Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 272117

National Weather Service Jackson KY
417 PM EST Mon Feb 27 2017

.SHORT TERM...(This evening through Tuesday night)
Issued at 417 PM EST MON FEB 27 2017

Showers have exited eastern Kentucky this afternoon as a surface
trough slides across the Appalachians. Abundant cloud cover has
only allowed temperatures to warm into the low-mid 50s, although a
few late day breaks may still allow a few locales to warm into the
upper 50s. May see a minor ridge/valley temperature split
materialize this evening as 20-25 degree dewpoint depressions
remain in place. Have seen these dwindle over the past couple of
hours as passage of the aforementioned surface trough has allowed
winds to veer more south to slightly southwesterly, negating the
downslope effect.

Warm air/moist advection will materialize later this evening and
tonight as a surface low ejects out of the central Plains into the
Midwest, subsequently lifting a warm front through the Tennessee
Valley and eastern Kentucky Tuesday morning. This will take place
downstream of an upper level trough moving across the
Intermountain West, increasing 0-6 km shear to on the order of 50
knots. Following early morning showers moving in across the
Bluegrass and Lake Cumberland regions, showers and thunderstorms
will increase across the remainder of eastern Kentucky throughout
the late morning and afternoon. Instability does look marginal as
temperatures warm into the mid 60s to near 70, with surface-based
CAPE values perhaps approaching 500 J/kg as a stubborn elevated
mixed layer remains in place, stemming from earlier day warm air
advection aloft. Regardless, enough low level veering, leading to
0-1 km storm-relative helicity values of 250-400 m2/s2 as winds
remain backed near the warm front, will exist for updrafts to
remain discrete, given they can grow tall enough to become
organized throughout a significant depth in a highly sheared
environment. Although any stronger storms are expected to be
isolated in nature, gusty southwest winds will become moreso
underneath any storms that develop. Isolated tornadoes can also
not be ruled out given rotating updrafts and sufficiently low LCLs
as PWATS of near 1.2 inches advect in.

Winds aloft will increase further Tuesday night as the upper
trough draws nearer. While an overall lull in shower/thunderstorm
activity is expected late Tuesday afternoon/evening, gusty winds
will continue through the night. Higher ridges may gust to upwards
of 35 mph or greater as deep layer shear further intensifies.
Shower and thunderstorm chances will increase later in the night
toward dawn Wednesday ahead of the approaching cold front, but
more widespread storms should hold off until after sunup. Any
storms that do develop will have the potential to produce severe
wind gusts as higher momentum air aloft will not have far to mix
down. Additionally, some drying aloft may lead to an increased
threat for hail through the night. Will also have to monitor the
potential for isolated flooding given the degree of moisture in
place, but the overall progressive nature of this system should
keep widespread flooding a low risk.

.LONG TERM...(Wednesday through Monday)
Issued at 309 PM EST MON FEB 27 2017

The primary forecast issue in the extended period will be the
potential for strong to severe thunderstorms on Wednesday. A
fairly well defined cold front is forecast to move across the area
on Wednesday, which will bring widespread showers and some
thunderstorms to eastern Kentucky. The best potential for strong
to severe thunderstorms will likely be between 18 and 23Z on
Wednesday, when the model data is suggesting the best instability
will combine with the lift along the front the strong low and
midlevel wind shear. The primary threat with the strongest storms
will be damaging wind gusts. The rain should taper off quickly as
the front moves east of the area early Wednesday night, with the
last rain forecast to exit the area by 6Z. We should see a brief
break from the precipitation Wednesday night and Thursday, as a
ridge of high pressure sets up just to our south. The models are
still suggesting that weak area of low pressure aloft will move
across the Ohio Valley region Thursday night into Friday morning.
The temperatures during that time would allow for rain and snow
showers to occur, should the model data be correct. Since the
models have been forecasting the passing upper low toward the end
of the week fairly consistently, decided to keep precipitation in
the forecast for the northern half of the forecast area for
Thursday night into early Friday. The system will be starved for
moisture, so only slight chance to chances PoPs were used once
again. Any snow accumulation that would occur would likely be
confined to our far northwestern counties, and would be a tenth of
an inch or less on grassy areas.

Once this fast moving systems moves past us, the weather should be
dry Friday through Sunday. A bit better developed weather system
is being forecast to affect the area Sunday night into Monday.
However, the models are not in the best agreement to end the
period, so only slight chance to chances PoPs were used in the
forecast for Sunday night into Monday morning. The blended model
PoPs seemed way overdone, so the lower PoPs were used to account
for the model uncertainty.

Temperatures during the period will be above normal yet again,
with daily highs varying from the 40s to the 60s across the area.
Nightly lows will be cold during the first half of the period,
with minimum values in the 20s and 30s expected. Low temperatures
Saturday night are forecast to fall into the upper 30s and lower
40s, with minimum values expected to only fall into the mid to
upper 40s Sunday night.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)

Rain showers have moved north of SYM, with VFR conditions
expected across the majority of eastern Kentucky into early
Tuesday morning as southeast winds of 5-10 knots prevail. Rain
showers will begin to approach from the southwest early Tuesday
morning as ceilings lower toward MVFR criteria. Additionally,
increasing southwest flow will likely lead to a period of low
level wind shear of near 35 knots at FL020 near and after 12Z
Tuesday. This currently looks to be confined to LOZ/SME, but will
have to monitor for this potentially shifting east. LOZ/SME will
also stand the best chance of hearing thunder within the vicinity
of each terminal prior to 18Z, so have included this along with
veering southerly winds gusting to near 15 knots by mid Tuesday




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