Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/09/21

Area Forecast Discussion...UPDATED

National Weather Service Louisville KY

 906 PM EDT Sun Aug 8 2021

.Forecast Update...
Corrected at 906 PM EDT Sun Aug 8 2021

Upper and mid-level shortwave trough is moving ENE over the Upper
and Mid-Mississippi Valley this evening. Diurnal cu has all but
dissipated, but we do have a thin film of cirrus spreading in ahead
of convection off to the west. A north-south oriented squall line
has been pushed east across Illinois and southeastern Missouri.
Recent IR satellite trends show considerable cloud top warming in
central Illinois, but deep convection continues at the south end of
the line in Missouri. This area continues to be fed from the
southwest with higher theta-e air.

The environment downstream in Indiana and central Kentucky does not
support maintenance of the line. The 00z Nashville sounding
continues to show a modest warm nose between 700-500 mb and a huge
amount of dry air. PWATS drop off to around 1.4 inches near and east
of the Wabash Valley. CAPE is relatively weak as well, and some
SBCIN is already developing with the development of a nocturnal
inversion. By 04z, the RAP shows much stronger CIN. 04z is when the
weakening line should arrive in the far western CWA. Based on latest
radar trends, the HRRR looks too slow bringing the line into the
CWA. But the HRRR does show considerable weakening, which is
expected, as the showers and perhaps some storms push across the
western half of the forecast area between 04-08z. The much stronger
southern part of the line has the best chance to bring storms into
the CWA in our western and southwestern-most counties in KY.

&&

.Short Term...(This evening through Monday)
Issued at 300 PM EDT Sun Aug 8 2021

A healthy cu field exists this afternoon over the region looking at
vis satellite imagery.  A few small showers have tried to get going
but a robust mid level cap and dry layer (depicted in AMDAR
soundings) have kept convective development at bay for the most
part.  Very isolated locations may see a brief sprinkle or shower
through this evening but most will stay dry.

Tonight a mid level shortwave will approach the region bringing sct-
numerous showers/storms to the area late (after 4am). Convection
will spread east through the morning hrs providing rainfall to most
especially along and west of I-65. As the shortwave continues to
move through the region Monday afternoon, convection may continue or
redevelop over southern Indiana/central KY with some strong to
marginally severe storms possible. Soundings indicate CAPE values in
the 2000-3000 j/kg range with steep low level lapse rates and modest
0-6 km bulk shear in the 25-30 kt range.  Precipitable water
values will rise to near 2 inches which is well above normal.
Altogether these parameters would indicate the potential for strong
to damaging wind gusts, hail and heavy downpours in some of the
strongest storms Monday afternoon/evening.

Temperatures for tonight will hang in the upper 60s/lower 70s for
lows. Monday`s highs will be somewhat dependent on placement/timing
of showers/storms but should range through the mid to upper 80s.

.Long Term...(Monday night through Sunday)
Issued at 245 PM EDT Sun Aug 8 2021

Chance of showers and storms will continue into Monday evening and
through the overnight hours into Tuesday morning. An upper level
trough will likely spawn convection upstream across the Mid and
Upper MS Valley during the day Monday, which will have potential to
continue eastward into our CWA where CAPE/shear gradients exist. As
a result, our western counties are under a Day 2 Marginal Risk for
severe weather with locally damaging winds and hail as the main
concerns. It should be noted that there is a lot of model
disagreement during this period so will continue to monitor closely
as new data becomes available. But for now, will continue with
chance PoPs overnight.

Broad upper level ridging will build in across the southern half of
the CONUS, displacing most of the upper level energy north of our
area for the much of the work week. But, our position on the west
side of the Atlantic High will place us under deep SW flow resulting
in hot and muggy conditions. Afternoon max temps Tuesday through
Thursday will reach into the 90s, likely surpassing convective temps
and resulting in diurnal chances of showers and storms. Atmospheric
environment will be similar to this past week with high CAPE/low
shear with chances of pulse storms with locally heavy rainfall
possible. We`ll also have to monitor heat indices for areas west of
I-65 during this stretch as dew points surge into the 70s, resulting
in apparent temperatures in the low 100s.

By Friday, a cold front is progged to sweep through the region
followed by high pressure that could lead to a dry and cooler
weekend. But given model disagreement and late period uncertainties,
will stick with model blend of chance PoPs for periods throughout
the weekend.

&&

.Aviation...(00Z TAF Issuance)
Issued at 755 PM EDT Sun Aug 8 2021

Mostly clear skies and VFR to begin this TAF period with breezy
southerly winds. Watching a line of strong thunderstorms oriented
north-south push east across Illinois and southeastern Missouri.
Environment downstream does not support maintenance of the line, so
expecting the convection to gradually weaken after 01z. Showers, and
perhaps some lingering thunder, could arrive at HNB as early as 04-
06z. Areas west of I-65 in central KY have the best shot at seeing
showers between 06-10z before the line dissipates. Additional TSRA
are likely to develop after 15-16z and could potentially impact any
of the terminals Monday afternoon and evening. Brief torrential
rainfall and locally gusty winds, along with lightning, are the
primary aviation hazards.


&&

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

$$

Update...EBW
Short Term...AMS
Long Term...CG
Aviation...EBW