Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 180722
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
322 AM EDT Tue Apr 18 2017

.Short Term (Now through Wednesday)...
Issued at 315 AM EDT Tue Apr 18 2017

Current wx pattern is marked by zonal flow aloft, with E-NE low-
level flow around a strong sfc high over eastern Canada funneling
dry but mild air into the Ohio Valley. The front that moved through
early Monday is still evident in a fairly sharp dewpoint gradient
over southern Kentucky, and this boundary is expected to be the
focus for most of our weather the next 36 hrs.

The front will continue to weaken today, but will lift slowly
northward, bringing SE flow and spreading higher dewpoints into more
of central Kentucky. Not expecting much action in the morning, but
we`ll see scattered showers and thunderstorms develop in the heat of
the afternoon. Best chances for precip will be east of I-65 and
south of the Bluegrass Parkway, with only a slight chance at best
over southern Indiana. The air mass remains quite warm, so even with
plenty of cloud cover, temps will again run solidly above climo.

By Wednesday we`ll be in broad SW low-level flow, which in itself
will keep the pattern a bit unsettled. However modest H5 height
rises will mean slightly lower precip chances, especially along and
west of I-65.

.Long Term (Wednesday Night through Monday)...
Issued at 310 AM EDT Tue Apr 18 2017

...Active Weather Expected Thursday and Saturday...

Two primary and different types of weather systems will affect the
lower OH Valley during the extended period, both which could have
significant impact.

First up is a progressive northern stream shortwave moving east
across the Great Lakes, and dragging a cold front into the Ohio
Valley late Thursday. The warm sector will be moderately unstable
with CAPE pushing 2000 J/kg in the heat of the afternoon, but shear
is fairly weak for this time of year. Can`t rule out a few strong
storms if the front arrives in time to tap the instability, with
strong wind gusts and heavy rain as the main threats. Storm
intensity will diminish as the evening progresses due to loss of
heating.

Still plenty of variation in model solutions for Saturday and Sat
night, but what remains consistent is a closed upper low developing
over the central Plains Friday night and pushing east into the Lower
Ohio Valley by Saturday night per the GFS and ECMWF, or Sunday if we
believe the GEM. General idea is to track a sfc low somewhere across
Kentucky or Tennessee Saturday afternoon or night, with fairly
copious QPF where the deep SW mid-level flow develops ahead of the
upper low, and overruns the warm front. Best rain chances at this
point appear to be Saturday afternoon and evening as a moderate
soaking rain with embedded thunder, but the timing is still up for
adjustment. Southward trend in the track of the surface low could
open a wide range in temps across the warm front, with highs
struggling into the lower/mid 60s north of the front while south
central Kentucky climbs into the 70s.

Precip chances will linger Sunday into Sunday night as the upper low
makes its way slowly ESE across the Tennessee Valley, with a drying
trend Monday as it pushes into the Carolinas and we lose the cold
pool influence. Temps will run near climo by day and a few degrees
above by night.

&&

.Aviation (06Z TAF Update)...
Issued at 155 AM EDT Tue Apr 18 2017

A band of very light showers was oriented east-west across south-
central Kentucky early this morning, along a low-level moisture
gradient. A light shower is possible at BWG through the rest of the
overnight period. Richer low-level moisture associated with a warm
front will make a northward push on Tuesday. BWG should lower to
MVFR around dawn. A brief drop to fuel alternate levels isn`t out of
the question after 12z. SDF and LEX will remain VFR throughout the
morning hours, with ENE winds becoming more easterly.

A weak shortwave trough is forecast to move over the lifting warm
front during the day, and richer moisture/daytime heating is
expected to result in modest convection. Expected scattered
showers/storms to develop after 17z. All three TAF sites could see a
brief heavier shower or storm along with brief vsby reductions.
Expect lower ceilings to linger at SDF/LEX this evening after any
showers have exited to the northeast.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

Short Term........RAS
Long Term.........RAS
Aviation..........EBW



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