Area Forecast Discussion
Issued by NWS Jackson, KY

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912
FXUS63 KJKL 092345
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
645 PM EST Sat Dec 9 2017

.UPDATE...
Issued at 645 PM EST SAT DEC 9 2017

The evening surface analysis shows a nearby cold front across
eastern Kentucky, with the parent surface low located across the
eastern Great Lakes region. In the upper levels, a trough axis
extends from the Ohio Valley into the Gulf of Mexico. These
features coupled with steep low level lapse rates and reasonable
omega within the dendritic growth zone are driving the light to
moderate snow bands we have seen this afternoon and evening. Much
of the moderate snow has now moved into far eastern and
southeastern Kentucky this hour, and the trends in the WSR-88D
composite are indicating this will continue to become more
scattered to isolated over the next few hours. This as the cold
front continues to usher in colder and drier airmass across the
Bluegrass State tonight. There does remain the concern of black
ice, as colder air helps to freeze residual moisture to area
roads and that has been highlighted in the latest SPS product.
Otherwise more minor updated were needed to deal with latest
trends in temps, dews, and winds.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 408 PM EST SAT DEC 9 2017

As of mid afternoon, an upper level trough extended from eastern
Canada south into the eastern Conus with an upper level ridge over
the western Conus. The center of the sfc low of a clipper system
is moving through the Great Lakes region with the associated cold
front trailing south into Central KY while the associated mid
level shortwave is approaching the region.

The clipper system will track into the eastern Great Lakes this
evening with the cold front moving across the area through early
this evening. Snow showers and flurries are ongoing and should
persist until after sunset as the colder airmass moves into the
region and lapse rate rates remain rather robust. The escarpment
in the Daniel Boone National Forest and the higher ridges of the
southeast part of the area should be most favored for very light
accumulations as winds become more of a favorable uslope
direction. Temperatures are currently in the mid 30s across many
areas of the eastern and southeastern sections of the area. With
marginal ground temperatures, most locations should not receive
more than a quarter to a half of an inch total from what has
already fallen and what falls this evening. Elevations above 2000
feet may receive a bit more than these amounts. Temperatures will
continue to fall and any light snow falling could initially melt
on some untreated surfaces before possibly freezing or becoming
slushy as additional snow showers pass resulting in slick or icy
spots. An SPS has already been issued to handle this. The low
level moisture will become shallower starting around 0Z or 1Z or 7
or 8 PM ESt in the western part of the area and then gradually
become shallower from northwest to southeast. Enough low level
moisture may linger long enough near the VA border so that
flurries could linger until almost sunrise on Sunday. Low clouds
should linger most of the night in many locations so ridgetops and
far western locations with partial clearing will be coldest for
overnight lows as coldest of the airmass moves through the area
tonight.

Mid level height rises will already have begun overnight behind
the departing shortwave while surface high pressure begins to nose
in from the Southern Plains. Mid level heights should rise further
on Sunday with surface high pressure building across the Gulf
States. Low level moisture and clouds is expected to diminish on
Sunday morning, but additional shortwaves passing to the north
should lead to bands of mid and high clouds on Sunday. This and a
relatively cold airmass still in place will lead to continued cold
temperatures.

Dry weather will linger into Sunday night and with general mid
level height rises and sfc high pressure centered to the southeast
at least a moderate ridge/valley temperature split from the
nocturnal inversion will be possible. COOP MOS guidance indicates
this, but blended model guidance was more uniform. Opted to not go
as low as the COOP MOS guidance just yet as the gradient could
lead to some mixiness and although there will be periods of mostly
clear skies, band of mid and high clouds aren anticipated and
guidance has an increase in moisture around 850 mb and below so
low clouds will also be possible.

.LONG TERM...(Monday through Saturday)
Issued at 230 PM EST SAT DEC 9 2017

The pattern will remain unchanged into next week with persistent
upper level troughing over the eastern US with a series of weak
clipper systems cross the great lakes and Ohio river valley.
Models continue to advertise all of these clipper systems will
struggle to bring much in the way of measurable liquid to eastern
Kentucky. However, much like the system today, any of these
systems may be capable of a quarter of an inch of snow. The first
clipper system looks to come on through Monday night into Tuesday,
with another one pegged for late Wednesday or Thursday.
Temperatures will remain below normal through next week, although
we could start to rebound a bit heading into next weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 615 PM EST SAT DEC 9 2017

The period is beginning with a wide variety of restriction
levels, as light to moderate snow showers move eastward across the
region. The more robust showers continue to move off into the far
east and the overall coverage of snow is lessening across central
Kentucky. This will be the trend as drier air filters into the
region behind the cold front tonight. Given the on going light
snow have been most robust restrictions with VIS in the IFR range
for most sites. The TAFs will come back to VFR through the
evening into tonight as the drier air filters into the region and
snow tappers off. The winds have been gusty this evening around 20
to 25 knots at times, but these will lessen through the night,
but the winds will generally remain out of the west.

&&

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

$$

UPDATE...DJ
SHORT TERM...JP
LONG TERM...KAS
AVIATION...DJ



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