Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 281733
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
133 PM EDT Tue Jul 28 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1020 AM EDT Tue Jul 28 2015

Going forecast looks good.  Just adjusted hourly temps/dewpts to
current obs.  Still looks like a hot, muggy day with isld
showers/storms possible.  High temps should range through the upper
80s/lower 90s with max heat index values between 100-103 mainly
along and west of I-65.

.SHORT TERM (Now through Wednesday)...
Issued at 320 AM EDT Tue Jul 28 2015

Ohio Valley remains under weak NW flow on the periphery of the hot
upper ridge, currently centered over the southern Plains. Low-level
air mass is quite juicy, with moisture pooling near a weak
quasi-stationary front draped across southern Indiana. However,
coverage of showers and thunderstorms has remained limited by a
respectable mid-level cap.

Expect today`s convective behavior to be fairly similar to Monday,
with isolated storms popping any time after noon. Instability is
decent but not impressive, and shear is almost nonexistent, but
heavy rain will be the main threat under the stronger updrafts.
While storms today will be diurnally driven, coverage will be
greater on Wednesday as a disturbance moving into the Great Lakes
flattens out the upper ridge, and a stronger surface front heads
toward the Ohio Valley. With enough destabilization, a few of the
stronger storms could produce marginally severe winds, especially
later in the day.

Very warm and muggy conditions will continue through Wednesday, as
the surface front will not wave far enough in any direction to
change the air mass at all. Temps in the lower 90s and dewpoints in
the lower/mid 70s both day will yield afternoon heat indices just
above 100 along and west of I-65, so will cover that in a SPS.

.LONG TERM (Wednesday Night through Monday)...
Issued at 245 AM EDT Tue Jul 28 2015

The synoptic pattern at the start of the long term period will
feature a ridge across the south-central CONUS, with a trough
building into the north-central CONUS.  This trough will build into
the Ohio Valley through the period, shunting the oppressive
heat/moisture to the south making for a generally dry long term
forecast.

The long term period will start out with a cold front right on the
doorstep of the LMK CWA.  Mass convergence along the front should be
enough to lift a moderate to strongly unstable environment,
characterized by MLCAPE values of 2000-3000 J/kg, resulting in
scattered thunderstorms.  Troposheric flow is rather meager with
0-6km shear on the order of 10-20 knots, so storms will be have
trouble organizing.  That being said, precipitation loading coupled
with relatively steep low-level lapse rates will support an isolated
damaging wind threat in the stronger downdrafts.  Given this threat,
agree with SPC`s Marginal outlook for Wednesday evening into early
Wednesday night.

The front and associated precipitation will push east of the region
Thursday morning, allowing cooler and drier air to filter into the
Ohio Valley through at least Friday night.  Highs Thu/Fri will be in
the mid 80s with dewpoints in the lower 60s.

On Saturday, a rather weak and moisture-starved front will attempt
to push towards the Ohio River.  While an isolated shower/storm is
possible with this feature, chances appear to low to warrant any
mention at this time.  This front will wash out before it makes full
progress through the Ohio Valley, so temperatures should begin to
warm Sunday into Monday as readings creep back into the upper
80s and lower 90s.

&&

.AVIATION (18Z TAF Update)...
Updated 125 PM EDT Tue Jul 28 2015

Isld to scattered t-storms will continue to develop over the region
this afternoon/evening as upper level shortwaves on the NE side of
an upper ridge continue to spark convection in a moist, unstable
atmosphere.  Because coverage of storms is not great and confidence
is low if one will hit a TAF site, left VCTS in the TAFs through
this evening.  Will need to add a tempo if a cell develops near the
TAF sites though.  We should see a break in activity tonight with
winds going calm or light and vrb.  Some light br or hz is expected
at all TAF sites.  Winds will be WNW mainly staying under 7kts for
tomorrow with an approaching cold front bringing another chance for
shower/storms.

&&

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

$$

Update.........AMS
Short Term.....RAS
Long Term......KJD
Aviation.......AMS





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