Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 230907

National Weather Service Jackson KY
507 AM EDT Mon Apr 23 2018

.SHORT TERM...(Today through Tuesday)
Issued at 445 AM EDT MON APR 23 2018

The axis of mid and upper level ridging will continue to depart to
the east and northeast of the area today with sfc high pressure
also moving further northeast of the area. This will allow the mid
and upper level low currently centered near the Memphis TN
vicinity to meander into middle TN this evening and then reach the
Southern Appalachians by the end of the period. Moisture has
already been increasing across the area, especially aloft.
However, the flow from around 800 mb to the surface is downslope
which is slowing down increases in dewpoints and rh at low levels.
Despite this, showers or light rain has been falling across the
southwest part of the area overnight from a mid cloud deck in a
band east of the center of the mid and upper level system.

Today, the model consensus is for a band or bands of showers
to continue moving north and east across the area through mid
afternoon. Toward midday activity will likely become more isolated
to scattered in nature over southwestern counties. At the same
time, temperatures aloft should begin to cool. Thus with daytime
heating especially in the southwest part of the area additional
activity is expected develop by late afternoon or early evening
while a drying trend over much of the northern and eastern
sections from mid afternoon into the evening. Enough instability
may be present in fact for some isolated thunder to extend into
the Lake Cumberland region and possibly as far east as Whitely and
Bell counties or approximately where the SPC general thunder
outlook extends.

Momentum transfer in bufkit from the NAM has gusts into the 20 to
25 knot range from late this morning into this afternoon for many
area with up to 30kt possible, especially behind this band where
some limited solar insolation may add to the mixing. Gusts on top
of Black and Pine Mountains, the Log Mountains of Bell County and
the Flatwoods area of Pike County may reach as high around 35 kt
from late morning into the afternoon. The southeast downslope
component of the flow should lead to a rain shadow downwind of
Pike Mountain across portions of the southeastern counties and
downward adjustments were made to the initialized superblend qpf
in those areas to account for this. The downslope flow should also
lead to locally warmer max T in valley locations such as Harlan
and Cumberland, Whitesburg and Cumberland northeast to Dorton and
Elkhorn City where upper 60s to near 70 are anticipated.

Locations closer to the center of the upper level system and less
influenced by downslope flow especially from I 75 west should
experience more persistent showers through the evening into the
over night hours while some southeastern locations may be rainfree
for much of the night. A qpf trend which should begin during today
should continue into tonight with qpf twice or more times greater
in some of the southwest and western sections compared to the
southeast. Chances for showers should increase into central
portions of the area late Monday night as a band of showers is
expected per model consensus.

This band of showers should continue progressing north and
Northeast across the area into Tuesday afternoon. The coldest
temperatures over the next couple of days at 850 mb should be
during Tuesday morning into Tuesday afternoon. Steepening low
level lapse rates may lead to diurnal uptick in the rain rates
from the showers on Tuesday in the initial band with an isolated
thunderstorm or two also possible. Some redevelopment of showers
or even a thunderstorm or two may develop closer to the center of
the mid and upper level system on Tuesday afternoon.

Diurnal ranges will be much more limited than recent days through
the near term period with highs generally in the low to mid 60s
and lows tonight generally in the low to mid 60s. These readings
will be below normal for highs which are around 70 for this time
of year while lows will be a few degrees above normal as compared
to normal lows for this time of year in the mid and upper 40s.

.LONG TERM...(Tuesday night through Sunday)
Issued at 405 AM EDT MON APR 23 2018

A 500mb low will be collocated with a surface low pressure system
across Kentucky starting out at 0Z Wednesday. This will continue to
shift eastward out of the state throughout Tuesday night and into
the day Wednesday, with pops/rain chances expected to be on a
decreasing trend during this time. Upslope flow will keep some
chance pops in place through the day Wednesday, especially across
the SE, but additional QPF will be under a tenth of an inch through
0Z Thursday.

Models then lose considerable agreement by 0Z Thursday, with the NAM
and GFS planting a developing closed low over the south/central
Plains, and the ECMWF showing a strong closed low over the northern
Ohio Valley and southern Great Lakes region with a shortwave trough
over the central/southern Plains instead. The ECMWF shows this
closed low shifting SE across Ohio Wednesday night and into the day
Thursday, while both the GFS and ECMWF show the other shortwave/low
system tracking just south of Kentucky into the deep south during
this time. Surprisingly, which ever model pans out, neither actually
pulls precip from either system into the state, so will keep
Thursday dry in the forecast. Models then come into much better
agreement for another system which will affect the region to end out
the workweek.

A 500mb shortwave will follow deep troughing across the region,
deepening the trough as the axis moves through Kentucky Friday night
into Saturday morning. At the surface a cold front is expected to
shift from west to east across the state during the day Friday and
into Friday night, bringing with it a swath of chance pops.
Instability is still lacking, so will not include any mention of
thunder at this time. In fact soundings are actually quite dry, so
not expecting much QPF from this either. Even after tweaking QPF up
slightly from the Superblend, still only have well under a tenth of
an inch for the duration of the system.

During much of the extended period, temperatures will actually
remain relatively uniform, with highs in the low to mid 60s and lows
in the 40s. However, if clearing occurs overnight Friday night and
Saturday night (coupled with light winds), some sheltered valleys
may fall into the upper 30s. Ridging will slowly take hold
throughout the day Sunday and continue into Monday. This will allow
temperatures to climb into the low 70s both days.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)

An upper level low will meander into western TN through the
period. For much of the period the region will maintain a
downslope component of the flow with lower levels slow to
saturate. Thus mainly mid level clouds are expected through about
12Z with some low clouds thereafter but still in the VFR range.
Some brief MVFR is possible in showers or any thunderstorms across
western and northwestern sections of the area after 12Z, but vis
should remain 6SM or higher through the period. Winds should
increase to near or in excess of 10KT at the TAF sites during the
first 6 hours of the period out of the east southeast to




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