Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 180555
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
155 AM EDT THU AUG 18 2016

...Updated Aviation Discussion...

...Forecast Update...
Issued at 930 PM EDT Wed Aug 17 2016

Went ahead an put some patchy fog into the forecast over southern
Indiana and north central Kentucky for late tonight into early
Thursday morning. Dew point depressions are already tightening and
should become quite narrow later tonight. Upstream early this
morning dense fog formed over southern Illinois despite the fact
that skies were nearly overcast with mid/high clouds. Also, recent
satellite loops have been showing breaks developing in the mid/high
clouds over the lower Ohio Valley this evening. While low stratus
development may help to keep fog from becoming widespread dense,
felt the chance of fog was enough that it should be included in the
forecast. This also puts LMK in good agreement with surrounding NWS
offices that have included fog in their grids as well.

.SHORT TERM (Now through Thursday Night)...
Issued at 255 PM EDT Wed Aug 17 2016

Tonight...

Well the low clouds and rainy mid August day resembles more of a
early November day...except that its around 80 F. The surface
boundary is slowly moving SE and consequently storms too.  Most of
the storms are going to be south of the Bluegrass Parkway with bottom 3
tiers of counties the highest early evening POPS. Overall, the main
threat continues to be localized heavy rainfall and localized
flooding concerns.  The upper wave over the Land of Lincoln will
depart off to the east and reduce most of the POPS by 03z.  The HRRR
has been doing a great job on this. Some concern with fog/stratus
potential overnight given that we`ll start with narrow temp/dewpoint
spreads, but expect just enough mid-level cloudiness and boundary-
layer wind to lift the trapped moisture into a stratus deck.

Thu-Thu Night...

The front may try to wave north a tad after stalling out near I-40.
With the front in close proximity, still can`t rule out an isolated
shower or storm north of the Parkways during the afternoon/eve, but
main threat of precipitation would be further south...perhaps south
of the Cumberland Parkway where we will keep chance PoPs going.
Convection will be diurnally driven and should fade quickly after
sunset, leaving behind potential overnight fog/stratus again.

.LONG TERM (Friday through Wednesday)...
Issued at 305 PM EDT Wed Aug 17 2016

...Round of Strong Storms Possible Late Saturday and Early Sunday...
...Drier and Much Cooler Conditions Expected Next Week...

Fri-Fri Night...

More of the same summertime pattern is expected with weak upper flow
and a moist and unstable boundary layer. Diurnal pop-up storms on
Friday with the best chance across south-central Kentucky where low-
level moisture is most plentiful.

Sat-Sun...

Upper-level trof will dig into the Plains on Saturday and drive a
surface cold front SE into the Ohio Valley. Precip chances will ramp
up fairly sharply with likely POPs west of I-65, and high-end chance
POPs even getting into the Bluegrass region by late in the day.
Dynamics with this system will support strong storms, but with the
main convection coming through Saturday night during a minimum in
instability, that will temper our severe chances. Sunday will be
largely a transition day, with muggy conditions holding on. Precip
chances will linger at least into the morning, especially across the
Bluegrass and in south-central KY.

Sun Night-Wed...

Broad upper trof takes control east of the Mississippi, with a
Canadian high settling into the Great Lakes and eventually the Ohio
Valley. Monday and Tuesday will be a taste of early fall weather,
with temps a good 10 degrees below normal, and dewpoints in the
upper 50s to around 60. Temp forecast is slightly under the extended
GFS and Euro MOS, both of which may very well be biased toward
climo.  By Wednesday temps and dewpoints will begin to recover
toward more typical late August levels under shortwave ridging
aloft.

&&

.AVIATION (06Z TAF Update)...
Issued at 145 AM EDT Thu Aug 18 2016

Currently, weak surface high pressure resides over the lower OH and
TN Valleys. Despite this, a stream of moisture and some showers is
streaming ENE from parts of middle TN across south-central KY, and
these could well affect BWG thru 10z or so. To the north, conditions
currently are VFR at SDF but LIFR at LEX due to cigs at 200 ft.

Model soundings and cross-sections suggest ample boundary layer
moisture will lead to a continuation or development of low clouds
overnight, with SDF deteriorating to IFR cigs and MVFR or perhaps
brief IFR vsbys overnight into mid morning Thursday. Conditions
should continue as IFR or LIFR due to low clouds at LEX, which
should keep vsbys around 2 or 3 SM. Meanwhile, lower cigs and vsbys
also may develop at BWG toward daybreak, but be mainly MVFR.

Bkn-to-ovc low clouds may linger much of the day, especially at SDF
and LEX, but should rise to VFR levels by afternoon along with VFR
vsbys by late morning or early afternoon. BWG also should become
VFR. Winds will be southwest at 5-10 kts Thursday. For Thursday
night, boundary layer moisture may again mean lowering cigs and
vsbys toward the end of the forecast period.

&&

.LMK Watches/Warnings/Advisories...
KY...NONE.
IN...NONE.
&&

$$

Update.........13
Short Term.....JDG/RAS
Long Term......RAS
Aviation.......TWF



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