Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 161612 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1212 PM EDT Wed May 16 2018

.UPDATE...
Issued at 1212 PM EDT WED MAY 16 2018

Made a few adjustments to the forecast based on trends observed in
the latest obs, surrounding radar imagery, and model data. Decided
to remove precipitation chances from the majority of the forecast
area for the next couple of hours, before bringing isolated to
scattered showers and storms back into the area by the middle of
this afternoon. Also removed some outdated morning wording from
the zone forecast text product. The updated forecast has already
been issued.

UPDATE Issued at 750 AM EDT WED MAY 16 2018

Hourly grids were updated over the past hour based on recent
radar and observation trends. This led to some adjustments to pops
west of JKL near sections of the Daniel Boone NF for showers or
even a thunderstorm. Coverage of showers and thunderstorms is
still expected to peak from mid afternoon through the evening
hours.

&&

.SHORT TERM...(Today through Thursday)
Issued at 439 AM EDT WED MAY 16 2018

Early this morning a shortwave trough was upstream of the region
near the confluence of the OH and MS Rivers while an upper low
continues to meander into the southeast. At the surface, a frontal
zone was in place from the mid Atlantic states west across the
Appalachians and then southwest near the OH River and eventually
west into the Plains. Showers and thunderstorms have lingered
nearer to the boundary in the northwest counties overnight with
rain rates and lightning having decreased over the past couple of
hours. Additional stray showers were moving across portions of
the Cumberland Valley. Several outflow boundaries likely also
remain across the region from convection on Tuesday and Tuesday
evening.

An upper level trough with an axis from the lower OH Valley into
the southeast will continue to develop today as these the upper
low and shortwave begin to interact. The axis of this trough
should move slowly east through the period. Meanwhile the wavy
surface front should sag a bit further south through this evening
and then further south and southeast near the crest of the
Appalachians through the end of the period. Moisture will
continue to remain abundant with values generally between 1.3 and
1.5 expected across the area today, increasing to about 1.4 to
1.7 tonight and then increasing to about 1.7 to 1.8 on Thursday as
deeper moisture associated with the upper level low that was
moving into the southeast works into the region.

Steering winds will remain weak today. A shower or thunderstorm
cannot be completely ruled out at any point. This afternoon,
instability expected to be sufficient for scattered to numerous
showers and thunderstorms to develop, especially near the front
in northern and western parts of the area as well as near the VA
border. The storms will be slow moving due to weak winds aloft and
any thunderstorms could produce locally heavy rain with the risk
of isolated instances of high water or flash flooding. This would
be especially true in locations that experienced heavier rainfall
over the past 24 hours. The strongest storms might also be
capable of producing gusty winds and small hail. These threats
will be included in the HWO.

Coverage of convection should wane through the evening. However,
with the front slowly sagging south across the area and a mid and
upper level trough in place, showers or even a thunderstorm will
remain possible overnight. With even higher PW on Thursday,
locally heavy rain is possible with chances possibly increasing
with the axis of the trough nearer to the region. Chances for
showers and storm are expected to peak on Thursday afternoon and
early evening. The heavy rain threat will continue to be mentioned
in the HWO.

.LONG TERM...(Thursday night through Tuesday)
Issued at 358 AM EDT WED MAY 16 2018

The upper level pattern for the extended begins with northern stream
ridging over the Great Lakes and southern stream troughing over the
OH Valley and southeastern CONUS. At the surface, a boundary will be
slow moving during this time. However, it will be the source of lift
and flow of warm/moist air brought up from the Gulf, which will aid
in the production of rain showers through Saturday. Modest
instability is present for Friday, so afternoon/evening storms are
possible. This pattern will hold until Sunday when weak ridging
develops over the OH Valley, bringing a brief lull in precipitation
at least until the afternoon. A shift in the overall flow will
follow for early Monday when a surface low pressure over the Plains
makes its way eastward. A cold front will advance towards Kentucky,
increasing rain chances for the beginning of the work week. The
better instability looks to be during this time frame as well, so
afternoon/evening storms will be possible through Tuesday.

Temperatures will be in the upper 70s to low 80s on Friday. Temps
will then warm up to be in the low to mid 80s through the forecast
period, with Sunday being warmest. Low temps will generally be in
the low 60s, but with some clearing and southerly flow Saturday
night into Sunday morning, valley temps could drop lower than the
ridges.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
ISSUED AT 800 AM EDT WED MAY 16 2018

A slow moving front is expected to push slowly south across the
area area through the period. A few stray showers and even a
thunderstorm were ongoing west of JKL at this time though this
activity is currently not affecting the TAF sites. Outside of this
and some patchy initial fog VFR is in place across the region.
Changes for showers and thunderstorms will remain, particularly
18Z to 3Z. Uncertainty remains in the timing and details for any
one location so have opted to continue with VCTS in the TAFs
starting generally near 18Z. With the boundary across the area and
a mid level trough in place convection cannot be ruled out from
that point through the end of the period so several hours of VCTS
was used. Any direct hit from a shower or thunderstorm would bring
a period of MVFR or even IFR visibility. Also, as the boundary
slips south, chances for low clouds and fog will increase with
some MVFR to IFR vis possible.

&&

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

$$

UPDATE...AR
SHORT TERM...JP
LONG TERM...CGAL
AVIATION...JP



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