Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 240501
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
101 AM EDT Wed May 24 2017

.UPDATE...
Issued at 101 AM EDT WED MAY 24 2017

A wave continues to move across the region with multiple waves
riding through the flow seen on mesoanalysis and WV SAT. It does
look like we will see a relative lull in showers until we move
closer to dawn when the surface low deepens. Made some adjustments
to POPs with the latest obs and trends otherwise a standard
update of the obs was done.

UPDATE Issued at 1055 PM EDT TUE MAY 23 2017

Hourly pops have been updated based on recent radar trends.
Showers and even a rumble of thunder in the far southeast has
occurred in the last hour as a mid level disturbance works through
the area. The current round of showers should weaken and shift out
of the area over the next couple of hours. However, another
disturbance should bring another round of showers and perhaps a
thunderstorm encroaching on the area around dawn.

UPDATE Issued at 835 PM EDT TUE MAY 23 2017

Some late afternoon heating and a mid level disturbance have
combined to bring some showers and thunderstorms to parts of
Central KY and parts of Middle TN and the Cumberland Plateau of
TN. Much of these have experienced a downward trend in intensity
over the past hour or so with the exception of the convection in
the Bluegrass Region of KY while showers persist across much of
southeast KY. Thunder chances were added for the evening with the
upstream thunder detected. Also, dewpoint depressions across much
of the area are just a few degrees. With low level moisture
lingering and some cooling in between the current shortwave and
the next to approach late tonight and on Wednesday at least some
patchy fog will be experienced possibly both on the ridges and int
the valleys and this has been included. Otherwise, no substantial
changes were needed at this time.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 500 PM EDT TUE MAY 23 2017

20z sfc analysis shows a broad area of low pressure over the
middle of the Tennessee Valley encompassing Kentucky. This has
brought showers and sprinkles to eastern Kentucky as well as
plenty of clouds. The rain has also kept temperatures in check and
on the cool side through much of the JKL CWA with readings
currently in the low 70s northwest and southwest where the clouds
were thinnest to the mid 60s in the rain further east. Dewpoints
are generally in the upper 50s to lower 60s while the winds are
light and variable.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict a deep and cut off
closed low digging into the Deep South through Thursday morning
along with ample energy swirling around. The core will roll down
the backside of this larger trough and generally target locations
to the south of Kentucky on Wednesday into Wednesday night. The
good model agreement lends support to a blended model solution
along with the use of the high res HRRR through the near term.

Sensible weather will feature scattered showers departing to the
northeast this evening - with a stray thunderstorm possible. This
will be followed by a lull in the activity through midnight for
most locations under cloudy skies before the next surge in
moisture moves in late tonight with showers and thunderstorms
increasingly possible toward dawn. The thick clouds should keep
most of the fog at bay tonight, but for places that saw the rain
late this afternoon and into the evening - should the clouds thin
enough - patchy fog will be possible and will need to be
monitored. Showers and thunderstorms will then sweep over all of
eastern Kentucky on Wednesday with some gusty winds and a window
of heavier rain possible should they manage to be more organized -
perhaps helped from a mid level wave swinging through around
midday. Have highlighted this time frame in the grids for the
best shot at thunder, as well. Later in the day the thunder
chances fade out from west to east as the main sfc low lifts past
to the east. Lighter shower will linger, though, into the night.

The CONSShort and ShortBlend were used as a starting point for
the grids` with only minor adjustments to temps through the
period. As for PoPs, made some significant adjustments to them to
better represent the spatial and timing aspects of the rain
shield moving into East Kentucky from late tonight through
Wednesday afternoon.

.LONG TERM...(Thursday through Tuesday)
Issued at 400 PM EDT TUE MAY 23 2017

An upper level low will be centered over Kentucky to start out the
period Thursday morning, shifting northeast throughout the day and
into Thursday night, with rising heights expected across the
Commonwealth. Ridging will take hold Friday, however will be
dampened as several shortwaves move through the pattern and affect
the region over the next couple of days. By Saturday, another upper
level low will drop south from central Canada, allowing for longwave
troughing to develop across the central U.S. While timing on this
system is still somewhat unresolved between the models, as is the
intensity of the trough, much of the state can expect some type of
height falls and destabilization to occur to round out the weekend
and start the beginning of the workweek. Models actually come back
into better agreement by the very end of the extended period, with
the axis of the trough nearing the state Tuesday, and traversing the
state into the day Wednesday.

At the surface, the presence of a surface low pressure system just
north of the CWA (in conjunction with the upper level low) will
result in precip chances throughout the day Thursday. This precip
will pull northeast of the region into Friday morning as the surface
low exits in this direction. However, given our location on the
backside of the cold front, latest forecast soundings aren`t
supporting much in the way of instability, so chose to keep out
mention of thunder Thursday. A brief area of high pressure will move
into place with the building heights, keeping us mostly dry Friday.
However, incoming shortwaves that will ride along this pattern will
bring the return of unsettled weather and shower/thunderstorm
chances by Friday night, continuing through Saturday and increasing
in intensity and coverage by Saturday night into Sunday as a surface
low moves NE towards the state and a cold front drags eastward. This
cold front will cross eastern KY Sunday night into Monday, with
another brief area of high pressure moving in behind during the day
Monday. Yet another cold front will near the state Tuesday,
attached to a stronger surface low to our north (in conjunction
with the second upper level low referenced above). This will bring
yet another round of precip (showers and thunderstorms) to the
region through the day Tuesday.

Temperatures should start out below normal during the day Thursday
behind the departing cold front, with highs in the mid 60s. stronger
S to SW flow will take place by Friday, bumping temps into the mid
and upper 70s Friday afternoon, and into the upper 70s and low 80s
on Saturday and Sunday afternoon. Despite a cold front moving
through on Sunday night/Monday morning, temps will only be slightly
(a couple degrees) cooler on Monday and Tuesday than the weekend
thanks to the quick return of SW flow behind the frontal passage.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 820 PM EDT TUE MAY 23 2017

In advance of a shortwave, areas of showers and thunderstorms are
moving across East KY this evening with the strongest activity
headed toward the far northwest counties and could affect SYM with
MVFR or IFR for a time. Additional showers could affect LOZ and
SME as well. This activity should diminish 3Z to 5Z before showers
increase again 10Z to 16Z. The low levels remain moist so outside
of showers some MVFR fog should develop and could affect all of
the TAF ties. This next round should lead to saturation at all
levels again and cigs should fall to MVFR if not IFR at times as
shra and some tsra move in from the southwest with the next
shortwave. Winds should average less than 10KT through the period.

&&

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

$$

UPDATE...DJ
SHORT TERM...GREIF
LONG TERM...JMW
AVIATION...JP



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