Area Forecast Discussion
Issued by NWS Jackson, KY

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966
FXUS63 KJKL 080600 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
100 AM EST Thu Dec 8 2016

.UPDATE...
Issued at 100 AM EST THU DEC 8 2016

The forecast remains on track. Did freshen up the hourly
temperatures and dew points, as temperatures have warmed up in the
eastern valleys, where decoupling had taken place earlier. There
are some weaker returns starting to show up on radar; however,
there are still no reports of flurries thus far. Will continue to
leave the mention in for now.

UPDATE Issued at 912 PM EST WED DEC 7 2016

High and mid level clouds moving across the area so far have been
too sparse to keep the southeastern Valley locations from
decoupling and dropping to around 30 degrees. The top of Black Mtn
around 4000 feet MSL has experienced an increase in dewpoints from
the single digits above zero to around 20 during the past hour,
however, model data and 0Z ILN and BNA RAOB suggests there is
still a dry layer between that level and about 7 to 10kft. Models
continue to suggest some moistening up of this dry layer as a
shortwave approaches overnight, possibly enough to support a few
flurries prior to dawn or around dawn falling from this mid deck
or high low cloud deck. Upstream over parts of central MO a few
flurry or very light snow observations have been noted over the
past hour. HRRR and short term models generally keep any very
light activity south of the I 64 or the Mtn Parkway and have it
diminishing as moisture again 850 to 700 mb moisture decreases
after dawn on Thursday.

Hourly grids have been freshened up based on recent observations
and short term model trends.

UPDATE Issued at 730 PM EST WED DEC 7 2016

Some mid and high clouds continue to drift overhead with light
generally northwest winds across the area as sfc high pressure
begins to build into the region. At upper levels, a closed low
was located over Ontario and the Northern Great Lakes region with
a couple of shortwaves in west to southwest flow approaching the
Lower OH Valley region. As the strongest of these shortwaves
nears, models do have an increase in moisture near and below the
dendritic growth zone and some omega in that layer later tonight
into early on Thursday although the air from about 850 mb to the
sfc is progged to remain rather dry. This scenario will be
favorable for lowering of the mid clouds toward the 5kft mark at
least briefly around sunrise and perhaps a few flurries. This is
in line with the previous forecast.

Hourly grids have been freshened up based on recent observations
and trends with little change overall being necessary at this
time.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 245 PM EST WED DEC 7 2016

Upper low north of Lake Superior will continue to move east
across Ontario, with trailing upper trough axis over the plains
shifting east. At the surface, cold high pressure will continue
to nose east into the Ohio Valley. The upper troughing and surface
ridging results in colder air working its way into KY, with lows
tonight mostly in the upper 20s and highs on Thursday from the mid
30s to around 40, about 10 degrees cooler than today. Even with
the trough shifting east, and the surge of colder air, there will
be very little moisture available. The outside chance for a few
flurries remains in the forecast for late tonight and early
Thursday.

Thursday night will be even colder than tonight, with lows in the
upper teens to lower 20s. Some clouds will affect the northeastern
part of the forecast area as a short wave trough swings by to our
northeast. The clouds are not expected until late in the night, so
temperatures should still fall off quickly in the northeast
Thursday evening. If the clouds move in earlier than expected
overnight lows would be warmer than current forecast in the
northeast. There is still an outside chance for a few flurries in
the northeastern part of the forecast area late Thursday night.

.LONG TERM...(Friday through Wednesday)
Issued at 318 PM EST WED DEC 7 2016

Models struggle right out the gate trying to capture strength and
timing of progressive features in a broad mean trough, or nearly
zonal flow pattern across the CONUS. First main shortwave
disturbance to deal with will track quickly out of the Pacific NW
and through the Plains, bearing down on the Ohio Valley region by
sometime Sunday, or possibly Sunday night into Monday. The 12Z
ECMWF is roughly 18 to 24 hours slower than the 12Z GFS with this
first system. The 12Z Canadian keeps the middle ground, showing
similar timing to the ECMWF while at the same time finding a way
to support the GFS by picking up on some energy into the area a
bit earlier on Sunday proper. The second main shortwave system to
affect our area, similar to the first with respect to its track
will drop into the region at the end of the extended window. The
ECMWF is considerably weaker with this shortwave than the GFS but
is similar in timing.

For sensible weather, temperatures remain seasonably cold to below
normal through the entire period. Models are still having difficulty
with the details of Sunday`s system and forecaster confidence is
low. This system appears to be trending slower overall. As such that
may provide enough time for the column to warm so that the bulk of
precipitation falls as rain. However, we still can not rule out a
little wintry mix at the onset of precipitation. For our second
system at the very end of the extended window, there is reasonable
agreement that this next system will be colder. Still way too far
out to say for sure, but this system may present our first real
chance at some accumulating snowfall. Time will tell.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 100 AM EST THU DEC 8 2016

VFR conditions look to hold on through the period. Clouds will
lower to the 6-8k feet agl range through 15z, before thinning out
through the rest of the day. Northwest winds of around 5 kts will
become west to northwest at around 10 kts by noon, with gusts of
around 15 kts at times. Winds will then diminish to around 5 kts
by dusk.

&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...SBH
LONG TERM...RAY
AVIATION...GEOGERIAN



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