Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 082155
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
455 PM EST Thu Dec 8 2016

.SHORT TERM...(This evening through Friday night)
Issued at 315 PM EST THU DEC 8 2016

Surface analysis reveals the strong Canadian high pressure remains
parked across the central portion of the country and we remain in
the middle across eastern KY. This has led to tighter isobars
and consequently we have seen west to WNW flow with gusts 15 to
20 knots. Also we have seen some CU develop this afternoon given
decent low level lapse rate and weak moisture at around the 850mb
level. The better coverage of Stratocu is placed to our north and
this will continue to spread SE through the evening and
overnight. Model soundings would suggest we also manage to get
some moisture into the dendritic growth zone and this will aid in
the potential for some flurries. Also given the better cloud cover
went really close to previous in trying to show overall higher
numbers low temp wise in the east and lower values across the
Bluegrass and Lake Cumberland region. Goes without saying that
Black Mountain will likely be the big winner with lower teens.

Friday the surface high pressure is expected to build east and
this will ease the pressure gradient across the region. Also upper
level winds will reduce overtime and lead to little influence from
afternoon mixing. Cold air will be maximized early Friday as 850mb
temps will be between -10 to -12C, and this will lead to one of
the coldest afternoons of the season with most not making it above
the freezing level. While 850mb temps begin to warm Friday night
the surface high will crest across the region. This will lead to
another night of teens and even lower teens for many including the
valley spots. The only issue would be some mid level clouds and
how they could lead to a slight dampening of temps. That said was
not willing to go much lower than the lowest COOP MOS number which
came in at 14 degrees.

.LONG TERM...(Saturday through Thursday)
Issued at 455 PM EST THU DEC 8 2016

The models are still in a state of discordance aloft through the
bulk of the extended resulting in a lower confidence forecast for
the overall period. Fast and near zonal flow will start out the
extended on Saturday before the pattern starts to amplify over the
High Plains on Sunday and the mid level energy rides east into
the Ohio Valley. The core of this next system passes to the north,
most amplified in the GFS, on Monday with more general fast zonal
flow to follow. Attention then turns to a very deep low building
over central Canada - most extreme in the GFS. This dominant low
then progresses slowly south and east. The GFS, and to a lesser
extent the ECMWF, bring a stream of energy through Kentucky and
the Ohio Valley on Wednesday. The lowest heights remain over the
area through Thursday in the GFS while the ECMWF`s heights
rebound more quickly. Given the outlier solution from the GFS will
favor a general model blend with a heavier lean toward the ECMWF,
but this situation will need to be followed closely due to the
potential of more southern interaction of the arctic jet stream
mid week.

Sensible weather will feature a dry and quiet start to the
extended as high pressure slides over the region and heads east.
This movement will allow for return flow from the southwest on
Sunday moderating temperatures. Deep sfc low pressure then takes
shape to our west and starts to come east on Sunday night and into
Monday morning. With this, and a warm surge of air that night,
rain showers are expected to spread over Kentucky by Monday
morning. The cold front passes through during the day and
temperatures are expected to fall in the afternoon. As such, a
chilly evening and night are on tap for Monday night with some
flurries or lingering snow showers possible - mainly in the
upslope areas and places closer to the Ohio River - though the
ECMWF would keep any ptype as liquid for the Cumberland Valley
into the evening and overnight. The forecast gets a lot more
complicated around mid week as the models diverge on the effects
of the northern stream deep low and leading edge of arctic air.
The GFS would shove the arctic boundary through around 12z
Wednesday with a potential change over to mixed pcpn and then snow
that morning - possible of significance. This solution has been
discounted for now, though, in favor of the more benign ECMWF
scenario. The latter forecasts moisture to seep north Tuesday
night and Wednesday while the coldest air holds off to the
northwest until later in the day and then the bulk of the
pcpn departs quickly - owing to the sfc low moving to the
Carolina Coast. Only that night would the air moving in from the
west be cold enough for a mix or snow just about as the moisture
exits to the east. Limited upslope flow with the ECMWF solution
would also keep the post frontal snow shower activity to a
minimum. Accordingly, the model differences keep confidence rather
low for specifics during the latter part of the extended and for
now have painted it more benign than the GFS extreme - but due to
the potential this situation will need to be watched and tracked
over subsequent forecast cycles.

Made only minor temperature adjustments to the CR grid init mainly
to allow for a nondiurnal curve Sunday night and Monday by using
the CONSRaw. Also adjusted PoPs down on Tuesday given excessive
influence from the unstable, of late, CMC forecast during this
time frame.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1225 PM EST THU DEC 8 2016

Much of the lower deck from this morning has scattered out and now
we are left with mostly high clouds across eastern KY. While we
have returned to VFR this afternoon Vis Sat and Obs are showing a
area of low MVFR building SE toward the region. These clouds will
stream in through evening and overnight and some snow
showers/flurries will also be possible. We have seen winds
increase out of the west at around 7 to 10 knots this hour and
would expect that to continue through the afternoon. Gusts will
generally be around 15 to 20 knots. These winds are still expected
to reduce through the evening.

&&

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

$$

SHORT TERM...DJ
LONG TERM...GREIF
AVIATION...DJ



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