Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 191810
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
210 PM EDT Wed Apr 19 2017

.UPDATE...
Issued at 210 PM EDT WED APR 19 2017

Scattered showers continue to develop across the area this
afternoon. Am finally seeing a few strikes showing up as well.
Temperatures, and grids in general were in good shape. Bottom
line, few if any changes to the early afternoon update.

UPDATE Issued at 957 AM EDT WED APR 19 2017

Forecast is in pretty good shape this morning. An area of
scattered showers is slowly tracking off to the east. Additional
activity is beginning to fire further west now that diurnal
heating has begun to destabilize the boundary layer. A few
thunderstorms can not be ruled out either. Updated the zones to
freshen up wording and to remove morning fog. Grids have been
updated as well to bring them in line with recent hourly trends.

UPDATE Issued at 629 AM EDT WED APR 19 2017

Scattered to numerous showers continue to move ENE across the
region this morning based on the latest WSR-88D scans. These are
being provided to us by modest LLJ and dampening upper level short
wave seen in the mesoanalysis. That said, did opt to raise POPs
across portions of the region but still wane these through the
afternoon. Otherwise more minor updates were needed to deal with
latest obs and trends.

&&

.SHORT TERM...(Today through Thursday)
Issued at 335 AM EDT WED APR 19 2017

Surface wise, what was left of the boundary that was south of the
region yesterday has now lifted well north of the region. The is
leading to southeast flow across the region. The satellite trends
have showed the mid level deck that had eroded with some drier mid
level air is filling back in. This is likely do to a developing
LLJ at around the 850MB layer and dampening upper level wave, as
LVX VAD Wind profile shows around 30 knots near this level
bringing credence to the model guidance. Along with the cloud
cover development the WSR-88D radars are showing mostly isolated
showers across the eastern side of the state, while a more robust
area of showers has developed across central portions of the
state. The HRRR has been all over the place overnight into the
morning in how this evolves and not much help has been gained from
much of the other guidance. Therefore, took a middle of the road
approach in the grids. This will keep most of the area in
scattered coverage through the early afternoon and overall
coverage in then expected to wane by around 22Z. That said, hold
off thunder till this afternoon, as better instability will be
possible with MUCAPE values climb into the 500 J/kg range, but the
winds will be light aloft making this more garden variety activity.

Tonight thinking many spots will see a break in the showers and
possibly a break in the clouds. Did opt to lower the valley temps
and keep patchy fog going given the possible clearing/low level
moisture from afternoon convection. By Thursday do keep shower and
even afternoon thunderstorms in the forecast, as we remain in the
warm sector ahead of the next synoptic boundary. Given the lack
of surface lifting keep the better coverage along the higher
terrain near the VA border. Otherwise well above normal
temperatures are on tap, with highs climbing into the upper 70s to
lower 80s for most.

.LONG TERM...(Thursday night through Tuesday)
Issued at 447 AM EDT WED APR 19 2017

Overall, there is good model agreement during the period. At the
onset, a cold front will be entering KY from the northwest, and
crossing the JKL forecast area Thursday night. It is expected to
bring at least scattered showers and thunderstorms. The front will
stall to our south, and remain in close enough proximity for an
ongoing potential of precip on Friday. During the day Friday, low
pressure will be taking shape over the southern plains. This will
be in response to an upper level wave (emanating from the upper
low currently off the Pacific Northwest coast) moving southeast
toward that region. The low pressure system will track eastward
and draw the frontal boundary back north toward southeast KY
Friday night and Saturday. The GFS has trended further south with
the eventual low track since yesterday, and is similar to the
ECMWF which has remained nearly steady. This track takes the low
near the KY/TN border, resulting in a wet start to the weekend,
with a temperature contrast across the JKL forecast area. Rain is
a good bet everywhere on Saturday. Thunderstorms will also be
possible near the passing low, with surface based instability
possible in far southern KY, and elevated instability further
north. Heavy rainfall could be a concern, with the GFS and ECMWF
both showing some 2"+ amounts Saturday/Saturday night. Subsequent
models runs should provide more confidence as to if and where an
axis of excessive rainfall occurs. Significant rain should be
pulling out with the departing low by Sunday, but some light rain
could linger. Ridging at all levels then builds in on Sunday
night and brings decreasing clouds, with fair weather lasting
through the rest of the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 210 PM EDT WED APR 19 2017

Scattered showers continue to develop across the area this
afternoon. Am finally seeing a few strikes showing up as well.
Went with a general VCTS at all of our terminals until early
evening as activity should die down with loss of diurnal heating.
Only restrictions might be a very temporary drop to MVFR VSBYS in
any thunderstorms should they pass directly over a terminal.
However, with such widespread coverage decided to keep VSBYS
predominantly VFR. Guidance suggests we may see some light fog
early morning Thursday with some high end MVFR VSBYS, but decided
to keep more optimistic VFR VSBYS for now. Winds will generally
be light and variable except in and nearby thunderstorms. Gradient
winds pick up from the southwest Thursday around 10kts with
higher gusts to about 18kts as a cold front approaches the region.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

UPDATE...RAY
SHORT TERM...DJ
LONG TERM...HAL
AVIATION...RAY



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