Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 171728

Area Forecast Discussion
National Weather Service Louisville KY
128 PM EDT Thu Aug 17 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 1102 AM EDT Wed Aug 17 2017

Issued a small forecast update a little while ago to bring up cloud
cover in the SE along with increasing PoPs as a band of scattered
showers moved northeast just north of the Lake Cumberland region. In
other areas, we lowered cloud cover forecasts a bit, given the
mostly sunny conditions.  Clouds were increasing from the west
however.  Current temperatures are in the low-mid 80s across the

Current forecast remains on track for this afternoon.  Surface cold
front out to the northwest will move southeastward toward the region
this afternoon.  Initial line of showers and storms will continue to
develop across central IN and move northeastward into W/C Ohio later
this morning into the early afternoon hours.  Much of southern IN
and Central KY will continue to destabilize through the early
afternoon hours.  Convective temperatures should be reached in the
17-18Z timeframe with convection developing in a likely SW-NE line
from western KY into southern Ohio.  Afternoon CAPE values still
look to surge over 1500 J/KG along with 30-35kts of bulk shear.
However, atmosphere will be pretty loaded with moisture and the
models still suggest DCAPE values increasing through the afternoon.
Bottom line is that strong storms will be possible across the region
this afternoon with torrential rainfall, gusty winds, and frequent
lightning being the main threats.  Still think that best overall
threat of severe weather will remain just to our north from central
IN into Ohio where higher bulk shear values and stronger influence
of upper jet streak reside.


.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...(18Z TAF Issuance)
Issued at 126 PM EDT Thu Aug 17 2017

Showers and thunderstorms have begun to develop ahead of an
approaching cold front. These storms may affect the TAF sites this
afternoon into the evening hours. These storms will produce heavy
rainfall that will reduce visibilities if they directly affect the
airfield, so have included TEMPO groups at each site during the most
likely window for storms. These storms should move east of the
region by 00-02Z. However, a few showers may linger around LEX
through 06Z or so.

Winds whit afternoon will be gusty out of the southwest. The gusts
should subside this evening and winds will shift to more westerly
behind the front overnight. Some low stratus looks to develop at LEX
tonight with MVFR to possibly IFR cigs developing. BWG is more
questionable with the ceilings as clouds may start to break up there
earlier with the front passing through, so have kept clouds
scattered early tomorrow morning.




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