Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 210448

Area Forecast Discussion
National Weather Service Louisville KY
1248 AM EDT Mon May 21 2018

.Forecast Update...
Issued at 807 PM EDT Sun May 20 2018

Storms continue to pop up this evening across the region. These have
been mostly heavy rain producers with a few reports around the
region of small hail. Some stronger winds to 50 mph will be possible
as well with a cell moving eastward out of Ohio County. Storms may
continue to pop up for the next couple of hours, especially along
the multiple outflow boundaries present. As we lose instability this
evening, storms are expected to diminish in number and intensity
with most gone by late evening. Thereafter, most of the night should
be dry before additional showers move in from the west tomorrow


.Short Term...(This evening through Monday)
Issued at 345 PM EDT Sun May 20 2018

Satellite imagery shows the CWA under mostly clear skies with a line
of showers and storms west of Kentucky coming from an overnight
system that was centered in Missouri. Southern Indiana and central
Kentucky sit under an atmosphere with precipitable water levels in
the 1.3-1.5` range. Models show MLCAPE levels increase to around
1,000 to 2,000 J/kg across the CWA this evening. The surface is
relatively dry with temperatures in the upper 80s and dewpoints in
the lower 60s. The thought isn`t that much will initiate over the
CWA without interaction from an outflow boundary or two from the
storms out west. Given the conditions, scattered showers and thunder
are thought to be very likely this evening. Confidence is low as to
location and exact timing. Precipitation tonight could be heavy and
produce gusty winds.

After nightfall, Rain chances will diminish with the loss of diurnal
heating. The sky will remain mostly cloudy with lows only dropping
into the mid to upper 60s.

Near morning, a chance of showers returns. This chance is mainly for
the northern areas in the CWA. During the afternoon into evening,
surface convergence will set up over Indiana and move south firing
up convection as it moves south towards the Ohio River Valley.

.Long Term...(Monday night through Sunday)
Issued at 250 PM EDT Sun May 20 2018

Scattered showers and isolated thunderstorms will continue Monday
night, especially during the evening as deep-layered moisture
(precipitable water values around 1.5 inches) continues over the area
in the presence of marginal instability, weak forcing, and weak
shear. Any heavy rainfall producing cells in the evening should
become just isolated to scattered showers overnight. Lows will be in
the 60s for most areas.

On Tuesday, flow aloft begins to turn west-northwest which will
allow a cool front to push slowly south across the Ohio Valley. The
deeper moisture from Monday night will slowly advance eastward
accompanied by scattered showers over central KY. Behind this area,
models suggest a narrow axis of better instability and some frontal
forcing advancing southeast into southern IN and north-central/east-
central KY late in the day or Tuesday evening. Scattered thunder-
storms will be possible along this boundary, although severe storms
are not expected. Expect highs in the lower to mid 80s.

By Wednesday, the cool front will drop across our forecast area,
bringing drier weather to the area, along with slightly lower
surface dewpoints. It will still be warm during the day with highs
in the 80s Wednesday and Thursday, but nighttime lows should be a
little cooler in the upper 50s to mid 60s.

By late week and next weekend, models suggest a complex weather
pattern may try to set up across the eastern half of the U.S. A
northern stream trough is forecast to advance east/southeast across
the upper MS Valley/Great Lakes while a broad southern system of
some kind could take shape over/near the Gulf of Mexico and send
moisture northward ahead of the northern trough. As expected, models
differ quite a bit in their solutions but do show this general
signal, and model variability will likely continue over the next few
days. However, this could result in our next chance of showers over
the lower Ohio Valley sometime next weekend. The 12 UTC GEFS plumes
show precip next weekend in our area and other models tend to agree.
Before that, Friday should be mainly dry but there could be
scattered diurnal showers across parts of south-central KY. For now,
expect highs in the 80s Friday through Sunday, potentially a little
cooler Sunday if enough clouds/precip are drawn into the area.


.Aviation...(06Z TAF Issuance)
Issued at 1245 AM EDT Mon May 21 2018

Earlier precip is now dissipating over south central Kentucky, and
we should have a quiet overnight period. Renegade shower over
southern Indiana shows we can`t completely rule anything out, but it
is so localized that the chances of any TAF site being impacted by
new showers/storms overnight are too small to mention. Could see
some fog toward daybreak in BWG, given the earlier rain and jst
being a favored site for fog. Impact should be limited to MVFR.

Residual vort centers associated with Mississippi Valley convection
will offer a decent chance for showers and storms throughout the
heat of the afternoon. Confidence is too low to pin down, so will
roll wih PROB30 groups across the board from roughly 18Z onward. Any
restrictions to ceiling or vis will be quite brief, so will only
include MVFR vis while keeping ceilings VFR.




Short Term...KDW
Long Term...TWF
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