Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/15/22

Area Forecast Discussion

National Weather Service Indianapolis IN

 1201 AM EDT Sat Oct 15 2022

...Updated Aviation Discussion...

.Forecast Update...
Issued at 936 PM EDT Fri Oct 14 2022

No major changes needed with the ongoing forecast as conditions are
generally evolving as expected.  The area of rain over central
Illinois associated with the approaching trough will arrive in the
northwestern counties after 10 PM with a few hundredths of an inch
of rain for those counties through 2 AM.  The primary concern with
these showers will be the potential for stronger wind gusts as the
rain helps bring down the 40kt winds at cloud level.  We`ve already
seen a few gusts to 30kts ahead of the rainfall at LAF and FKR but
as the temperatures continue to cool, the frequency of the stronger
gusts will gradually decrease.  Latest ACARs soundings show a
minimal amount of elevated instability with these showers, so can`t
rule out a few pieces of graupel in the stronger showers.

Lows in the mid to upper 30s across the northwestern counties still
looks probable, but will be dependent on how quickly the clouds
begin to clear in the aftermath of rainfall. Will monitor these
conditions through the night and make adjustments as needed.

&&

.Short Term...(This evening through Saturday)
Issued at 226 PM EDT Fri Oct 14 2022

* Critical Fire Weather conditions this afternoon
* Gusty winds 35 to 45 mph
* Showers possible this evening with gusty winds

Today

Temperatures across the region have warmed into the upper 50s to
near 60 as of 2pm. Excellent boundary layer mixing to as high as
700mb has allowed for efficient downward transfer of momentum aloft.
Low-level flow within the 925 to 700 mb layer is around 30 kts,
based on soundings out of ILX. Winds at the surface have been
gusting consistently to around 25 kts at IND late this morning and
early this afternoon. A potent shortwave trough is modeled to reach
Indiana by around 8pm this evening, and in the process gain a
negative tilt. Winds in the aforementioned layer should increase as
this feature closes in, with 850mb flow increasing to 40kts and
700mb flow to around 60kts. Therefore, wind gusts should gradually
increase through the afternoon before tapering off as solar
insolation is lost and stability returns. Gusts could top out around
35kts for most locations before the day is out.

Additionally, very dry air in the lower levels is mixing down to the
surface. Dew points at IND are already in the upper teens, with RH
values around 16 percent as of 2pm. Skies have been trending clearer
than forecast, so the lower end of guidance regarding RH is
preferred for the remainder of this afternoon. Continued mixing
should lead to RH values dropping to as low as 15 percent in places.
The very dry and cloud-free air and deep mixing should allow high
temperatures to reach their full potential this afternoon, which
would generally be in the mid to upper 60s based on nearby soundings.

The combination of dry and windy weather will lead to critical fire
conditions today. Recent lack of significant rainfall has lead to
low fuel moisture levels, currently between 7 to 10 percent as of
yesterday. Any fires that manage to ignite today will have little
issue spreading, so the Red Flag Warning issued previously is
maintained through 8pm.

Tonight

The potent shortwave arrives this evening, with increasing clouds
and potentially a few showers. As mentioned before, the low levels
are very dry, so widespread rainfall is not anticipated. But strong
positive vorticity advection and diffluence aloft will lead to an
enhanced area of lift as the system moves through. Additionally,
some weak CAPE around 100 J/kg at the top of the mixed layer may
enhance the convective nature of any showers this evening. In fact,
some of the CAMs, namely the HRRR and 3km NAM, depict a more
cellular appearance to the shower activity this evening. Model
soundings indicate that any convective elements would be rather
shallow, as a broad cap resides around 600mb. Nevertheless, strong
low-level flow as mentioned earlier could easily be brought to the
surface within the stronger showers. Therefore, wouldn`t be
surprised to see some non-severe gusty winds associated with shower
activity later on. The best chance would be north of a Terre Haute
to Indianapolis line, which is closer to the best dynamics ahead of
the approaching shortwave. The synoptically driven wind should die
down quickly as daytime heating is lost, as it is primarily driven
by surface mixing. Wind associated with the showers could persist a
bit longer, however.

As the system departs, skies should gradually clear throughout the
night. Large scale troughing over the Great Lakes is maintaining a
cooler air mass aloft, which should allow for a rather chilly
overnight if ideal radiational cooling conditions materialize. Weak
surface CAA / a cold front behind the shortwave will aid in cooling
potential overnight. The most likely locations for maximized cooling
would be the northwestern part of the CWA, which is deeper into the
post-front air mass and will see clearing earlier compared to places
further south. Lows should dip into the mid 30s across our north,
but only into the low 40s south of Indianapolis. Patchy frost is
possible, but dry low-levels and a residual breeze should prevent it
from being too widespread.

Tomorrow

Benign weather is anticipated to start the weekend, at least
compared to today`s weather. Surface high pressure will be in
control, and light winds along with mainly clear skies should
prevail. An area of high clouds may arrive mid afternoon as a weak
wave aloft slides in from the west. High temps are expected to be
cooler than today, but not significantly so.

&&

.Long Term...(Saturday night through Friday)
Issued at 226 PM EDT Fri Oct 14 2022

Significant Weather Highlights:

* Widespread freeze conditions likely multiple mornings early-mid
  next week

* Hard freeze possible, which would officially end growing season

A fairly stagnant upper level pattern is expected much of the long
term period, featuring a western CONUS ridge/Rex block and eastern
CONUS trough/closed upper level low.

This will lead to mainly dry conditions, with much below normal
temperatures expected for at least a significant portion of the
period, particularly the early to middle portion of the coming work
week.

A dry cold front will move through the area late Sunday, followed by
a blast of cold air accompanying a strong surface high pressure
system driven southward in the highly amplified flow by a nearly
meridional polar jet stream. The overall cyclonic flow aloft will
allow some lake effect clouds and perhaps a low chance for light
precipitation to nudge into northern/northeastern portions of
central Indiana late Monday into Tuesday, but the larger story will
be the anomalously low temperatures, which look nearly certain to
deliver widespread freeze conditions one or more nights next week,
with a hard freeze not out of the question (which would officially
end the growing season and frost/freeze headlines for the area).

Ensemble data suggest that Tuesday night should be the coldest
period, with temperatures quite cool about 24 hours either side of
this time, and suspect that blend may be underselling the degree of
the cold expected. Will be trending temperatures, especially lows,
toward the low end of the guidance envelope as a result. Lake effect
could complicate this in the north/northeast, but these
uncertainties will come into clearer view with time. Nonetheless,
well below normal temperatures will dominate much of the long term
period, with some moderation in temperatures expected very late in
the period.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1201 AM EDT Sat Oct 15 2022

Impacts:

- VFR Conditions are expected this TAF period.

Discussion:

A cold front quickly moving across the TAF sites will quickly exit
the area within 1-2 hours after 06Z. GOES16 shows mainly mid level
cloud across the region with this feature. These VFR clouds will
quickly exit to the east overnight as the front departs and high
pressure centered over IA/NB begins to push into IL and IN.

Although cyclonic flow is expected to remain in place aloft
overnight and the rest of Saturday, the surface high pressure to the
west will continue to build across Indiana. Forecast soundings show
a very dry column through the rest of the period with unreachable
convective temperatures. Thus continued VFR conditions.

&&

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

$$

Update...White
Short Term...Eckhoff
Long Term...Nield
Aviation...Puma



Area Forecast Discussion

National Weather Service Louisville KY

 932 PM EDT Fri Oct 14 2022

.Forecast Update...
Issued at 930 PM EDT Fri Oct 14 2022

Minor update to refresh the grids and confirm that the Red Flag
Warning expired at 15/00Z. Increasing cloudiness tonight ahead and
along the approaching cold will limit radiational cooling while the
front itself will not bring PoPs to the area owing to low-level dry
air. On the other hand, attendant strong LLJ will maintain gusty
winds overnight. Forecast for tomorrow looks on track with a low
possibility of light showers along the Tennessee border if
isentropic lifting and steep mid-level lapse rates can overcome the
surface dryness.

&&

.Short Term...(Tonight through Saturday evening)
Issued at 325 PM EDT Fri Oct 14 2022

Across the region this afternoon, very dry and breezy conditions are
being observed with dewpoint depressions approaching 50 degrees
across central KY and southern IN. As a result of these dry and
breezy conditions, increased fire danger is prevalent through the
remainder of the afternoon with fire weather headlines prevailing
through 00Z, at which point RH values will begin to recover
somewhat. Current water vapor imagery shows broad troughing centered
over the Mississippi Valley, with shortwave disturbances pivoting
along the periphery of the large-scale wave. A mid-level shortwave
located over Iowa at this hour will have an associated cold front
that will swing across the Midwest and lower Great Lakes tonight
into tomorrow morning. This front looks to be fairly moisture-
starved, with no precipitation expected as the front passes through
overnight. Ahead of the front, winds will back from SW this
afternoon to southerly overnight, before veering again to W/SW with
FROPA tomorrow morning.

On Saturday, the cold front is expected to slow as it pushes into
extreme southern KY and central TN. As it becomes nearly stationary,
high-res guidance is showing that increased moisture advection along
the front could promote a few showers near the TN border during the
afternoon hours. On the other hand, any increase in mid-level
moisture will have to overcome a dry layer below 850-mb, and overall
rain chances should still be pretty low. Will go with slight chance
PoPs mainly along and south of the Cumberland Parkway, with very
little if any QPF. Temperatures on Saturday will vary from north to
south with the positioning of the front: expect mid-60s for highs
across southern IN, highs around 70 across north central KY and
highs in the low-to-mid 70s across southern KY.

&&

.Long Term...(After midnight Saturday night through Friday)
Issued at 248 PM EDT Fri Oct 14 2022

Mostly dry conditions anticipated for Saturday evening, but moisture
will steadily move into southern portions of the region through
Sunday morning and eventually give way to rain showers. Much of this
rain will form in response to modest isentropic lift along ~300K
surfaces ahead of a cold front, with the greatest moisture depth in
the column generally across Tennessee and southern Kentucky. Rain
will likely arrive Sunday morning and gradually taper off from west
to east Sunday evening. Overall amounts vary depending on where the
rain bands set up, but thinking most spots will see under a quarter
inch, with a few `lucky` areas or swaths perhaps seeing closer to a
half inch.

Conditions will turn much drier and colder behind the front, as
average high temperatures (low 50s) from early to mid-week could be
as much as 20 degrees below climo values (low 70s). Overnight lows
will feature below freezing temperatures for nearly the entire
region, with the coldest morning likely occurring Wednesday as
surface high pressure slides off just to our west. Wednesday morning
temps as of writing this are currently forecast to be in the mid to
upper 20s for all except the Louisville metro area, and a freeze of
this magnitude should end the growing season for the year.

As the surface high drifts to the south and east of the region
Thursday, southerly return flow will kick in across southern Indiana
and central Kentucky, and we`ll see a gradual warm up in
temperatures to end the week. Unfortunately, rain chances will be
extremely slim to end the week, so those who do not see rain over
this upcoming weekend will likely have to wait close to another week
before additional rain chances arrive.

&&

.Aviation...(00Z TAF Issuance)
Issued at 725 PM EDT Fri Oct 14 2022

Impacts/Confidence:

- High Confidence on LLWS tonight.

Discussion...VFR conditions will continue during this cycle. Surface
observations are already indicating winds slowing down as they turn
a few degrees to the south. As previously mentioned, cold front is
approaching the area from the west accompanied by a medium-level
cloud deck. Although radar imagery shows weak reflectivity, decided
to leave the fcst dry given a sufficiently deep dry airmass below
700-mb, as shown by an earlier AMDAR sounding from SDF. The most
prominent impact will be LLWS and the resultant air speed loss/gain
of 20 kts or more below 2,000 ft. Expect the strong LLJ to depart
the area before sunrise just as the front moves east of the
terminals. Winds will stay breeze and out of the west-southwest on
Saturday.

&&

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

$$

Update...ALL
Short Term...CSG
Long Term...DM
Aviation...ALL