Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 210557
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1257 AM EST Sat Jan 21 2017

.UPDATE...
Issued at 1257 AM EST SAT JAN 21 2017

All is well with the forecast so far tonight. Middle and high
level cloud cover will continue to stream over the area ahead of
an approaching weather system. Temperatures and winds were still
on track based on the latest obs. The most recent obs were
ingested into the hourly forecast grids to establish new trends.

UPDATE Issued at 655 PM EST FRI JAN 20 2017

Temperatures will fall into the 50s this evening as mid-high
clouds move into eastern Kentucky. Although on a decreasing
trend, low clouds will be tough to shake in a warm sector airmass
characterized by Gulf moisture advecting northeastward.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 401 PM EST FRI JAN 20 2017

A very un-January like warm short term period is in store--
benign to start, but ending with showers and possible
thunderstorms.

Transitory upper level ridging will pass over the area tonight,
while a large longwave trough is positioned over the east Pacific
and western 2/3 of the CONUS. A potent shortwave trough moving
through the large scale system will come onshore on the west
coast tonight, and form a closed low by the time it reaches the
lower Mississippi Valley by Sunday morning. A large and deep surface
low will also develop coincident with the upper low. It will tap
into Gulf of Mexico moisture and a large swath of warm/moist
advection will develop east of the system. Convection is expected
in the deep south and should intercept some of the flow. The
question is to what extent. With such a large and deep synoptic
scale system at all levels, it would seem that there would be at
least enough moisture for showers further north. The ECMWF is the
most restrictive with the northward extent of precip, and the GFS
the most expansive. Both MET and MAV MOS POPs were generally high
end categorical for the JKL forecast area. Have gone between the
MOS POPs and the lower Superblend POPs, using 70% in the
northeast part of the forecast area Saturday night to 80% in the
south. Weak instability is also present, but lapse rate are not
impressive. Have included a slight chance of thunder on Saturday
night.

.LONG TERM...(Sunday through Friday)
Issued at 347 PM EST FRI JAN 20 2017

The extended forecast period begins on Sunday with a continued
active pattern in place across the CONUS. On Sunday, a strong upper
low crosses into the lower MS valley as it travels along the Gulf
Coast before lifting NE into the Appalachians. Current track takes
the heaviest precip along the spine of the Appalachians and into
the headwaters of eastern Kentucky. Models have been pretty
consistent on this track for the past few runs. In fact, as this
feature develops and lifts north, instability will still be
present continuing to support convection, mainly slight chance,
through the day on Sunday. As this feature exits Tuesday morning
and colder air filters in behind it, some of the exiting showers
will change to a rain and snow mix Tuesday morning on top of the
higher elevations but with very little accumulation expected.

Heading into midweek next week, the next wave tracks across the
central Plains and into the Midwest bringing a round of light
showers into eastern Kentucky. Both the GFS and Euro agree with a
drying trend to this feature as QPF amounts will likely be less than
a tenth of rainfall for Wednesday and Wednesday night. However,
following this feature will be a more seasonal airmass filtering
into the area by Thursday and Friday. This will lead to a return of
northwest flow and a period of snow showers possible Thursday
afternoon and Thursday night. Overall, a trend to more normal
temperatures is expected towards the end of next week if not
cooler than normal.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1257 AM EST SAT JAN 21 2017

VFR conditions are expected to prevail during most of the upcoming
TAF period. Middle and high level cloud cover will continue to
overspread the area tonight and most of Saturday, as a weather
system approaches from the southwest. Visibilities should also
remain largely unhindered as winds back south/southeasterly and
the mid and high clouds keep radiational cooling at bay. Winds
look to remain near or below 5 knots as clouds increase and lower
Saturday ahead of the next round of rainfall, likely arriving
later Saturday into Sunday.

&&

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

$$

UPDATE...AR
SHORT TERM...HAL
LONG TERM...SHALLENBERGER
AVIATION...AR



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