Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 280623
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
223 AM EDT Sun May 28 2017

.UPDATE...
Issued at 223 AM EDT SUN MAY 28 2017

Subsidence is building in behind the exiting rain/MCS. This will
provide a much needed dry period through the remainder of the
overnight period. A few showers could still skirt areas near the
Tennessee border, but this probably would not occur until after 4
am. As far as Sunday, does not look like much of a trigger through
the day as instability looks like it may be slow to recover with
much of the better moisture trapped to our south. We may not see
much until the front makes its move towards the area Sunday
evening. With that said, many of the CAMS do not really have much
for our area through Sunday night. Even the 00z NAM looks very
unimpressive with all the ascent and instability to our south with
the convection near the Gulf coast. Could still see a broken line
of showers or storms push through sometime during the evening, but
confidence is fairly low still. For the time being will continue
to back off pops. Also removed thunder late Sunday night into
Monday as instability is lacking behind the front.

UPDATE Issued at 1032 PM EDT SAT MAY 27 2017

The watch was allowed to expire on time, as the stronger
convection has made its way further southeast into Tennessee.
Moderate stratiform rainfall, with embedded thunder, will
gradually diminish across the southwest half of the area over the
next 1 to 2 hours. Some convection has fired up across north
central Kentucky, but this will likely die out before making it
much further east. Included areas of dense fog in the valleys,
with the thicker cirrus shield likely thinning out with time.
Updates have been sent.

UPDATE Issued at 921 PM EDT SAT MAY 27 2017

Storms are gradually weakening across the area, with mainly a
heavy rainfall/flash flooding threat to continue across portions
of the Cumberland Valley over the next few hours. Will likely be
dropping the watch on time. The latest HRRR and radar mosaic
trends suggest a quieter overnight, and given the lack of forcing
and the already worked over atmosphere, this seems reasonable.
Have trended down with the POPs into Sunday morning, before a
possible re-fire occurs tomorrow afternoon, although forcing still
may be on the weaker side. Will have to take a look at fog for the
overnight as well, with only weak southerly flow remaining in
place at the low levels and thicker debris clouds gradually
thinning out with time. Updates have been sent.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 429 PM EDT SAT MAY 27 2017

The latest surface map features a stalled frontal boundary aligned
from near the Ohio River back towards Oklahoma. Aloft, a
positively tilted trough, stemming from an upper level low
spiraling across Manitoba, is positioned from the northern Plains
down across the Four Corners region. A few short wave troughs are
traversing the more zonal flow in place along and east of the
Mississippi River.

Convection has fired up along the frontal zone to our north, as
well along some leftover outflow across central Kentucky. A short
wave trough is also moving through the eastern half of TN/KY,
helping to weaken the cap, that had held back convection through
the morning hours. Deeper and more organized convection has also
fired up back towards southern Missouri, where very prominent
instability exists.

The models have been very erratic with convective initiation and
the evolution of it over the next 24 hours. As such, the forecast
is lower confidence through Sunday.

Through this evening...scattered to numerous showers and
thunderstorms will continue to develop and move off to the east
and northeast. A few of these have already reached severe limits,
along with locally heavy rainfall with some cells training in
places. An overall diminishment is expected after 01 or 02z.
Later tonight, the higher resolution short term model guidance
suggests less of a widespread wind damage threat across eastern
Kentucky, as most of the CAMs are taking organized convection well
to our southwest. This seems reasonable based on the good Theta-E
gradient set up across southeast MO and western KY/TN, where the
better instability bubble exists. There may still be some outflow
generated convection into our area on the eastern flank of this
complex, so have broad-brushed a 50 POP across the area.

Most of the CAMS suggest very little redevelopment into Sunday
afternoon in the wake of the complex; however, if we do not see
much affect from the outflow, then the atmosphere may recharge for
the afternoon. The one issue will be forcing, as upper level
heights look mainly neutral, and the surface front will still be
located to our northwest. As such, have only included chance POPs
for the afternoon, but instability will be ample once again, so
anything that does go could approach severe limits.

The front will approach from the northwest Sunday night, bringing
another round of showers and thunderstorms. The severe potential
will likely be diminishing with the loss of instability, but heavy
rain will still be a concern.

.LONG TERM...(Monday through Saturday)
Issued at 345 PM EDT SAT MAY 27 2017

Precipitation will be exiting during the day Monday as a shortwave
moves east of the region along with a surface cold front, allowing
drier air to usher in behind. A secondary cold front is projected to
develop just west of our CWA during the day Tuesday, remaining
nearly stationary over the next 24 hours. A longwave trough axis
will also begin move through the state during this time. As such,
models are not in good agreement with the mesoscale features,
specifically the location and timing of precip developing with this
system. Went ahead and kept isolated POPs in for Tuesday afternoon
as daytime heating should help kick off some convection ahead of
this frontal feature. Pops will then increase across the SE into the
day Wednesday as the front finally starts shifting eastward across
the state. Did leave out thunder late Tuesday night as latest GFS20
forecast soundings were showing a hefty llvl inversion in place that
will inhibit instability. Showers and thunderstorms that develop
during the day Wednesday will taper off through the evening as the
frontal boundary passes through and a drier airmass moves in once
more.

High pressure and dry weather will remain in place through Thursday.
By Thursday night/Friday, a stationary boundary will likely set up
just south of the state, interacting with a potential upper level
shortwave that will move through the region during this time.
Although models are overall not in very good agreement about the
timing and placement of the mesoscale features, they do generally
agree that this will bring the return of shower and thunderstorm
chances to the state Thursday night into Friday, lingering through
the end of the forecast period Saturday as the boundary to our south
remains in place. Unfortunately the GFS and ECMWF are actually not
in good agreement about this feature during this time, though both
do produce the above mentioned precip, so stuck close to the blend
for this time period.

Overall there are only minor variations in the afternoon temps
during the extended portion of the forecast, with high temps
expected to range from the mid/upper 70s to near 80. Overnight lows
will generally be in the 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 223 AM EDT SUN MAY 28 2017

A tricky forecast overnight as some low stratus or fog may try to
form after the recent rain. In fact, KJKL already has a low cig
and KLOZ has one now. The other sites are still VFR. For now will
go IFR at these sites and go VFR elsewhere, but may need to amend
if the IFR conditions spread. Ceilings will go back to VFR on
Sunday and should stay that way through Sunday night. A cold front
will bring a threat of a few showers or storms Sunday evening, but
confidence in coverage is too low to include in TAFs at this
point.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through late tonight for KYZ050>052-058>060-
068-069-079-080-083>088-104-106>120.

&&

$$

UPDATE...KAS
SHORT TERM...GEOGERIAN
LONG TERM...JMW
AVIATION...KAS


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