Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 041018
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
518 AM EST Sun Dec 4 2016

.SHORT TERM...(Today through Monday)
Issued at 408 AM EST SUN DEC 4 2016

Light precip has encompassed our southern CWA and is continuing to
slowly work its way north as it overcomes a layer of llvl dry air.
Temperatures across the CWA are above freezing so far this morning,
so all precip should be falling as rain, even if some wet bulbing is
occurring. However, can`t rule out some of the higher
elevations(generally above 2k ft) still seeing some snowflakes mix
in as temperatures will be a tad bit cooler here at onset, and they
could possibly tap into colder air aloft as well. Overall, continued
to slow down pops through this morning based on the latest radar and
hi-res model trends. It also looks like there may be more of a break
into the afternoon, with a defined southern extent of rain pushing
eastward of the state, and a secondary northern extent moving in
after 21Z. Kept chance pops in otherwise during this time and into
the overnight. Between about 6Z and 10Z (starting in the east), dry
air really begins to pull in aloft as the upper level forcing starts
pushing east of the region and allows cooler drier flow into the
region. This will limit saturation to the lower levels, supporting
more of a drizzle event, before the dry air continues to quickly cut
off remaining precip potential by dawn Monday. Lows Monday morning
should remain just above normal, generally in the upper 30s across
the CWA.

Low level clouds will likely persist throughout the day Monday as
winds near the surface will be from a more NE to E direction
compared to the Wrly flow in the mid and upper levels, keeping
lingering moisture trapped near the surface for much of the day.

A strong upper level low located across TX during the day Monday
will begin to track northeastward as we head into the extended
portion of the forecast. As this occurs, expect another strong pull
of Gulf moisture into the Ohio Valley region, with a surface low
pressure system rotating across Louisiana. This will result in high
clouds building into the region once more from south to north
throughout the day Monday and will help boost temps to just above
seasonable normals in the afternoon despite cloud cover. While
precip chances should generally hold off until after 0Z Tuesday,
there is still a small potential that some pops could overcome mid
level dry air between 18Z Monday and 0Z Tuesday, mainly along the TN
border. As such, did include slight chance to low-end chance pops
here for this time frame.

.LONG TERM...(Monday night through Saturday)
Issued at 518 AM EST SUN DEC 4 2016

Models solutions are in reasonably good agreement with the
general mid/upper level pattern through the extended but
continue to differ significantly with details in the strength and
timing of several features embedded within an overall progressive
flow. This results in even larger differences in sensible weather
later in the forecast.

Mid/upper level cut off low moving out of Texas early in the
period opens up into a wave as it passes through the region
Tuesday. The GFS is slightly slower and stronger with this first
disturbance compared to the more similar ECMWF and Canadian. This
system will provide a soaking rain to the area with models
spitting out about an inch of rainfall on average, mainly from
Monday night through Tuesday. Forecast soundings do hint at some
marginal, very elevated instability Monday night. Mid/upper level
lapse rates do steepen a bit between about 10k and 22k feet. In
general CAPE remains below 100 J/kg. But there is substantial
shear within this layer as well, on the order of 30 to 50 kts. So
while one could not totally rule out a faint rumble of thunder,
feel the overall threat is low enough that any mention of thunder
was left out of the forecast for now. However, will pass on to
upcoming shifts for monitoring.

Forecast gets quite tricky thereafter as a series of disturbances
rotate around a low pressure system residing along the Northern
Tier and southern Canada. A shortwave trough swings through the
region sometime towards the end of the week, most likely
Thursday, as models present a range of possibilities with respect
to the timing and strength of this trough. Details of sensible
weather are not any clearer but the GFS and Canadian continue to
advertise a more similar solution with the ECMWF a much warmer and
wetter outlier, bringing a surface low and heavier precipitation
in the form of rain across the Commonwealth. The faster GFS
solution ushers colder air into the area at a much quicker pace
and hints at the possibility of some light isold to scattered snow
shower activity. The Canadian, being a colder solution similar to
the GFS keeps our weather dry. Until models begin to show better
agreement and/or show some solid trends will continue to rely
heavily on the model/guidance blends which suggest that a wintry
mix of precipitation will be possible through that time frame
depending on the time of day/night. On a more certain note, much
colder air does eventually move into the area for Friday and next
weekend. Thus any precipitation that does fall will transition to
just snow Thursday night into Friday with the potential of some
lingering upslope snow shower activity into early Friday morning.
Wouldn`t be surprised if future forecasts extend the snow shower
activity into Friday proper or even Friday night, as this is type
of scenario is typically handled poorly by the larger scale
synoptic models. At this point do not expect anything more
significant than minor snow accumulations at best, and if that.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 103 AM EST SUN DEC 4 2016

Very tricky forecast overnight and into the day tomorrow. A
mid/upper level wave is expected to impact the TAF sites through
the forecast period, however surface high pressure remains at the
surface with a layer of dry air in place in the low levels. IR
SAT does show high clouds penetrating eastern KY as the system
continues to approach, and should continue to stream across the
region overnight. These clouds are expected to thicken and lower,
but based on latest trends, this may occur a bit later than
originally expected. As of the 6Z TAF issuance, VFR conditions
are expected to persist through 12Z at the southern sites KSME and
KLOZ, but will quickly deteriorate after this point to MVFR
throughout the day as moisture finally overcomes the llvl dry
layer, and rain chances set in. This will occur a couple hours
later at KJKL and KSJS and closer to 18Z at KSYM. Llvl clouds will
linger throughout the upcoming night as well, possibly lowering
further to IFR, even as precip chances begin to taper off.
Overall, winds should remain light and variable throughout the
period.

&&

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

&&

$$

SHORT TERM...JMW
LONG TERM...RAY
AVIATION...JMW


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