Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 170527

Area Forecast Discussion
National Weather Service Louisville KY
127 AM EDT Thu Aug 17 2017

.Forecast Update...
Issued at 830 PM EDT Wed Aug 162017

In general seeing the diurnal storm activity waning...but do have
some thin lines of convergence focusing storms just west of Tell
City, IN and south of Russellville, KY. Have backed off rain chances
across the region the rest of the night, but cannot rule out these
bands holding together through the night, affecting narrow
corridors. It will be a muggy night, with lows again generally in
the 70s.


.Short Term...(This evening through Thursday night)
Issued at 253 PM EDT Wed Aug 16 2017

Scattered storms have developed along a boundary across portions of
south central KY this afternoon with a few showers and storms to the
north of this boundary. South of the boundary dewpoints are in the
mid to upper 70s with lower 70s to the north of it. These storms are
expected to continue to lift to the north through the late afternoon
hours. They should decrease in coverage through the early evening as
we lose the heating of the day. Through the overnight hours the best
chance for any storms/precipitation looks to be across southern IN
as a weak disturbance crosses the area.

For Thursday, a cold front will approach and move through the area.
Dewpoints will rise into the mid 70s ahead of this front.
Precipitable water values will rise to near or a bit above 2".
Showers and storms will likely be ongoing along the front north and
west of the forecast area on Thursday morning. Additional storms are
expected to develop across southern IN and central KY by mid day to
early afternoon. With high PWAT values and moderate CAPE of 1500-
2000 J/kg a few stronger storms will be possible in the afternoon.
However, shear values will be on the lower side. The strongest
storms tomorrow could produce small hail and isolated damaging wind
gusts along with very heavy downpours. The timing for the strongest
storms would be from mid afternoon through the early evening. These
storms will move out through the overnight hours Thursday night as
the cold front moves through.

Low temperatures will remain on the warmer side tonight, dropping
only into the lower to mid 70s. Highs tomorrow will top out in the
mid to upper 80s. Lows tomorrow night will be cooler than tonight
across mainly southern IN as the somewhat drier air filters in
behind the front.

.Long Term...(Friday through Wednesday)
Issued at 309 PM EDT Wed Aug 16 2017

Friday Through the Weekend...

Troughing will develop aloft across the eastern CONUS on Friday in
the wake of the front. A shortwave moving through this flow looks to
provide the focus for isolated to scattered storms mainly on
Saturday afternoon. Otherwise, this time frame looks mostly dry.
Temperatures will be just a bit cooler on Friday and Saturday,
topping out in mainly the mid 80s. We should then see a bit of a
warm up by Sunday back into the upper 80s to around 90.

Eclipse Day...

The thinking for Eclipse day remains largely the same as from the
previous forecast this morning. Upper level ridging will build into
the area. However, with the heat of the day some instability will
develop. The latest operational runs of the GFS, ECMWF and Canadian
all continue to depict some showers or storms developing mid/day
early afternoon across central KY and southern IN. The GFS ensemble
members for BWG are split with only a few members producing QPF.
Given we will be under the ridging and there is a lack of a trigger,
coverage of showers and storms at this time is expected to be
isolated in nature. Following along, cloud cover looks to be in the
30-40% range during eclipse time.

The other concern for the day will be the heat. Despite temperatures
likely dropping a few degrees for the hour or so on either side of
the maximum eclipse, highs look to top out in the upper 80s to
around 90. Maximum heat index values will be in the mid to upper
90s. Those outside to watch the eclipse through this time frame
should plan accordingly and have plenty of water available.

Tuesday Through Tuesday Night...

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


.Aviation...(06Z TAF Issuance)
Issued at 125 AM EDT Thu Aug 17 2017

Isolated showers will track across central Kentucky in the near term
associated with weak moisture transport. This activity should push
north/northeast of SDF and LEX by sunrise, at which there could be
some light fog developing across all of central Kentucky.

Ahead of an approaching cold front, south to southwest winds will
become gusty 20-22 kts at all of the TAF sites late this morning and
this afternoon. During peak heating, scattered showers and
thunderstorms are forecast with the peak timing window 18-23z. Rain
chances will diminish west to east toward sunset.




Short Term...EER
Long Term...EER
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