Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 221722
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
122 PM EDT Sun Apr 22 2018

.UPDATE...
Issued at 102 PM EDT SUN APR 22 2018

The latest radar imagery showing the bulk of the returns remain
south across the Tennessee Valleys. The downslope flow across the
region is leading to a mix of sun and clouds this afternoon. Given
this did introduce a decrease in cloud cover into the forecast
particularly in the far east. Otherwise, more minor update to
better portray the latest trends in temperatures.

UPDATE Issued at 1020 AM EDT SUN APR 22 2018

An area of surface high pressure across the Great Lakes remains
our primary influence, with a lessening influence from weakening
upper level ridging. The greatest influence from diffluent flow
aloft remains to our south and think we will struggle to see rain
shower activity make much of the northward push today. The other
influence that will increase is the downslope flow and this will
further mitigate the precipitation potential across much of
eastern Kentucky today. The HREF probs lead to further confidence
of the drier trend, but the good news is the forecast reflects
this fairly well at this point. The best chances of seeing light
rainfall will be toward the Lake Cumberland region later this
afternoon. Only minor changes were needed to deal with the latest
obs and trend at this time.

UPDATE Issued at 810 AM EDT SUN APR 22 2018

Hourly grids were updated based on recent observations. However,
this led to no substantial changes.

&&

.SHORT TERM...(Today through Monday)
Issued at 440 AM EDT SUN APR 22 2018

Early this morning an axis of a shortwave mid and upper level
ridge extended northwest into the OH Valley from off the southeast
US Coast. Meanwhile a mid and upper level low was meandering in
the vicinity of Wichita, KAS, Enid and Stillwater, OK vicinity.
Convection was occurring to the east and southeast of the mid and
upper level low center. The associated surface low was over
Arkansas with a secondary surface low or wave near the TX and LA
Gulf Coast area. A warm front extended across southern AR,
southwestern MS to far southwest AL while the trialing wavy
surface cold front extended from southwest AR down near the TX and
LA border and into the Gulf of Mexico. Mainly high clouds and
some mid level clouds have been moving across the region
overnight. Mid level clouds are more numerous from southern IL and
western KY into western and middle TN and south from there into
the Gulf Coast states. East to northeast flow around surface high
pressure centered to the northeast and east of the area was
reinforcing dewpoints in the 20s for ridge and more open terrain
areas though dewpoints are currently locally higher in decoupled
valleys.

The mid and upper level low is expected to track southeast to near
Little Rock AR by sunset this evening and then move into
southwestern TN around dawn on Monday and then meander to be
centered northwest of Nashville by the end of the period. The axis
of the mid and upper level ridge will move east of the region this
afternoon and evening with the surface high departing to the
north and east. Moisture should increase through the day today,
more quickly at mid and upper levels than the lower levels. This
will be especially true over the east and northeastern sections of
the region where dewpoints are only expected to modify to the mid
and upper 30s this afternoon. This combined with highs near 70 to
the lower 70s should lead to min rh in the 20 to 30 percent range
across northeast and southeast regions of the KDF if not the 20
to 25 percent range over portions of the Kentucky River and Big
Sandy region. Locally, the pressure gradient is not expected to
increase ahead of the mid and upper level low and surface system
until this evening and tonight limiting fire weather concerns.
Isentropic lift should lead to some showers encroaching on the
Lake Cumberland region from the Cumberland Plateau and middle TN
and central KY region by sunset.

Moisture will continue to increase further tonight as the mid an
upper level system get closer to the region. However, drier air
to the north and east and even low level flow becoming downslope
should slow this progression and areas nearer to the WV border
will probably not experience anything more than sprinkles until
after sunrise on Monday. The pressure gradient increases further
on Monday and should be locally stronger over the higher terrain
near the VA border. With this in mind opted to go considerably
higher than than the blended model guidance for normal windier
locations such as Black Mtn and the Flatwoods area of Pike County.
In these locations sustained winds should reach into the 20 to 25
mph range with gusts as high as 35 to 40 mph. These winds will
have a downslope component as well so although measurable rain
should fall in most locations, though the downslope component
should cut back on QPF several miles downstream of Pine and Black
Mountains. Also, some limited insatiability will be present over
the far southwestern portions of the area where MUCAPE should
increase into the 250 to 500 j/kg range pending solar insolation.
Model blend probabilties for thunder also get into the isolated
to low end chance range here. Thus some thunder cannot be
completely ruled out and regional ISC consensus was to include
isolated thunder near the TN border out in the Lake Cumberland
Region on Monday afternoon.

.LONG TERM...(Monday night through Saturday)
Issued at 350 AM EDT SUN APR 22 2018

The extended period will begin as a upper level closed low
pressure system makes its way over the lower Ohio Valley,
bringing increased chances of rain showers through mid-week. This
will move to the northeast and out of the Commonwealth by
Wednesday afternoon. The models are in good agreement for this
first part of the long term forecast, but begin to deviate after
Wednesday. As the split upper level flow merges Wednesday night
into Thursday morning, a short wave looks to move through our area
which could bring chances for showers as well. This will quickly
exit eastern Kentucky, leaving most of Thursday dry. Models are
still in quite a bit of disagreement with timing and intensity of
a possible third system for Friday. The GFS is faster with this
system, showing a neutral trough moving over the OH Valley with
the potential for showers. The ECMWF shows a weak, positively
tilted trough with little moisture associated with it. Will
continue to monitor how this system develops for future updates.

As for temperatures for the week, high temps will remain in the
low to mid 60s for much of the week. The low temps will be in the
low 50s until Wednesday night. Low temps Thursday night will
decrease slightly to be in the low to mid 40s. This cooling trend
looks to continue for Friday night, with temps right around 40.
However, confidence is low due to model disagreement later in the
forecast period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 122 PM EDT SUN APR 22 2018

We remain under the influence of a surface high across the Great
Lakes but this will slowly move out of the picture. We are seeing
a mix of sun and clouds this afternoon and better moisture
remains to our south across the Tennessee Valley. This has been
aided by the downsloped flow that will continue to keep VFR
conditions in place across eastern Kentucky for the TAF cycle.
This has also slowed the progression of precipitation northward
and this trend will continue until later today into the overnight
hours. The better chances of seeing rain showers will be across
the Lake Cumberland region, but again these showers will remain in
the VFR range for VIS and CIGs.

&&

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

$$

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



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