Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 141401
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1001 AM EDT Mon Aug 14 2017

.UPDATE...
Issued at 1001 AM EDT MON AUG 14 2017

Based on radar trends and latest short range guidance have
updated NDFD. Showers will be most numerous in the north through
the morning, with the best chance for showers shifting to the
southwest and southern part of the forecast area this afternoon.
This latest forecast thinking has been depicted in the NDFD.

UPDATE Issued at 808 AM EDT MON AUG 14 2017

With the 06Z model run the NAM and GFS have come into better
agreement for the 1st period, and have made minor updates to the
forecast based on this. Unfortunately, the agreement falls apart
overnight, with the NAM once again being inconsistent and showing
convection with very heavy rain. The GFS has does not have the
heavy rain and has been consistent, and it was relied on much
more heavily for the forecast.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 458 AM EDT MON AUG 14 2017

A weak mid/upper level wave was approaching from the west
southwest early this morning. Radar was showing precip expanding
over south central KY in association with it, but with precip
originating at mid levels, much of the initial returns on radar
were probably still virga falling into drier air below. Will look
for moistening to eventually allow for precip today. Models all
show precip by day`s end, but there`s not good agreement on the
details. With MOS guidance giving at least likely POPs, have gone
with this over most of the area. However, it was a struggle as to
how to depict the details in the required one hour increment
grids. Weak instability also comes into play, and a slight chance
of thunder was used early this evening.

For tonight, have favored the GFS and ECMWF over the NAM. The NAM
has been very inconsistent in recent days, with sporadic runs
showing large amounts of precip at times (the latest one being
the 06z 8-14 run for tonight). Will forecast a general decline in
precip overnight. On Tuesday, diurnal destabilization may bring
another increase in convective precip. However, it the convection
would be fighting against an expected decline in deep moisture as
the wave aloft pulls out to the east. That being the case, have
only used low POPs.

.LONG TERM...(Tuesday night through Sunday)
Issued at 407 AM EDT MON AUG 14 2017

Upper level ridging will remain in place across the far SE conus
through the extended portion of the forecast. With a deep upper
level low across eastern Canada during much of the extended as
well, Kentucky will find itself in a troughing pattern, though
very deamplified due to the ridging to our south. Several waves
are expected to traverse through this longwave pattern and move
from west to east across the Commonwealth through the workweek
bringing unsettled weather. Models start to diverge in solutions
by the weekend, with the ECWMF developing a closed low over the
Great Lakes and longwave troughing across the eastern Conus during
the day Saturday, while the GFS is much weaker and slower in this
development, not impacting the region until Sunday. By Monday
they actually come back into agreement with a strengthening ridge
building in across the state.

At the surface, exiting high pressure to our east will allow for
more southerly return flow to make its way into the region for
Wednesday. This will interact with a weakening warm front just to
our south to produce shower and thunderstorms chances throughout
the day, mainly in the southern portion of the state. Meanwhile, a
surface low will be located across the central plains and Upper
Mississippi River Valley during the day Wednesday, moving
northeast and into the Upper Great Lakes by Thursday. This will
pull the above mentioned warm front farther northward and elongate
it across the state from north to south through the day Thursday
without much eastward progression as the parent low slows its
movement. The low will pick back up the pace by Friday and
continue farther NE, pulling the weakening warm front eastward
across the rest of the state and JKL CWA. It still looks as though
the warm front becomes a bit washed out by the time it makes it
across our CWA, but should still provide good convective
potential.

A cold front will be close on the heels of the warm front, making
it just NE of the Ohio River during the day Friday, and stalling
out through the day Saturday. It will finally push southward
across the state during the day Sunday, but with little impact.
High pressure will take hold for the remainder of the extended as
the stationary front remains just to our south.

Overall, all this boils down to is unsettled weather through much
of the extended, with near normal temperatures but humid
conditions thanks to the southerly flow from the Gulf. Best
chances for convection will be during the afternoon during peak
heating/instability, and best coverage should be during the day
Friday as the warm front shifts eastward across the region. The
cold frontal passage on Sunday will be quite weak, with generally
only isolated convection expected. However the boundary will
remain close enough to our south to warrant isolated pops across
the far SE for the daytime Monday as well. Otherwise much of the
CWA should be clearing with high pressure taking hold.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 808 AM EDT MON AUG 14 2017

Showers were affecting much of the area at the start of the
period, but were still not causing many restrictions. However, as
precip continues and the air moistens, will expect the areas with
the more persistent precip to drop to MVFR conditions for a while
today. Shower coverage should diminish this afternoon, but with
some heating and destabilization, a few thunderstorms could pop
up late in the day and this evening-- mainly in the southern part
of the area. By the end of the period, any showers should be
sparse. The only caveat is that there is some model discrepancy
for the upcoming night. The 06Z run of the NAM model shows very
heavy rain for the southern part of the area, but it is not
consistent with earlier runs. Have mostly discounted this, and
relied more heavily on the more consistent GFS model which has
decreasing showers.

&&

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

$$

UPDATE...SBH
SHORT TERM...HAL
LONG TERM...JMW
AVIATION...HAL



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