Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 200719

Area Forecast Discussion
National Weather Service Louisville KY
319 AM EDT Sun Aug 20 2017

.Short Term (Now through Saturday)...
Issued at 255 AM EDT Sun Aug 20 2017

...Lazy Hazy Dog Days of Summer...
...MCS cloud shield approaches ahead of the eclipse...

Well...for the Sirius dog days of summer typical dew points in the
upper 60s to low 70s. The Ohio Valley is under weak sfc high
pressure with a quasi stationary front from CRW-ILN-STL.  One rogue
storm formed along the far southern OH/IN border.

Pre 1st period...

The overnight story really is the affect of radiation fog. The
moderate mixing on Saturday brought some crossover T Td into play
using the UPS fog technique.  The GOES 16 fog 20.3-3.9 um loop
showing patchy fog increasing especially along some of the lakes and
rivers. We will be watching this close to see if any enhanced
wording is necessitated.

Sun-Sun night...

Sct Cu will once again form today with CI/CS moving in from MCS over
Hawkeye State.  This MCS will dwindle this morning and then reignite
during the afternoon and approach Wrn IL and Nrn MO. More
importantly is the affect of the upper level cloudiness. Believe CWA
will be at least strands of and filaments (high cloud 1) approaching

Highs today look dry and mostly sunny, with highs 88 to 93. With the
stationary front just to the north, expect isolated storms to be
just a north of the CWA and high resolution models have captured
this, so increased POPS to 10% in top tier of Srn IN during

Solar Eclipse Monday...

Yes it will be a hot and humid day for the solar eclipse with highs
89 to 94 degrees, with the hardest part of the forecast the cloud
cover. The MCS will reform over IA and push its cloud shield SE in
the NW flow pattern.  Upper cross sections showing >60% RH (GFS much
more) 12-18z. Coordinated with IND/ILN/BNA/PAH on sky cover and we
are all increasing sky cover along and N of I64 and slight increase
south of I 64.  Soundings support 2/8 to 3/8 CU at 18z.  Right now
LMK will have about 45% sky cover at 18z. It is a tough forecast,
but right now the path of totality should be ok with some cloud
cover, with heat indices a definite concern in the 94-99 range.

If the convection forms further south, like the ARW model is
suggestion, a much more pronounced CI/CS shield will occur. This
would be more opaque for Srn IN and Nrn KY.  The new 12z run should
get a better handle on the cloud shield. Like mentioned already, the
595m upper ridge over Great Smoky NP TN will keep most of the clouds
to the North.

Increased POPS to 10-14% overnight Monday night, with a potent front
coming down for Tuesday evening.

.Long Term (Saturday Night through Thursday)...
Issued at 305 AM EDT Sun Aug 20 2017

Tuesday - Wednesday...

A strong cold front will approach the area Tuesday and slowly move
through Tues night into Wed. The front will likely bring a line of
strong to severe storms Tues afternoon/evening.  Soundings indicate
2000-3000 j/kg of CAPE will be achievable Tues afternoon ahead of
the convection with 0-6 km bulk shear values of 25-35 kts.  These
parameters would suggest storm strength could reach strong to severe
levels with strong winds being the main threat Tues
afternoon/evening.  Weaker precip along the front may linger into
Wed morning.

As for temps, Tuesday looks to be the last hot and muggy day.  Highs
will range from the mid 80s to low 90s across the region with heat
indices maxing out in the mid to upper 90s before convection
arrives.  Temps will remain mild Tues night with lows ranging
through the 60s to around 70.  Relief from the heat/humidity will
come Wed with highs in the upper 70s/lower 80s.

Thursday - Saturday...

A broad trough will settle over the Midwest through Fri providing
cooler, pleasant weather.  Expect dry conditions with highs in the
upper 70s/lower 80s and lows in the 50s!  Saturday temps may begin
to warm a little more as the trough moves east of the region.


.Aviation (06Z TAF Update)...
Issued at 125 AM EDT Sun Aug 20 2017

The main TAF concern will be fog development tonight.  Think that
patchy to areas of fog will form over the region but the near sfc
environment should be dry enough to limit density.  Crossover
analysis reveals that none of the TAF sites should reach their
crossover T this morning.  However, some of the high res models are
still are hinting at some fog and even some dense fog in some areas.
Soundings support at least some fog this morning as well with light
near sfc winds and a decent inversion. Therefore, kept TAFs similar
to the previous TAF forecast with MVFR br at BWG/LEX and IFR tempo
at both.  Conditions should improve to VFR around 14-15Z with SSW
winds up to around 5-6 kts today.




Short Term........JDG
Long Term.........AMS
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