Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/30/21

Area Forecast Discussion

National Weather Service Louisville KY

 1113 PM EDT Thu Jul 29 2021

.Mesoscale Update...
Issued at 1111 PM EDT Thu Jul 29 2021

Isolated to scattered thunderstorms have filtered into our southern
Indiana and Kentucky Bluegrass counties and are approaching the Ohio
River. Activity thus far has remained sub-severe, though one storm
currently along the Orange/Harrison (IN) county line has shown
supercellular characteristics and has been watched closely.

Activity over the next hour or so will likely remain isolated to
scattered, but we could see some additional storms drift in from the
north overnight along the cold front. The overall strength of the
convection overnight still has the potential to become severe given
some favorable instability and modest shear in place, but at least
up to this point weak capping in the low levels has kept things from
getting too out of control.

Issued at 920 PM EDT Thu Jul 29 2021

Isolated to scattered storms are starting to develop or enter into
our southern Indiana counties. Most of this activity has been non-
severe, but toward Crawford County, Illinois, there was a supercell
that produced a TDS via KVWX. The environment across our southern
Indiana counties remains very unstable above a weak inversion (>4000
J/KG MUCAPE), so if/when storms can overcome it and tap into the
unstable air, they could quickly become strong or severe.

Earlier in the day, models hinted at broken lines of strong to
severe storms pushing into our region during the overnight hours.
The latest HRRR runs indicate much of this activity may stay
isolated to scattered in nature for the majority of the night, and
given the latest radar trends, think this could be a viable
solution. Severe potential also looks like it could persist a bit
longer than originally thought and affect portions of south-central
Kentucky through 08z-09z. One concern with more discrete activity
overnight would be a lesser threat for severe wind potential and a
higher threat for large hail and isolated tornadoes in supercells.
Thankfully, deep layer and low level shear weaken as you go toward
southern Kentucky, so the highest threats for severe potential
continue to be across southern Indiana and northern/central Kentucky.

Issued at 658 PM EDT Thu Jul 29 2021

AMDAR soundings within the past hour have indicated a weakening of
the cap in the 900-800mb layer with winds now taking on a more
northwesterly component. KLVX has also detected a couple of rogue
cells that developed, though they have struggled to strengthen given
the weak capping still in place. This activity is not anticipated to
become strong or severe.

Over the next hour or so, we may continue to see an occasional rogue
cell go up across southern Indiana and central Kentucky. Activity
currently in central Illinois and Indiana along a weak surface
boundary will begin drifting into our southern Indiana CWA counties
between 00-01z. Additional activity along a cold front just to its
north will filter into the region around or after 03z. Strong to
severe storms will be possible with that activity as it drifts
southward.

Issued at 515 PM EDT Thu Jul 29 2021

Recent AMDAR soundings from SDF indicate a fairly impressive cap
remains in place (~23C near 800mb). A look at SPC mesoanalysis pages
and high-res model guidance of 900-800mb fields indicate a warm
`nose` of temperatures stretching from the central Plains into the
lower Ohio Valley resulting in the strong cap. Winds currently at
these levels are generally out of the west or west-northwest, so
temperatures in these levels should not change much in the very near
term, which means the cap should stay in place and prohibit storm
development.

It`s not until we get closer to 00z that we begin to see winds in
these levels shift more northwesterly as a trough sinks in from the
north. Cooler temperatures aloft associated with the trough will
advect in and help to break down and weaken the cap. Convection
currently in central Indiana and Illinois will drift close or toward
our area over the next several hours, and depending on how organized
it is and if there are any outflow boundaries or cold pools
associated with convection, it could be enough to overcome a
weakened cap. Threat for strong to severe storms will likely occur
after 00z and persist into the early morning hours.

&&

.Short Term...(This evening through Friday)
Issued at 320 PM EDT Thu Jul 29 2021

...Strong to Severe Storms Possible this Evening...

So far this afternoon temperatures have warmed into the upper 80s
and low 90s as of 2 pm EDT. Dew points were just oppressive in the
mid/upper 70s. This was producing heat indices around 100 degrees,
mostly west and along I-65 where we have the higher dew point
values. This heat and moisture has created a very unstable
atmosphere which will remain in place as we go into the evening
setting the stage for the development of strong to severe storms.
The Storm Prediction Center continues to keep the northern third of
our CWA (county warning area) in a slight risk for severe
thunderstorms. The main threat being gusty damaging winds and
torrential heavy rain.

Afternoon mesoanalysis shows sfc cold front stretching across
northern MO into northern IN over Lake Erie. Radar was showing
scattered development just south and along the boundary. South of the
front was strong to moderate instability with CAPE values across
central KY and southern IN ranging from 2500-3500 J/kg east of I-65
to 3500-4500 J/kg to the west. Model soundings were showing dry air
aloft keeping our DCAPE between 800-1000 J/kg keeping the main
threat gusty damaging winds in the strongest storms this evening.

Current hi-res model guidance is showing a slower solution in the
development of scattered to broken convection this evening. Updated
timing looks to drop a broken to scattered line of storms southward
into our southern Indiana and north-central Kentucky counties
between 9 PM- Midnight EDT and pushing southward into southern KY in
the early morning hours. As the storms work to along and south of
the Parkway, guidance has been consistent in showing the activity to
diminish as it reaches the TN/KY border by day break.

Tomorrow will feature cooler and less humid weather for the end of
the week. Dew points will fall into the low/mid 60s by the afternoon
with afternoon temperatures in the low to mid 80s north of the
parkways and mid/upper 80s south.

.Long Term...(Friday night through Thursday)
Issued at 315 PM EDT Thu Jul 29 2021

The long term forecast will see only minor changes.

On Saturday, as a shortwave/cold front drops south, trying to
amplify the trough over the eastern CONUS, a few showers and
thunderstorms will be possible. With most of the available moisture
towards the CWA`s southwest, believe the best chances of
precipitation will be on the southwestern side of the CWA Saturday
night before fading Sunday. Rainfall totals are expected to range
from a hundreth of an inch in our southeastern Indiana and
northeastern Kentucky counties to around three quarters of an inch
near Bowling Green. Some isolated areas could see higher
amounts under heavy downpours.

Moving into early next week, northwest flow with surface high
pressure remains over the CWA. This will suppress moisture to the
south and drop dew points into the 50s across the CWA by Tuesday.
With this pattern and lack of available moisture, believe mostly dry
conditions will prevail through the end of the work week.

However, the GFS does try to form an upper closed low over the
region on Wednesday. This would increase precipitation chances
towards the end of the week, but for now, don`t believe this is
likely. Plans should be based on a mostly dry comfortable week with
highs in the 80s and low dew points.

&&

.Aviation...(00Z TAF Issuance)
Issued at 659 PM EDT Thu Jul 29 2021

A broken line of showers and thunderstorms are may develop tonight
ahead of a cold front and push through southern Indiana and central
Kentucky. If a storm impacts a terminal site, expect gusty winds and
briefly reduced visibilities and ceilings. Drier air will filter in
behind the front and winds will turn to the north. VFR conditions
are anticipated in the wake of the storms for the remainder of the
forecast period.


&&

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

$$

Mesoscale...DM
Short Term...BTN
Long Term...KDW
Aviation...DM