Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 210009

Area Forecast Discussion
National Weather Service Louisville KY
809 PM EDT Sun May 20 2018

...Forecast Update and Updated Aviation Discussion...

.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...(00Z TAF Issuance)
Issued at 802 PM EDT Sun May 20 2018

Scattered storms ongoing this evening should stay away from most of
the TAF sites except for BWG. There will be chances for storms
moving through BWG through around 02Z or so. Thereafter, dry weather
with partly cloudy skies is expected through much of the night at
the TAF sites. Some light fog will be possible at BWG given that
area has received more rain today.

For tomorrow, showers and storms will continue to be the main
concern. Rain looks to move into the vicinity of HNB close to
sunrise. Storms then will likely develop from mid morning through
the afternoon hours. A PROB30 group for TSRA was included in the
TAFs for the most likely time of convection developing tomorrow.




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