Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 051213
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
713 AM EST Mon Dec 5 2016

.UPDATE...
Issued at 704 AM EST MON DEC 5 2016

Overall forecast seems to be in pretty good shape. Low clouds
continue to linger across the region Did adjust the temperature
curve a bit through this morning as temperatures did not drop
quite as low as originally forecast through the overnight. This
included loading in the latest observations for temps, as well as
the dew points, and winds. All changes have been published and
sent to NDFD/web. No updates to the forecast package will be
needed at this time.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 403 AM EST MON DEC 5 2016

As the mid/upper level wave that impacted the area yesterday
continues to shift northeast of the region, more zonal flow is
taking hold with surface high pressure moving eastward across the
state. That being said, MVFR clouds continue to plague much of the
region under a pretty steep inversion that has set up. Dry air will
continue to filter in aloft and in the mid levels throughout the
day, eventually working its way down to the surface and allowing the
low cloud deck to mix out, generally after 15 to 18Z.

Attention then turns to a strong upper level low positioned over
southern TX this afternoon. At the surface, the center of low
pressure will be located just off the TX/Louisiana coast, but will
continue to push northeastward throughout the day following the
upper level low, quickly reaching Mississippi by this evening, and
TN late tonight, before traversing eastern KY and eastern TN during
the day tomorrow. This will push the center of high pressure
currently across the state to our northeast, and allow deeper
moisture to quickly begin filling into the state from the south,
reaching our southern CWA between 21Z and 0Z this afternoon/evening.
That being said, upper level winds will continue to pull moisture
into the region well ahead of this system, so even as the low clouds
begin to mix out today, high clouds will already begin building in
ahead of this system. Overall, it is not likely that we will see
much of a break in the clouds throughout the day as a result.

According to the latest forecast soundings from the NAM12, the
transition from high clouds to moisture build down and precip will
be very quick. Only slight chance pops are in the forecast along the
TN border before 0Z, but widespread rain is expected to encompass
the entire southern half of the CWA by 6Z, and and the entire
eastern portion of the state by 12Z. A steady rain is expected to
continue throughout the day Tuesday. Still not seeing enough support
for instability, even aloft, to include thunder at this time.

The upper level low is expected to decrease in strength, becoming an
open wave by the time it moves over eastern KY. As the surface low
pressure center moves across the CWA in the afternoon, drier air
will be quick to filter in behind, weakening the surface low and
cutting off best rain potential. As such, rain is likely to end just
as quickly as it started, with only low end chances expected across
far eastern KY by 0Z Tuesday.

While temperatures today will be near seasonable normals despite
cloud cover, the surge of warmer moist air into the region will
actually boost temps well into the 50s for the day tomorrow.

.LONG TERM...(Tuesday night through Sunday)
Issued at 510 AM EST MON DEC 5 2016

Models are finally showing better agreement with mid/upper level
features through the extended and have even seen some trends
towards better agreement in sensible weather elements. A broad
trough moving through the Intermountain west at the start of the
period will reach the Ohio Valley Wednesday night, passing
through during the day Thursday. The 0Z GFS and Canadian, having
been the more consistent runs, are a bit stronger with the mid
level features of this system than the 0Z ECMWF. Regardless the
boundary layer and sfc features associated with this disturbance
are quite weak. Timing is similar with all solutions now, with the
ECMWF only slightly slower. Overall trends are for lower pops and
less QPF potentials. However, this system will still usher in some
very cold air into the region, with H850 temperatures bottoming
out close to -15C. The high pressure system building in behind
this disturbance will settle down directly over the Commonwealth
Friday night, allowing temperatures to drop into the low to mid
teens by Saturday morning. Would not be surprised if morning lows
flirted with some single digits Saturday in our typically colder
valley spots.

Thereafter return flow develops rather quickly, pulling plenty of
moisture northward back through the MS valley and into the OH.
If initial indications are correct, fairly strong isentropic lift
will bring overspreading precipitation back into our area as early
as Sunday. Too early to capture details at this time, but with the
cold air in place imagine that precipitation will probably fall as
a wintry mixture at the onset early Sunday morning before
transitioning to just rain through the day.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 713 AM EST MON DEC 5 2016

Upper level wave is continuing to exit northeast of the region,
with surface high pressure moving in across the state. A strong
near surface inversion is in place, trapping llvl moisture in the
form of MVFR and lower clouds across the region. These low clouds
will likely persist into the afternoon, before finally starting
to scour out generally around 18Z. About this time, another
system will begin approaching from the southwest. The influx of
mid and upper level moisture ahead of this system will allow for
high clouds to filter into the region, and quickly build down
after 0Z, with rain chances soon to follow. Despite being late in
the period, tried to time out the best timing for rain onset as
well as CIG build down to MVFR and eventually IFR. Rain will be
persistent enough to likely cause some visiblity restrictions as
well. KLOZ and KSME will be the first to see the CIG build down
and rain this eveing/overnight given their southern location,
while KSYM will be the last to see impacts close to the end of the
forecast period. Overall winds should be light and variable,
under 10 knots, throughout the day today.

&&

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

$$

UPDATE...JMW
SHORT TERM...JMW
LONG TERM...RAY
AVIATION...JMW


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