Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 161712
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
112 PM EDT Wed Aug 16 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 1210 PM EDT Wed Aug 162017

Scattered showers continue to develop mainly across east central KY
early this afternoon closer to the remnants of an MCV. With the heat
of the afternoon and instability increasing, more showers and storms
are expected to form this afternoon, though coverage should remain
scattered. Cloud cover was decreased in the forecast for the next
few hours, but it should increase again this afternoon as more cu
develops.

&&

.Short Term (Now through Thursday)...
Issued at 257 AM EDT Wed Aug 16 2017

MCV traveling along the KY/TN border will produce a few showers
early this morning, however we`ll see greater shower and
thunderstorm coverage this afternoon as the atmosphere destabilizes
and surface temperature readings approach convective temperatures in
the middle and upper 80s. Mid level lapse rates will be weak, deep
layer shear and DCAPE weak, freezing levels very high, and there
won`t be much in the way of a synoptic scale trigger other than a
weak warm front that will be just off to our north by afternoon.
Nevertheless, there won`t be much capping and the atmosphere will
still become diurnally unstable with precipitable water values
around two inches. So, scattered showers and storms can be expected,
especially this afternoon and evening. Scattered showers may
continue into the overnight hours, especially in southern Indiana
and north central Kentucky closer to low- and mid-level jet energy.

It will be quite warm and muggy today with heat index readings well
into the middle 90s this afternoon west of Interstate 65.

On Thursday a cold front will approach from the west, reaching the
Wabash Valley by evening. The atmosphere will be slightly more
unstable tomorrow with better shear and slightly deeper moisture.
Though lapse rates and DCAPE will still be weak, and freezing levels
will still be very high, the incoming cold front along with a 5H
speed max will provide enough support for some stronger storms by
afternoon. The best chance for strong storms should be along and
north of the Ohio River closer to the cold front and upper support,
along with weaker capping. The main threat will be gusty winds with
the most intense downpours.

Though temperatures Thursday afternoon will be similar to what we
see today, heat index readings may peak just a bit higher thanks to
moisture pooling ahead of the cold front. As dew points climb into
the middle 70s the heat index will approach 100 along and west of
Interstate 65 and the middle 90s to the east.

.Long Term (Thursday night through Tuesday)...
Issued at 319 AM EDT Wed Aug 16 2017

Thursday Night Through the Weekend...

The cold front discussed in the short term will cross the region
Thursday night, accompanied by showers and thunderstorms. Model data
suggest a line of storms, potentially strong, will accompany the
front. Friday through Sunday look relatively quiet with weak ridging
at the surface, but an upper shortwave trough will pass overhead on
Saturday and could spark a few thunderstorms.

Eclipse Day...

Bottom Line: Overall still looks like a decent day, but there are a
couple of concerns.

Upper ridging will attempt to build in over the southeast United
States Sunday and Monday. This pattern is usually favorable for
generally suppressing convection.

GEFS QPF plumes are quite flat on Monday, with just a few of the
individual members indicating precipitation. Looking at plan views
of all ensemble members on the latest available run, only four have
QPF in central Kentucky and the amounts are very low. GEFS is
showing less than 0.05" of precip Monday over the region as a whole.
Going through the last seven runs of the operational GFS, the
relative wetness of the current run is a departure from the drier
previous six runs that showed just a few isolated patches of QPF, if
any. MEX PoPS are right around CLIMO.

On the ECMWF ensemble, about half of the members indicate QPF
Monday, mostly light. EPS is showing only around 40% cloud cover at
18Z Monday. ECE PoPs are below CLIMO.

Difficult to find much of a trigger outside of daytime heating
thanks to the aforementioned upper ridge along with surface high
pressure over the Atlantic extending westward into the eastern
United States.

Still, soundings show little capping and enough instability to
support convection. So, given all of the above, the scenario, as it
appears right now, looks like a typical hot and humid summer day
with spotty afternoon showers/storms developing in the heat of the
day.

Speaking of hot and humid...from a public safety standpoint the
greater issue on Monday may be the heat. Afternoon temperatures will
peak around 90 (notwithstanding a drop of a few degrees in areas of
greatest eclipse influence) with dew points around 70. That will
result in heat index readings in the middle 90s, possibly upper 90s
west of I-65 and south of the Ohio River.

Tuesday...

An upper trough will swing through the Great lakes Tuesday and will
bring an increased chance of showers and thunderstorms to the Ohio
and Tennessee Valleys.

&&

.Aviation...(18Z TAF Issuance)
Issued at 111 PM EDT Wed Aug 16 2017

Partly to mostly sunny skies were noted across the region this
afternoon.  One area of convection is moving northeastward through
the Bluegrass region and another is moving in from the Land Between
the Lakes region.  These showers will affect KBWG and KLEX early in
the TAF period.  Additional scattered showers and storms are
expected this afternoon, therefore we will continue to carry VCTS at
the terminals through the evening hours.  Mainly VFR conditions are
expected overnight with some patchy fog being possible at KBWG and
KLEX.  Winds this afternoon will remain out of the southwest at 5-
10 kts with light and variable winds expected overnight.

&&

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

$$

Update............EER
Short Term........13
Long Term.........13
Aviation..........MJ


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