Area Forecast Discussion
Issued by NWS Jackson, KY

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163
FXUS63 KJKL 221158
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
658 AM EST Wed Feb 22 2017

.UPDATE...
Issued at 658 AM EST WED FEB 22 2017

Band of rain showers making slow progress to the south and east
this morning. Still expecting the best coverage through the
morning to be in southeast Kentucky as this shield of rain
converges with showers streaming up from the south.

&&

.SHORT TERM...(Today through Thursday)
Issued at 415 AM EST WED FEB 22 2017

Rain showers continue to drift east across eastern Kentucky this
morning, owing to a multitude of upper level features. Northern
stream energy is highlighted by an upper low across the Arctic, with
trailing cyclonic flow through Canada into the western and northern
U.S. A 300 mb jet streak, associated with a weakening upper low off
the western shore of Hudson Bay, will push east/southeast this
morning allowing for ascending motion in its right-entrance region.
Lift will be further aided by remnant energy extending into the Ohio
Valley, while a southern stream upper low digs into the northern
Gulf of Mexico. Gulf moisture streaming north of this latter
feature, along with diffluence aloft, will keep plenty of low
clouds and rain showers in the offing through this morning and
into a portion of this afternoon. Southeastern Kentucky will see
the greatest rain chances from daybreak on due to being in closer
proximity to the greatest northward streaming moisture and
remaining forcing for ascent. This activity will be slow to push
east as steering flow weakens with time, but drying should
gradually take place this afternoon. Abundant moisture will allow
low clouds to linger despite southeasterly downslope winds at the
surface. Given this, cooler high temperatures will be in store
today with readings generally in the low-mid 60s, with perhaps a
few upper 60s in the Lake Cumberland region where clearing ensues
earlier this afternoon.

A dry period looks to be in place this evening and at least through
early tonight, before a shortwave trough and attendant surface low
traverse the Great Lakes later tonight. Height falls from this,
combined with a developing warm front ahead of a surface low
developing out of the lee of the Rockies in the central Great
Plains, may spark isolated to scattered showers tonight and Thursday
morning. Warm air advection and increasing instability will promote
thunder chances by Thursday afternoon as southwest flow increases
downstream of an upper trough spanning much of the western U.S.
Shower/storm coverage looks to only warrant isolated/scattered
mention at this time given the lack of a nearby surface boundary,
but subtle impulses aloft along with an entrenched warm sector
airmass will be enough to spark a few showers/storms as temperatures
warm into the upper 60s to low 70s.

.LONG TERM...(Thursday night through Tuesday)
Issued at 415 AM EST WED FEB 22 2017

The period will be met with anomalously warm airmass hanging in,
but a near normal airmass will soon be the story for the weekend.
This as a longwave trough moves east and becomes cutoff across the
Northern Plains by early Friday morning. A surface low that
undergoes lee cyclogenesis will deepen, as upper low continues to
take take on a negative tilt. Now this setup could lead to a
double barrel surface low across the Great Lakes, but models are
still trying to resolve the closed versus open upper low. Overall
the models are in decent agreement with bringing a trailing cold
front across the Bluegrass state. A line of Showers and
thunderstorms will develop along and ahead of this boundary and
some of the storms could be strong to severe. However less likely
as you move toward the eastern side of the state. The biggest
issue will be time of day with line of storms not making it into
the region till around 03 to 06Z or later. The model soundings
suggest the instability becomes more elevated and the low level
inversion will be setup making it more difficult to mix down
stronger winds aloft. However given the low CAPE and high shear
environment the SHERBE does show values approaching 1 which is
marginal and best values are further west along the western CWA
border. Even with some of the negatives think a marginal risk for
severe weather across the CWA is reasonable and the primary threat
would be strong to severe wind gusts. The freezing levels are too
high for such a low CAPE environment and would tend to lean away
from any hail chances. These thoughts are also reasonably
supported by some of the analog guidance such as CIPS and SPC
MARS.

Behind the front temperatures will crash and we will head toward
normal temperatures for this time of year. The depth of the upper
level trough will also lead to some complications with GFS
rendering some wrap around moisture and ECMWF indicating more
influence by eastward building surface high pressure. Given the
low QPF and low support from other guidance leaned toward the dry
model blend at this point. This high pressure quickly progresses
east and the upper level pattern becomes a bit more flat in
nature. We then see some weaker perturbations and PVA track
through the flow leading to some smaller chances of precipitation
by Monday. There are differences in the upper level patterns and
this will consequently lead to divergence in the surface features.
Right now best chances hold off till late in the period toward the
Monday night to Tuesday time frame. There will likely be changes
in the overall timing and evolution of this next synoptic system
in subsequent guidance iterations.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
ISSUED AT 658 AM EST WED FEB 22 2017

Ceilings have held in the VFR range through the night and early
morning, except for a brief degrade to MVFR at SYM. Flow
remaining out of the southeast, producing subsequent downsloping
for eastern Kentucky, has proven hostile to low cloud development
thus far. With rain continuing and further top-down saturation
occurring, may still see some MVFR ceilings at all sites for a
period this morning before VFR criteria prevail into this
afternoon as rain comes to an end. A slim chance of showers may
again develop later tonight, but not enough confidence in this to
include mention at any terminal. Not expecting any sub-VFR
ceilings tonight at this time given how conditions have played out
overnight and this morning, but will have to monitor any
developing showers and how much winds veer regarding potential
MVFR possibilities.

&&

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

$$

UPDATE...GUSEMAN
SHORT TERM...GUSEMAN
LONG TERM...DJ
AVIATION...GUSEMAN



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