Area Forecast Discussion
Issued by NWS Jackson, KY

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846
FXUS63 KJKL 230251
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1051 PM EDT Tue Aug 22 2017

.UPDATE...
Issued at 1051 PM EDT TUE AUG 22 2017

Issued an update to the forecast as the Severe Thunderstorm Watch
has been cancelled and mush of the activity has weakened. Adjusted
pops through the night as well with much of the heavier rain
dissipating. In fact will expect instability to wane further with
thunder removed after 06z. Adjusted temps and dew points according
to hourly trends and added some fog to the deeper valleys for
later tonight. A new HWO and ZFP was issued with this update.

UPDATE Issued at 730 PM EDT TUE AUG 22 2017

Main band of strong to severe thunderstorms are sliding southeast
through the area ATTM. The severe threat appears to be diminishing
as the storms are moving into areas previous worked over with late
afternoon storms. The remaining storms are just ahead of a cold
front that will bring a change in air mass to the CWA by dawn.
Look for the storms to gradually exit eastern Kentucky toward
midnight, or shortly thereafter with a few lingering showers or an
odd thunderstorm possible through 06z. As the new air moves in
the pcpn threat will end from northwest to southeast. At this
point it looks like the transition will be accompanied by some low
stratus most places pre-dawn rather than fog, but will have to
watch for that potential if the skies do manage to clear before
sunrise Wednesday. Have updated the forecast to fine tune the PoPs
and Sky cover well into the night with some tweaks to T and Td
per the latest obs and trends. These have been sent to the NDFD
and web servers. A new set of zones and HWO will follow as we
clear the watch box behind the front before too long.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 340 PM EDT TUE AUG 22 2017

A cold front is presently pushing towards the Ohio river with some
showers and thunderstorms developing just ahead of this feature.
Other convection which fired along an outflow from overnight
convection is now pushing its way across eastern Kentucky. Better
bulk shear values remain across central/northern Kentucky, and as
such, activity is really weakening as it outruns the better shear.
After the present showers/storms push on through, will be a few
hours before the next round with the front pushes on through.
With lots of instability still present in central Kentucky,
hesitant to let go of the severe thunderstorm watch yet. Thus,
will hang on the watch for at least another hour or two to see how
upstream convection behaves. Damaging winds will continue to be
the main threat with the strongest storms. All of this activity
and associated front will drop south and east overnight and be on
the way out towards daybreak Wednesday. This will lead to a drier
Wednesday along with much cooler conditions. Some cloud cover may
hang on well into the afternoon before clearing late in the day.
The clear skies will allow a cool night to set up for Wednesday
night as temperatures fall back into the 50s.

.LONG TERM...(Thursday through Tuesday)
Issued at 450 PM EDT TUE AUG 22 2017

The models are in fairly good agreement aloft with the general
pattern through the extended, though there are some significant
difference with some of the smaller scale features. The core of
the main trough residing over the eastern half of the continent
will swing into the Ohio Valley on Thursday. The ECMWF actually
closes off this part of the trough as it crosses northern Michigan
while the other models are a tad weaker and more open with this
feature. The trough bottoms out Thursday night with lower heights
pushing south through Kentucky. The main trough will pull out this
weekend with heights rebounding locally in its wake. As it does
so, more energy packets will start to move across the area from
the west with a hint of weak northwest flow established by Sunday.
At this point, additional energy pours into the Upper Midwest
with the next trough developing to our northwest. In this low flow
environment at mid levels more energy will seep into Kentucky.
Additionally, we will have to watch the upper level core of
`Harvey` and how it eventually progresses onshore and creeps
northeast into the Lower Mississippi Valley on Tuesday - more
consolidated, but further south in the ECMWF and GFS than the CMC.
The remnants of this tropical system could increasingly be a
factor in the forecast for our area into the start of next week -
but that also adds in an amount of uncertainty for the latter part
of the forecast. Given the good agreement on the broad scale
initially and increasing uncertainty/lower confidence later the
blended solution looks like a reasonable starting point with minor
adjustments.

Sensible weather will feature very nice mid to late summer
weather for the bulk of the week as cool Canadian high pressure
settles into the region. This will make for dry and quiet weather
with temperatures below normal through the period. Each night will
likely see a moderate to large ridge to valley temperature split
as the boundary layer decouples. Patchy valley fog can be expected
to develop late at night and run through a couple of hours past
dawn. Return moisture does come back into the picture by Sunday
with diurnally driven air mass showers and through this evening
and thunderstorms possible. Monday and Tuesday`s weather is quite
questionable, though, as the remains of Harvey start to ooze this
way as well as low pressure inbound from the northwest along with
some mid level energy. As such, have brought better chances for
showers and storms into the forecast though with low confidence in
timing and amounts due to the tropical x-factor.

Made mainly terrain based adjustments to the lows each night from
the SuperBlend to account for an anticipated moderate to large
ridge/valley temperature split. Also, adjusted the PoPs to better
minimize any pcpn chances through the weekend and to be less
specific with the threat Monday and Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 800 PM EDT TUE AUG 22 2017

A cold front is swinging south across eastern Kentucky tonight
with a period of showers and thunderstorms. The convection will
bring reductions in visibility and ceilings through midnight. As
the front passes later tonight, some lower cigs could develop late
bringing ceilings back into the MVFR category and possibly even
IFR late. Look for the low clouds to dissipate by midday on
Wednesday. VFR conditions then follow for quite some time. Winds
will be light and variable through the period, outside of any
storms this evening.

&&

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

$$

UPDATE...SHALLENBERGER
SHORT TERM...KAS
LONG TERM...GREIF
AVIATION...GREIF



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