Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 170943

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

...Updated Aviation Discussion...

.Short Term (Now through Friday)...
Issued at 245 AM EDT Thu Aug 17 2017

Early this morning low pressure over Minnesota had a cold front
dropping south to Oklahoma. By this evening the low will advance to
near the Keweenaw Peninsula with its trailing cold front approaching
the Wabash Valley. Showers and thunderstorms will be found along and
ahead of the front, and will move through southern Indiana and
central Kentucky this afternoon and evening as the front comes into
the region and interacts with 2" precipitable water air. The best
upper support will be to our north closer to the 5H low and surface
cyclone over the U.P., plus upper jet energy from the Midwest to the
Great Lakes. Nevertheless, we`ll become unstable this afternoon with
LI around -5 and CAPE 1500-2000. The best 0-6km bulk shear, around
30-35kt, will be found along and north of I-64. Freezing levels will
be high so severe hail is unlikely, but progged moderate DCAPEs and
precipitation loading will pose the threat of gusty winds,
especially over southern Indiana and north central Kentucky where
there should be the best storm organization. We saw some gusts of 30-
40mph in storms yesterday afternoon with less favorable conditions.

High pressure will build in for Friday with dry weather and lower
dew points. Some valley fog may be possible around dawn if the
clouds from the overnight cold front can clear out quickly enough.

.Long Term (Friday Night through Wednesday)...
Issued at 302 AM EDT Thu Aug 17 2017

Friday Night Through the Weekend...

After an uneventful Friday night with weak surface high pressure in
place, an upper trof will pass overhead on Saturday. There won`t be
much moisture to work with but a few showers and thunderstorms could
develop, especially over southern Indiana and north central
Kentucky. Ridging will then build in at the surface and aloft with
dry conditions Saturday night through Sunday night.

Eclipse Day...

Still no significant changes in the outlook for Monday. Ridging will
continue at the surface and aloft, discouraging shower/thunderstorm
development. GFS has flip-flopped back to a dry solution while the
ECMWF still generates QPF. Most GEFS members show flat QPF plume
lines and plan view QPF analysis shows more than half of the
individual members are dry, with the wet solutions showing only
light, scattered precipitation. About half of the members of the EPS
are dry as well, and EPS is favoring partly cloudy skies (as opposed
to mostly cloudy or cloudy). Still can`t rule out isolated pop-ups
in the warm, humid afternoon so will hang onto very small PoPs, in
the teens to around 20%. The best chances should be west of
Interstate 65 where the better moisture supply will reside.

Speaking of warmth and humidity, of possibly greater significance
will be heat index readings. As air temperatures crest around 90
with dew points around 70, heat index readings will peak in the
middle 90s, especially west of I-65. Locally higher values may be
attainable in some spots such as over green fields where
evapotranspiration will be maximized. Three to five hours of heat
index readings near or above 95 will be possible in the afternoon
west of I-65.


Another upper trof will move in for Tuesday. A surface cold front
will come in from the northwest and may lay out in an east-west
alignment, keeping shower and thunderstorm chances in the forecast
for both days.


.Aviation...(06Z TAF Issuance)
Issued at 540 AM EDT Thu Aug 17 2017

An approaching cold front will bring scattered showers and
thunderstorms to the TAF sites later today. The latest guidance
suggests showers will push into central Kentucky between 18 and 20z
then continue through 00-02z at LEX. Overall ceilings should remain
VFR outside of any thunderstorms. Winds will become gusty 20-22 kts
this afternoon. In the wake of the frontal passage late tonight,
mostly clear skies are expected with westerly winds.




Short Term........13
Long Term.........13
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