Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 031445 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
945 AM EST Sat Dec 3 2016

.UPDATE...
Issued at 945 AM EST SAT DEC 3 2016

Updated the forecast to better reflect the current cloud cover
across the area. Based on the latest satellite obs, most of
eastern Kentucky has been under overcast skies for the past few
hours, and it appears this trend will not change anytime soon.
Therefore, the sky cover grids were updated to reflect cloud skies
for most locations for the rest of the day. The updated zones have
already been sent.

UPDATE Issued at 656 AM EST SAT DEC 3 2016

Low stratocu continues to encompass much of eastern KY. This has
allowed for more regulated temperatures through the early morning
hours, and reduced any ridge valley split from earlier in the
evening. Expect temperatures to begin rising over the next hour as
the sun rises. These clouds will likely hold on through much of
the morning, and will finally start breaking apart this afternoon
in the south, eventually making its way to the northern CWA by
late this evening. The remainder of the near-term forecast seems
to be well on track with current conditions. All changes have been
published and sent to NDFD/web.

&&

.SHORT TERM...(Today through Sunday)
Issued at 356 AM EST SAT DEC 3 2016

Surface high pressure will continue to overspread the state
throughout the day today, passing just to our east by 6Z tonight.
Overall this will result in light winds at the surface with llvl
stratus clouds continuing to pull into the region from the NE
through at least mid day in many locations. Llvl winds will begin to
lighten and become more variable as the center of the high passes to
our north and then heads east, allowing the llvl clouds to begin
breaking up throughout the afternoon. Meanwhile, aloft, a shortwave
will begin digging across the northern plains throughout the day,
shifting eastward. This shortwave is expected to reach the
Mississippi River Valley by Sunday, then move across the Ohio River
Valley and points to the north by 0Z Monday.

The upper level wind pattern will feature a jet streak across the
Ohio River Valley ahead of the shortwave, increasing in strength as
the shortwave nears. Mid/upper level winds will be westerly across
KY and then SW just to our east. This will effectively pull moisture
from the Gulf of Mexico northward and then eastward into the state.
As such, this will result in high clouds expected to push northward
into the CWA by later this afternoon. Moisture and clouds will
continue to build this evening with the nearing mid/upper level
wave, however it will have a hard time overcoming the bubble of dry
air at the surface with the surface high pressure center still in
place just to our east. Latest forecast soundings show moisture
finally overcoming the drier air between 6 and 9Z at KSME and KLOZ
in our southern CWA, between 6 and 12Z in the mid sections, and a
few hours later in the northern CWA.

Despite W to SW flow aloft, temperatures in the mid and upper levels
will still be on the cooler side as precip moves into the region
overnight Saturday, below freezing through much of the column. As
such, even as temperatures at the surface may be at or above
freezing at precip onset, rain may still mix with snow for the first
couple of hours. However, temperatures will quickly warm as we head
into the daytime hours, with the surface high continuing eastward
and allowing warmer return flow at the surface.  All precip will
change over to rain during this time, with generally no snow
accumulation or impacts expected. Rain is expected to continue
through the day Sunday as the mid/upper level shortwave closes in on
the region. This will produce generally between 0.10 and 0.20 inches
or rain across the CWA, an overall light system but much needed none
the less.

.LONG TERM...(Sunday night through Friday)
Issued at 503 AM EST SAT DEC 3 2016

Challenging extended package this morning. Models are in
good agreement for DYS 3-4 but diverge significantly beyond that
both with the details of the mid/upper level pattern as well as
with sensible weather. Mid/Upper level cut off low moving out of
Texas Monday opens up into a wave by Tuesday as it transits the
MS/TN/OH valleys. This feature will provide another soaking rain
to the area with models spitting out around an inch of rainfall
on average, mainly from Monday night through Tuesday.

Forecast gets complicated thereafter as a series of disturbances
rotate around a low pressure system residing along the Northern
Tier and southern Canada. Models appear to have difficulty with
the strength and timing of several lobes of energy rounding this
parent low. The GFS presents a quicker solution with weaker
disturbances. The ECMWF advertises stronger disturbances which
dig a bit further south resulting in an overall slower solution
and correspondingly stronger surface features. The Canadian
generally provides partial support for both solutions.

For sensible weather we can expect a seasonably warm start to
the extended but cool significantly through the period after
Tuesday. Rain will be tapering off Sunday night before
redeveloping across the region Monday night into Tuesday. There
is very low confidence with respect to precipitation types and
amounts beyond that. Depending on your model of choice we could
see anything from rain to snow from Wednesday night through
Friday. At this time felt the best approach was to stay close to
the blend of model solutions and guidance which suggest that a
wintry mix of precipitation will be possible through that time
frame depending on the time of day/night.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 708 AM EST SAT DEC 3 2016

Despite incoming surface high pressure, llvl stratocu has settled
across the area throughout the night and will continue through
much of the morning, before finally breaking up from south to
north this afternoon through this evening. This CIG deck is
bordering the line between MVFR/VFR, but given overnight trends,
kept with the MVFR hedge in the TAFs. A mid/upper level
disturbance will begin to approach the region this
afternoon/evening as well bringing with it a strong pull of
moisture from the Gulf of Mexico. So as llvl clouds begin to clear
out, high clouds will begin moving in and thickening to OVC.
Expect high clouds to continue to build down throughout the
remainder of the night, but should stay VFR through the entire TAF
period. As moisture continues to increase with the thickening
clouds, a chance of rain/snow will also move from south to north
across the CWA, generally after 9Z. Used VCSH to cover this as
exact timing at a given TAF site is still somewhat low confidence.
Given that any snow that falls will likely be mixed with rain and
will not accumulate on any surfaces, not expecting much in the way
of additional impacts. Winds will remain generally light and
variable near the surface through the period, with stronger WNW to
W flow aloft. However, the directional change and increase in flow
will be gradual enough to not cause any llvl wind shear problems
throughout the period.

&&

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

$$

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



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