Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/25/23

Area Forecast Discussion

National Weather Service Louisville KY

 717 PM EDT Mon Jul 24 2023

...Updated Aviation Discussion...

.Mesoscale Update...
Issued at 521 PM EDT Mon Jul 24 2023

After coordination with SPC, have decided to expand the Severe
Thunderstorm Watch into southern Kentucky. A line of robust
convection has developed in a corridor of enhanced precipitable
water values from just east of Evansville to around the Land Between
the Lakes. Though the storms in the LMK CWA so far have struggled to
become severe, there have been isolated instances of severe weather
with the western Kentucky storms, and current storms northwest of
Hopkinsville are posing a downburst threat. Although deep layer
shear is very weak over central Kentucky, there`s plenty of moisture
and instability. DCAPE is above 1000 J/kg with a microburst
composite above 5. It`s not a slam dunk given the weak shear and the
behavior of storms in central Kentucky up to this point, but with
the line of strong to severe storms approaching from the west, went
ahead and expanded the watch.

Issued at 345 PM EDT Mon Jul 24 2023

Storms have started to fire off along or near mesoscale boundaries
and are moving into the region. After coordination with SPC, Severe
Thunderstorm Watch #545 has been issued and covers portions of
southern Indiana and central Kentucky. South-central Kentucky
counties will be monitored for a potential watch expansion if
convection in western Kentucky remains strong as it moves toward our
region. The watch is expected to run through 10pm EDT.

&&

.Short Term...(This afternoon through tonight)
Issued at 234 PM EDT Mon Jul 24 2023

...Scattered Strong to Severe Storms Through Tonight...

Some active weather is expected through the remainder of the
afternoon into the first half of the overnight hours. Those with
keen eyes may note an area of weak surface low pressure associated
with an embedded but subtle upper level wave spinning near the
central IL/IN borders at this hour (1830z). This is evident not only
in surface observations but also in the low-level cu field when
satellite imagery is looped/animated. A couple of mesoscale
boundaries associated with or just ahead of the surface low pressure
are either near or moving into the region, and will serve as foci
points for convective development. AMDAR soundings from SDF at this
time (1830z) show a subtle cap near 900mb that has inhibited deeper
convective growth; once this cap erodes, though, plenty of
instability is in the atmosphere to fuel thunderstorm growth and
potential severity.

On the topic of severity, it appears the most likely threat with
scattered strong/severe storms today will be damaging wind gusts.
Deep layer shear will be weak to marginal (20-25kts), so storm modes
will be mainly in the form of pulse-like storms or weak multi-
cellular clusters. Steep low level lapse rates combined with high
DCAPEs (+1000 J/KG) support gusty or damaging wind gusts (in the
strongest storms) when their core collapses. Low level shear is very
weak and not supportive of a tornado threat. Additionally, the hail
threat will be limited by the lack of individual storm longevity;
pulse like storms will likely not be able to keep hailstones
suspended long enough to support anything more than sub-severe to
occasionally marginally severe hail today. Current SPC Outlook
highlights the wind threat as our most likely threat, which makes
sense given the current parameters and setup.

In terms of timing... with the 900mb cap nearly eroded, expect
storms to begin firing off between 20-22z. The threat for storms
will continue into the overnight hours, potentially persisting past
midnight. The best chances for any strong/severe storms will likely
be in the 21z (5pm EDT) through 03z (11pm EDT) timeframe. Not all
the storms that fire off today will be strong/severe, but there
could be several that produce gusty sub-severe (~40mph) to
marginally severe (~60mph) gusts.

Tomorrow is shaping up to be another warm day with isolated storm
potential. Unlike today, it does not appear there will be a well
defined lifting mechanism for convective development, so most
activity that develops tomorrow should remain isolated in coverage
(~20%) and confined to subtle mesoscale boundaries driven by terrain
or weak wind shifts.

.Long Term...(Tuesday through Sunday)
Issued at 245 PM EDT Mon Jul 24 2023

---------------------------------------------------------------------
Key Messages:

- Overnight Wednesday strong to severe storms possible in Southern
Indiana.

- Warming temperatures through the end of this week and heat indices
near 100.

- Frontal system will increase chance of precip this weekend.
---------------------------------------------------------------------

Synoptic Overview... Currently there is broad upper-level troughing
the in the eastern US and broad riding in the western US. Over the
next few days, the troughing will begin to flatten while the ridge
becomes stronger and tilts eastward. Generally, this will increase
temperatures in the region over the next several days. The Ohio
River Valley region will be situated on the northeastern periphery
of the ridge axis. This will allow shortwave troughs embedded within
the ridge to move into the region over the next several days.

Tuesday Night - Wednesday Night... Tuesday night, the region will be
under ridging which will allow dry, mostly clear, and warmer weather
to persist. Low temperatures Wednesday morning are expected to be in
the low 70s.

A shortwave trough on the northeastern periphery of the upper-level
ridge will deepen and move through the Midwest and Ohio River Valley
region Wednesday through Thursday. The upper-level low will likely
move over the Great Lakes region overnight on Wednesday. Warm
advection and a 40-45 kt LLJ will build in from the southwest as the
low approaches. Currently, models show that the edge of the LLJ will
brush the Ohio River. The best environment will be north of the Ohio
River for strong to severe storms. Main concerns with these storms
would be large hail and damaging winds. These storms will likely
remain north of our Southern Indiana counties, however, isolated-
scattered chances will remain in the grids.

Thursday - Friday... As the remnant showers and storms from the
overnight period move off to the east, the region will clear out.
Low temperatures will likely be in the low-mid 70s, high
temperatures in the low-mid 90s, and an afternoon breeze out of the
southwest. Thursday and Friday, we should remain dry with the upper-
level ridge impacting the region, however, I wouldn`t completely
rule out a shower or storm in the northern portion of the region on
both of these days.

Saturday - Monday... A shortwave trough will deepen on the northern
periphery of the ridge and move into the Midwest and Ohio River
Valley. Low-level southwesterly flow will increase moisture and
accompanied with a decent LLJ, we could see some showers and storms
in the region overnight Friday and overnight Saturday. On Sunday and
into Monday, the surface cold front should move through the region
and bring high temperatures back down into the upper 80s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 717 PM EDT Mon Jul 24 2023

Storms have slowly started to show a general weakening trend and are
progressing to the east. Will still have to deal with them for the
first couple hours of the TAF period, but then a quiet night will
follow with clear skies and light winds. Did go ahead and throw some
sunrise BR into the HNB TAF since they had rain earlier and are fog-
prone.

Winds should remain fairly light tomorrow with VFR conditions. Can`t
rule out an isolated afternoon storm or two, but threat isn`t
significant enough for inclusion in the far hours of the TAF.

&&

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

$$

Mesoscale...13/DM
Short Term...DM
Long Term...SRM
Aviation...13