which will provide our next precip chances into the weekend.

&&

.Aviation...(00Z TAF Issuance)
Issued at 650 PM EST Mon Nov 28 2022

Impacts: Retreating MVFR ceilings this evening, gusty winds Tuesday
afternoon, and storms late in the period.

Currently seeing some ceilings right around the high MVFR/low VFR
threshold. Do expect continued improvement toward Midnight, and
reflected this in forecast timing back to VFR for LEX/HNB.
Otherwise, stayed optimistic for BWG/SDF to hold low VFR conditions.

After a quiet overnight, look for surface winds to ramp up out of
the SSE around 15 to 25 mph, gusting between 25 to 35 mph at times.
As we move into the evening hours, chances for showers and storms
will increase, along with chances for scattered thunderstorms.
Timing is fairly low confidence, but put in a reasonable time frame
of impacts for now.

Confidence: High for ceilings and winds, low to medium for t-storm
timing.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...BJS
Short Term...CG
Long Term...CJP
Aviation...BJS