Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 100541
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1241 AM EST Sun Dec 10 2017

.UPDATE...
Issued at 1241 AM EST SUN DEC 10 2017

Forecast still looking good. Snow showers should be exiting the
area in the next couple of hours, giving way to mostly cloudy
skies. The clouds will gradually scatter out through early Sunday
morning. The latest obs were ingested into the forecast grids to
establish new trends.

UPDATE Issued at 1032 PM EST SAT DEC 9 2017

Did another quick update to deal with latest radar and satellite
trends. Another issue tonight will be temperatures in conjunction
with cloud cover. Did make some changes to the temperature curve,
but it is possible the minimum temperatures will need to be
further modified if trends continue.

UPDATE Issued at 911 PM EST SAT DEC 9 2017

A cold front that is likely crossing the region right now is
continuing to lead to light to moderate snow showers for a few
spots this evening. The upstream radars have continued to show
decreasing coverage in snow showers as drier air filters
southward behind the front. Therefore did update the wording on
the SPS to better reflect the trends and continued issues with
black ice and re-freezing potential overnight. Otherwise upper
level trough axis and cold front moves east tonight, and this
will lead to more breaks in the clouds throughout the night. The
grids were updated to reflect latest forecast thinking and latest
obs.

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 06Z TAFS through 06Z Sunday night)
ISSUED AT 1241 AM EST SUN DEC 10 2017

Most of the TAF sites have already improved to VFR as snow showers
continue to exit the area and cloud decks slowly rise. SYM and SJS
were still experiencing MVFR CIGS at TAF issuance, but even these
sites should be VFR by 8 or 9Z. Clouds will gradually scatter out
during the night, with partly cloudy skies expected to prevail
by 13 to 15Z today. Winds will continue to be out of the west
southwest at around 5KT through early Sunday morning, before
increasing to 5 to 10KT by Sunday afternoon.

&&

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

$$

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


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