000
FXUS63 KLMK 212320
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
720 PM EDT Fri Jul 21 2017

...Updated Aviation Discussion...

.Short Term...(This evening through Saturday night)
Issued at 252 PM EDT Fri Jul 21 2017

...Oppressive Heat and Humidity Through Saturday...

Summer heat and humidity is in full force this afternoon across the
lower Ohio Valley with the latest observations showing readings in
the lower to middle 90s. While not unusual for July in the lower
Ohio Valley, the dewpoints in the middle to even upper 70s are the
real driver for how oppressive it feels outside. Latest heat indices
are in the 100s with some of the highest readings near 110.

The main weather message through this weekend will be the heat and
high humidity but complicating the forecast is thunderstorm chances
for portions of the area.

For this evening, earlier outflow boundary draped across central
Kentucky has really washed out and thanks to very warm mid level
temperatures and the upper ridge, the atmosphere isn`t supporting
much in the way of vertical growth. Further to the north across
Indiana and Ohio, the mid level capping inversion is weaker which
has allowed some convection to pass through. The bulk of the local
area will likely stay dry this evening and tonight, though can`t
rule out an isolated pop-up shower across portions of southeast
Indiana and the northern Bluegrass.

Lows tonight will stay well into the 70s and likely not drop below
80 or 81 in the Louisville metro. The warm minimum record is 81 from
1934 for reference.

As for Saturday, a near repeat of today with a morning MCS likely to
be tracking across central Indiana and central Ohio. Outflow and
convective debris clouds will likely be spilling over the area
during the morning hours. The upper ridge is just slightly weaker so
the better chances for diurnally driven convection will be found
across portions of southeast Indiana and north central Kentucky. If
a stronger storm were to develop, strong winds and heavy rainfall
are the main threats. Temperatures will again climb into the lower
to middle 90s. Peak afternoon heat indices will top out in the 105
to 110 range in the advisory area with other locations in the 100 to
104 range.

.Long Term...(Sunday through Friday)
Issued at 300 PM EDT Fri Jul 21 2017

Sunday into portions of early next week the upper ridge breaks and
eventually a surface front will pass through the area. This will
bring greater coverage and chances of showers and storms though it
doesn`t appear that it`ll be widespread beneficial rainfall for
everyone.

On Sunday, southern Indiana and northern Kentucky will see some
reprieve from the high heat and humidity, however south central
Kentucky will likely stay ahead of the front and under the influence
of the upper ridge. Afternoon heat indices across that area will top
out in the 100 to 104, and an extension of the heat advisory may be
necessary for some areas.

High pressure noses down into the lower Ohio Valley on Monday though
the surface front is forecast to stall out around the KY/TN border.
This will keep slight chances of showers/storms in the forecast for
those border counties while the northern areas and southern Indiana
get slightly drier air and more normal temperatures.

Moisture returns to the area mid-week with pop-up showers and storms
possible across the area. Temperatures will trend toward climatology
- upper 80s to low 90s and lows in the upper 60s to lower 70s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 720 PM EDT Fri Jul 21 2017

Main issue at this time is haze, but current visibilities all are in
the VFR range. May see them drop down to MVFR by daybreak at
SDF/LEX. Next issue would be storm chances. Cannot rule out an
isolated storm just north of the SDF/LEX corridor this evening and
then again tomorrow afternoon...but chances are too low to include
in this set of TAFs.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ076>079-
     083-084-089>092.

KY...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for KYZ023>034-
     038-045-053-061>063-070>074.

&&

$$

Short Term...ZT
Long Term...ZT
Aviation...RJS