Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 240012

Area Forecast Discussion
National Weather Service Louisville KY
812 PM EDT Mon Oct 23 2017

...Updated Aviation Discussion...

.Short Term...(This evening through Tuesday night) Issued at 320
PM EDT Mon Oct 23 2017

Now - Tonight...

The center of the upper low is now over the CWA, with the surface
low now over NW Indiana. Isolated to scattered light showers are
lingering with the surface low feature, however expect coverage to
increase a bit through the late afternoon and early evening as a
TROWAL evident on 700-500mb potential temperature analysis moves
into the area behind the departing upper low. Showers associated
with this feature are already ongoing across IL and western KY so
confidence better than average in scattered to numerous showers over
the next several hours. Coverage should be best across southern IN,
with lesser coverage across southern KY. It is also worth noting
that the TROWAL may lose some definition as we move deeper into the
evening so coverage of shower may diminish a bit the further east
you get.

A third round of rain is then possible overnight as the left exit
region of a 110-120 knot upper jet noses into the region. Low
confidence on how much coverage to assign this shower potential, but
there should be enough lift and lingering moisture to yield mention

Temperatures are also tricky overnight. First off, temps should fall
for the rest of the afternoon and evening as a good cold advection
component combines with cloudy skies to limit heating. Expect temps
to continue to fall through the 50s into the evening, before
settling down into the mid and upper 40s by dawn.

Tuesday - Tuesday Night...

Another vort lobe will rotate through the parent trough on Tuesday
over northern IL/IN/OH. Some pooled moisture associated with this
feature could slide across our northern CWA and possibly squeeze out
some cold advection showers. There is a bit of positive area up
above the freezing level that makes one wonder whether we could
squeeze out a couple of ice pellets with any light shower. However,
given freezing levels still 3-4 k feet and very little lift/moisture
think it`s a pretty low probability.

Trough axis swings through Tuesday night, with a dry forecast taking
over. Big question is how quickly skies clear across the western CWA
and whether any frost potential exists there. Another limiting
factor will be surface winds up a bit, so will hold off on mention
in coordination with surrounding offices.

.Long Term...(Wednesday through Monday)
Issued at 320 PM EDT Mon Oct 23 2017

Wednesday - Thursday Night...

The upper trough axis will pass east of the area by Wednesday, with
dry NW flow aloft and surface high pressure control our weather
through Thursday morning. Then, another amplifying trough will dig
over the center CONUS, transitioning our upper flow to SW ahead of
it for the Thursday/Thursday night time frame.

Under the aforementioned setup, sensible weather will feature partly
cloudy skies with highs only in the low to mid 50s on Wednesday.
There could be enough low level moisture in our far NE on Wednesday
to squeeze out a cold advection shower, but probs are too low for
any mention at this time. Otherwise, the main story will be the cool
temperatures Wednesday night, and the potential for frost. Mostly
clear skies, and dew points in the low to mid 30s would seem to set
the stage, however a bit concerned the surface and near surface
winds stay up just a bit. Will keep the current messaging for now,
but won`t play it up more than patchy frost at this point.

As heights/thicknesses rise by Thursday, look for recovering highs
in the mid 60s along with dry conditions. Thursday night lows will
be milder given the steady SSW winds that will take hold ahead of
the next approaching cold front. Look for lows in the mid to upper

Friday - Monday...

The strong upper trough will continue to amplify into the weekend,
enveloping the eastern CONUS through the weekend and into early next
week. A cold front will trail from the surface low over eastern
Canada, entering the Ohio Valley by Friday afternoon and only slowly
moving east through much of Saturday. Scattered rain showers are
expected along this feature, with another shot of cooler air lurking
behind it. Still like the idea of just keeping rain in the forecast
as cold air doesn`t look to quite catch up to lingering moisture.

We`ll return to a dry forecast for the Saturday night through Monday
time frame as dry NW flow aloft and surface high pressure build back
into the area. Temps will be below climo with highs only in the low
to mid 50s, and lows well into the 30s. More frost or even possibly
freeze potential will exist during this time.


.Aviation...(00Z TAF Issuance)
Issued at 800 PM EDT Mon Oct 23 2017

A low pressure system is centered over Cincinnati. Bands of light
showers are circling the system as they move to the east. SDF and
LEX will continue to experience temporary drops in visibilities and
ceilings as these showers pass. Another line of light showers,
currently over STL, is working towards IN and KY. Slight wind
shifts are expected. BWG is expected to remain in VFR overnight.
SDF should return to VFR shortly, and LEX is expected to remain in
MVFR until around 4z.




Short Term...BJS
Long Term...BJS
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