Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/11/21

Area Forecast Discussion

National Weather Service Louisville KY

 1015 PM EDT Tue Aug 10 2021

.Forecast Update...
Issued at 1015 PM EDT Tue Aug 10 2021

Southern Indiana and central Kentucky are having a quiet but warm
and muggy evening. Temperatures are still around 80 with dew points
in the middle 70s and very little in the way of cooling breezes.

The question for the overnight hours and into early Wednesday
morning is if renewed convection will develop. Powerful
thunderstorms have been charging across Wisconsin and northern
Illinois and are now about to enter Lower Michigan after having
traversed Lake Michigan (will be interesting to see if a seiche can
develop). These storms will remain to our north ahead of a 5H
shortwave trough just behind the line of storms.

However, as we go into the late night and early morning hours, a
250mb jet streak will briefly intensify from Iowa into Wisconsin,
and a 500mb speed max will travel from Iowa into northcentral
Illinois. A low level jet will increase from the mid-Missouri
Valley to the western Great Lakes. These features will interact with
a very moist and unstable atmosphere. There may also be some outflow
boundaries left over from the earlier convection to the north. As a
result, scattered storms may develop across central Illinois and
progress into Indiana overnight. The best chance for any stronger
storms should be just to our north closer to better forcing. Deep
layer shear isn`t strong but will be enough to support convection.
As the storms approach southern Indiana and possibly north central
Kentucky by morning they should be slightly isolated and moving away
from the best support not to mention arriving at a climatologically
unfavorable time of day for strong storms.

Confidence in all this coming together is not particularly high and
the best coverage of any storms that do develop should be just to
our northwest and north, so in the forecast will hold onto the
possibility of storms but will restrict that possibility to chance
(which is what the previous shift had as well).

&&

.Short Term...(This evening through Wednesday)
Issued at 315 PM EDT Tue Aug 10 2021

Current water vapor imagery shows the upper level trough moving east
of the Mitten State while radar shows associated convection along a
surface convergent boundary moving east of our CWA. Scattered
afternoon cu field has blossomed in the wake of the boundary, but a
slight chance of pop up showers and storms continues to exist this
afternoon into early evening. Latest mesoanalysis shows ample CAPE
with values up to 4000 J/kg accompanied by a moisture-rich
environment (PWATs around 2.00 inches). Low shear environment
continues to suggest lack of storm organization with pulse storm
modes capable of locally torrential rain, gusty winds, and cloud to
ground lightning. Working against convective potential, AMDAR
soundings out of SDF reveal near moist-adiabatic mid-level lapse
rates that should temper upward storm growth. With that said, will
continue a slight chance mention throughout the evening.

Temperatures this afternoon increased into the upper 80s to low 90s
west of I-65, where dew points have also reached into the mid to
upper 70s. This has resulted in heat indices in the low 100s. Have
issued an SPS for elevated heat indices for these areas until 8pm
EST.

Overnight, hi-res models agree on a couple of waves of convection
moving into southern Indiana and central KY. The first wave appears
to entering our NW counties around midnight and weaken as it
progresses eastward. The second looks to arrive around sunrise. But
hi-res models have struggled with recent scenarios, so confidence is
low in exact timing and spatial extent of these waves of convection.

Expect mild lows with temperatures only falling into the low to mid
70s. Wednesday will be another hot and muggy day with another chance
of afternoon showers and storms. Wednesday max temps will reach into
the low to mid 90s with dew points in the mid 70s, resulting in heat
indices in the 100s. After collaboration with surrounding WFOs, will
go ahead and issue a Heat Advisory for Wednesday and Thursday
afternoons mainly for areas west of the I-65 corridor.

.Long Term...(Wednesday night through Tuesday)
Issued at 310 PM EDT Tue Aug 10 2021

At the start of the extended period, expect to find broad upper
trough over central Canada, with the main belt of westerlies to our
north as the base of the trough pushes through the Upper
Midwest/Great Lakes region. To our south, expansive area of high
pressure will extend across the Southeast, placing the region in
deep southwesterly flow. As warm and moist air continues to pump
into the area, expect Thursday to be similar to Wednesday with high
temperatures topping out in the lower to mid 90s. Heat indices will
exceed 100 degrees for most locations, with the best chances of
seeing indices above 105 degrees being along and west of I-65. Will
go ahead and hoist a Heat Advisory for Thursday to highlight this.
To go along with this, model guidance has been showing a decreasing
trend for PoPS on Thursday, instead favoring a slightly stronger
southern ridge helping to keep us mostly dry. However, an isolated
shower or storm cannot be ruled out.

Friday looks to be the last day with temperatures above
climatological normals as a cold front is then expected to approach
and move through the area Friday afternoon into Saturday. Ahead of
the front, afternoon highs are still progged to top out in the lower
to mid 90s on Friday. Precip chances will then increase during the
afternoon and evening hours and continue into Saturday as the cold
front pushes through. Uncertainty then increases for the end of the
period as models struggle to agree on how far south the frontal
boundary pushes. Therefore will carry slight chance to chance PoPs
mainly during the afternoon and evening hours for Sunday and Monday.
Temperatures will return to around/below normals for the weekend and
into early next week with highs topping out in the mid to upper 80s
and lows in the 60s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 727 PM EDT Tue Aug 10 2021

A small complex of thunderstorms will impact HNB at the start of the
TAF period but should last less than an hour. The gust front out
ahead of these storms may make it to SDF, but if it does it will be
in a weakened state and probably with little associated thunder.
Will keep an eye on it as it presses eastward.

After several quiet hours late this evening, thunderstorms are
expected to develop over Illinois and head to the east and southeast
late tonight, possibly affecting the northern TAF sites early
Wednesday morning. Confidence in this is not particularly high so
will stick with a PROB30.

Widely scattered thunderstorm development will be possible again
tomorrow afternoon, but should be sparse enough to leave out of the
TAFs for now. Future forecast issuances can address this further
especially after seeing whether or not we get morning convection.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory from 1 PM EDT /noon CDT/ to 9 PM EDT /8 PM CDT/
     Wednesday for INZ076-077-083-084-089>092.

     Heat Advisory from 1 PM EDT /noon CDT/ to 9 PM EDT /8 PM CDT/
     Thursday for INZ076-077-083-084-089>092.

KY...Heat Advisory from 1 PM EDT /noon CDT/ to 9 PM EDT /8 PM CDT/
     Wednesday for KYZ023>030-061>063-070>075.

     Heat Advisory from 1 PM EDT /noon CDT/ to 9 PM EDT /8 PM CDT/
     Thursday for KYZ023>030-061>063-070>075.

&&

$$

Update...13
Short Term...CG
Long Term...JML
Aviation...13