Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 161038
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
638 AM EDT Wed Aug 16 2017

...Updated Aviation Discussion...

.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...(12Z TAF Issuance)
Issued at 625 AM EDT Wed Aug 16 2017

Patchy fog continues across central Kentucky and portions of
southern Indiana this morning. As high clouds move in from the west,
this should help limit fog expansion but couldn`t rule out some
drops at BWG and LEX through 8 am EDT or so. Otherwise, a weak mid
level wave will brush over the region and combined with daytime
heat, should help narrate showers ans thunderstorms. The greatest
chances will come this afternoon at SDF and LEX.  By late afternoon
to early evening, showers/storms will begin to dissipate with loss
of peak heating. Another round of light fog is possible again
tonight at the TAF sites.

&&

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

$$

Short Term........13
Long Term.........13
Aviation...ZT



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