Area Forecast Discussion
Issued by NWS Jackson, KY

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744
FXUS63 KJKL 150614 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
114 AM EST Fri Dec 15 2017

.UPDATE...
Issued at 114 AM EST FRI DEC 15 2017

Have freshened up the hourly temperature and dew point trends
through the overnight, otherwise the forecast generally remains on
track.

UPDATE Issued at 1046 PM EST THU DEC 14 2017

The low clouds look to hang tough overall through the night, as
the latest short term model guidance shows plentiful moisture in
the 925-850mb layer pivoting back in across eastern Kentucky.
There are some spots that have seen clearing, mainly on the
northwest and southeast fringes of the deck. Have adjusted lows
accordingly, keeping mainly upper 20s to around 30 degrees for
locations where the clouds will not relent, while allowing for
some low to mid 20s in the cooler spots. Updates will be out
shortly.

UPDATE Issued at 723 PM EST THU DEC 14 2017

Latest GOES-16 imagery continues to show quite a bit of cloud
cover holding across much of eastern Kentucky. NAM Bufkit
soundings show this moisture quite well and actually show some
redevelopment through the overnight hours. A subtle shortwave will
also push in late tonight with some low level cooling noted. This
may be enough to bring the top of the moist layer into the -10 to
-12C isotherm allowing for some ice introduction into the clouds.
 This combined with a light west wind develop towards daybreak,
 may provide a bit of upslope into the higher terrain. All of this
 together points towards a good potential for some flurries or
 very light snow showers. Opted to keep precipitation non-
 measurable at this point, but some of the higher peaks in
 southeast Kentucky could see a light dusting by daybreak Friday.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 357 PM EST THU DEC 14 2017

Low stratus has held strong across eastern Kentucky this afternoon
in a post-frontal airmass. Temperatures have subsequently held
steady with current readings spanning the 30s. Surface ridging
building into the lower Ohio Valley and western reaches of the
Appalachians will keep light upslope flow in place through much of
the night as low-mid level moisture remains trapped beneath a
subsidence inversion. Have therefore warmed overnight low
temperatures a few degrees from the previous forecast given the
greater amount of expected cloud cover. Readings should generally
bottom out in the low-mid 20s, with perhaps a few valleys across
portions of northeast Kentucky flirting with the 20 degree mark if
any breaks in the clouds can occur nearer the core of the surface
ridge.

Yet another upper trough and associated surface low will rotate
through the Great Lakes Friday, keeping below normal temperatures in
the offing. Highs look to warm into the mid 30s, resulting in a
similar overall feel to Thursday afternoon. The lack of any bonafide
moisture recovery and northward displacement of the greatest forcing
will negate the threat for precipitation throughout eastern
Kentucky. Surface ridging nosing in from the southwest later in the
day will keep winds southwesterly and preclude a significant change
in airmass.

Following what may be a quick valley dropoff in temperatures Friday
evening/early night, an increasing pressure gradient downstream
of a surface low pushing into the upper Midwest will promote warm
air advection spilling into the Bluegrass and Lake Cumberland
regions. Temperatures by daybreak Saturday should therefore bottom
out a few degrees warmer than those seen Friday morning.

.LONG TERM...(Saturday through Thursday)
Issued at 322 PM EST THU DEC 14 2017

The extended portion of the forecast begins on Saturday with the
upper level pattern transitioning to a more progressive and less
amplified flow aloft. With a brief bout of ridging quickly passing
through on Saturday. In fact, with southerly flow reengaging on
Saturday, high temps will rebound into the 50s with clear skies in
place thanks to the mentioned ridging in place. The pattern east
of the Front Range displays a northern and southern portion of the
jet stream and rather zonal. However, a strong wave over the
southern stream develops over the southwest and moves into the
lower MS Valley into Saturday night. This feature then lifts
northeast into the OH Valley for Sunday morning and into the day
on Sunday bringing a modest round of moisture. Another weaker
wave tracks across the northern stream into the Great Lakes at
this time as well. This will keep a decent round of precip over
the area for Sunday and Monday. Concerning the Sunday morning
onset, model profiles indicate the possibility of the lower
profile wet bulbing due to evaporative cooling to freezing
temperatures at the surface leading to a possibility of a sleet
and or snow mix for a very brief period of time. However, latest
trends have showed a later arrival time of precip, this combined
with the time needed for the lower levels to saturate, will
likely lead to an all rain event at this time with a few instances
of snow mixed in. Rainfall, while still entering this event with
dry conditions will accumulated roughly less than a quarter inch.

After passage, another weaker wave along the northern stream will
pass through the OH Valley on Monday with a slight chance of
precip remaining into Monday night. Even so, temps will be above
normal for this time with the lack of amplitude in the pattern and
will only expect liquid precip. By Tuesday, another wave develops
out of the southern stream and lifts northeast bringing another
chance of precip into eastern Kentucky but with warmer air in
place, this event too will be all rain. Despite some rain expected
for Sunday through Tuesday, the lack of consistency in the models
leaves more to be desired and the overall dry conditions across
the area going into these events will be good chance pops at best.
In fact, the super blend cam in dry for the last day of the
extended on Wednesday so will go with that solution.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 114 AM EST FRI DEC 15 2017

A stratocu deck will expand and gradually lower down to MVFR
levels across the area through around dawn. This deck will then
raise up and dissipate by the mid to late morning hours, with VFR
conditions prevailing thereafter. Light and variable winds through
the late morning, will become westerly at 5 to 10 kts, with some
gusts of 15 to 20 kts at times, in the afternoon.

&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...GUSEMAN
LONG TERM...SHALLENBERGER
AVIATION...GEOGERIAN



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