Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/25/19

Area Forecast Discussion

National Weather Service Louisville KY

 720 PM EDT Wed Apr 24 2019

...Updated Aviation Discussion...

.Forecast Update...
Issued 709 pm EDT Wed Apr 24 2019

Instability is waning as the sun sets. The storms to our west are
spreading out into a large area of light to moderate rain, with a
few weak thunderstorms on the leading edge, beneath the entrance
region of a small upper jet max. This area of convection will
continue to slide up the Ohio Valley this evneing, bringing a
soaking rain to southern Indiana and extreme north central Kentucky.

Issued at 530 PM EDT Wed Apr 24 2019

Compared to yesterday evening, shear is stronger today however
instability is weaker, with the latest SBCAPE analysis showing
values of 500-1000 J/kg south of a warm front draped across southern
Indiana. DCAPE is much weaker as well. Cumulus popped earlier today
as convective temperatures were reached, but have begun to struggle
a bit as cirrus increases overhead, flowing off storms to our west.

AMDAR soundings do show some capping around 8000 feet, but showers
and storms are still likely to move in during the mid-late evening
hours. So far the storms upstream have been producing mostly pea
sized hail with only isolated instances of anything larger (similar
to what we saw here yesterday evening). Mesoscale models show this
will continue to be the case as the storms moves east. The most
likely geographic area for any stronger storms appears to be 1-2
counties either side of the Ohio River, especially from Louisville
west. By the storms reach east of Louisville instability should wane
enough to cause the risk of strong/severe storms with hail or
damaging winds to diminish.

&&

.Short Term...(This evening through Thursday)
Issued at 305 PM EDT Wed Apr 24 2019

...Waves of Showers and Storms Through Thursday...

Warm front has lifted north into southern Indiana, with an
approaching upper wave already triggering convection over southeast
Missouri and southern Illinois. Expect the boundary to guide these
storms ENE, generally very close to the Ohio River. Should get into
the Hoosier National Forest by 21-22Z, then push eastward into
Louisville around sunset and on toward Lexington and Frankfort as
the evening progresses.

SPC just shows a general thunderstorm risk for the area in the Day 1
Outlook, but with temps into the mid/upper 70s into the I-64
corridor, we should have at least marginal instability to tap into,
and that will make roughly 40 kt of deep-layer shear available where
we can sustain a southerly surface wind. Lighter W-SW winds will cut
into that, but can`t rule out a few marginally severe wind gusts.
Perhaps the bigger threat would be flooding, given a fairly small
angle between the orientation of the front and the storm motion, but
that will take a while to develop if the action stays just north of
the river this evening. Marginal Risk for excessive rainfall per WPC
is in line and we will include localized flooding in our messaging.
Precip chances will taper down rapidly south of the Western Kentucky
and Bluegrass Parkways, with much of south central Kentucky staying
dry.

Expect a break in the action around midnight, but another impulse
will eject out of the deep trof over Oklahoma and Texas, bringing
another wave of showers Thursday morning. Not much instability
available for strong storms, so this will be primarily showers with
perhaps a stray rumble of embedded thunder.

Could see yet another wave later in the day as the upper trof works
its way east to the Mississippi River and southerly flow deepens
ahead of it. Not enough confidence in any storm severity, but
depending on where the heaviest rain falls with each wave the
flooding risk may continue to increase.

.Long Term...(Thursday night through Wednesday)
Issued at 320 PM EDT Wed Apr 24 2019

Headed into Thursday night, a closed off upper low traveling up the
Mississippi Valley opens and becomes part of the mid-level trough
traveling up the Ohio River Valley. A shortwave embedded with this
trough and low pressure at the surface help to force an
intensification of precipitation. Mostly a rain event with a chance
of some isolated thunderstorms. The better chance of thunder will be
further south near the Tennessee / Kentucky border.

Friday morning, a shortwave just behind the center axis of the mid-
level trough acts as a squeegee wiping most of the rain out of
southern Indiana and central Kentucky. By afternoon, skies should be
clear and high temperatures will be limited by gusty cool air
advection from the northwest. Wind gusts are expected around 25 mph.

On Saturday, surface high pressure and ridging try to take hold over
the CWA, and they do for awhile. With the center of the high passing
just south of Kentucky, winds will shift from the northwest to
south. This doesn`t affect temperatures a whole lot, but it does
start feeding moisture from the Gulf to a large surface low centered
in northern Iowa at the time. That low system won`t have a lot of
moisture to work with, but it will have enough that the weak cold
front trailing the surface low will give areas near the Ohio River a
20 percent chance of PoPs.

Mid-level flow becomes very flat from west to east. Sunday appears
to be a partly sunny as high pressure passes behind the cold front
from Saturday.

From Monday through Wednesday, a stationary front wants to set up
near the area, kind of like current condition. This front would run
west to east. Areas north of the front would see waves of passing
showers while areas to the south would remain much drier. From that
point on, things look like they they could stay wet for awhile, but
that`s a week away. Things can change.

&&

.Aviation...(00Z TAF Issuance)
Updated at 720 PM EDT Wed Apr 24 2019

Moisture will continue to flow northward ahead of an approaching
upper trough approaching the Mississippi Valley tonight. Also,
surface low pressure will develop over the Ozarks tomorrow morning
and head northeast into the Ohio Valley, keeping showers and a few
thunderstorms in the forecast. The best chance for the most
widespread shower activity, and any thunderstorms, should be
Thursday afternoon and evening as the low approaches. Winds,
ceilings, and visibilities will be variable as showers move in and
out and the surface low nears, especially at HNB/SDF/LEX.

&&

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

$$

Update...13
Short Term...RAS
Long Term...KDW
Aviation...13