Scientific Forecaster Discussion
fxus63 klmk 201131
Area forecast discussion
National Weather Service Louisville Kentucky
731 am EDT sun Aug 20 2017
issued at 700 am EDT sun Aug 20 2017
Updated the forecast to include a small chance for rain over
southern in this morning. A small complex of storms continues to
make its way east into that region.
Short term...(today through Monday night)
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 Ohio/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.
Sct cu will once again form today with cirrus/cs moving in from mesoscale convective system over
Hawkeye state. This mesoscale convective system will dwindle this morning and then reignite
during the afternoon and approach wrn Illinois and nrn MO. More
importantly is the affect of the upper level cloudiness. Believe County Warning Area
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 County Warning Area and high resolution models have captured
this, so increased probability of precipitation 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 mesoscale convective system will reform over Iowa and push its cloud shield southeast in
the northwest flow pattern. Upper cross sections showing >60% relative humidity (gfs much
more) 12-18z. Coordinated with ind/iln/bna/pah on sky cover and we
are all increasing sky cover along and north of i64 and slight increase
south of I 64. Soundings support 2/8 to 3/8 cumulus 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 95-100 range.
If the convection forms further south, like the arw model is
suggestion, a much more pronounced cirrus/cs shield will occur. This
would be more opaque for srn in and nrn Kentucky. The new 12z run should
get a better handle on the cloud shield. Like mentioned already, the
595m upper ridge over great smoky np Tennessee will keep most of the clouds
to the north.
Increased probability of precipitation to 10-14% overnight Monday night, with a potent front
coming down for Tuesday evening.
Long term...(tuesday through saturday)
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
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...(12z taf issuance)
issued at 655 am EDT sun Aug 20 2017
The main taf concern will be fog this morning. Patchy areas of fog
have formed over the region with bwg below 1sm periodically this
morning. Will handle in a tempo group through 13z. Conditions
should improve to VFR around 14-15z with south-southwest winds up to around 5-6