Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 280246
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1046 PM EDT Tue Sep 27 2016

.UPDATE...
Issued at 1046 PM EDT TUE SEP 27 2016

Temperatures continue to dropoff quickly in valleys underneath
clear skies. Accordingly adjusted overnight lows down another
couple of degrees to account for this, with valleys dipping into
the upper 30s to lower 40s by Wednesday morning.

UPDATE Issued at 759 PM EDT TUE SEP 27 2016

Valley temperatures dropping off very quickly this evening, with
Quicksand and Paintsville both already sitting at 56 degrees.
Valley fog will be in the cards through Wednesday morning given
these cooling temperatures under mostly clear skies through much
of the night.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 405 PM EDT TUE SEP 27 2016

After the passage of a cold front yesterday, surface high pressure
has set in across Kentucky. Meanwhile a strong upper level low
remains in tact across the UP of Michigan, with a troughing in place
across much of the eastern half of the conus. This is resulting in a
strong pull of colder and drier Canadian air from Canada, southeast
and into the Ohio River Valley. This combination of colder and drier
air has resulted in clear conditions across the region through
today, with afternoon temperatures cooling down to more seasonable
normals.

As we head into the overnight this high pressure should continue,
with strong subsidence in place helping temperatures to drop off
into the 40s once again by early morning. While dry air advection
has been in play through the day, still expecting some of the deeper
valleys to see some fog development overnight, especially near
bodies of water. Also throughout the overnight, the upper level low
will begin to make a southward push, reaching the southern extent of
Lake Michigan by 12Z Wednesday.

Heights will continue to lower aloft through the day Wednesday as
the upper level low bowling balls itself southward, reaching central
Indiana by 0Z Thursday. At the surface, a closed surface low will
follow along the same southward path, moving into Kentucky during
the afternoon hours Wednesday. From this low will sprout a secondary
cold front, which is expected to traverse eastern KY tomorrow
afternoon. Winds will become more southerly ahead of the frontal
passage, which will pull some moisture into the region in the form
of clouds ahead of the frontal system. Precipitation will accompany
the frontal passage as well, with best chances moving across eastern
KY late afternoon and into the first part of the overnight. A bit
concerned about the coverage with this system. Overall I think the
models are overdone with the moisture considering the overall upper
flow is still pulling in an abundant amount of dry air aloft.
Superblend gave likely pops, while many of the hi-res CAMs are
showing a more scattered line of convection moving through the
region. Ultimately decided to cap pops at high end chances given
uncertainty, though further updates may deem increasing pops to be
necessary.

There is actually a small bit of instability with this frontal
passage. While not much, it was enough concern to introduce some
isolated thunder into the forecast for Wednesday afternoon/early
evening. This instability should cease during the late evening after
the frontal passage, cutting off any further thunder potential.

Forecast soundings are showing llvl moisture sticking around through
the end of the short term forecast period (the remainder of
Wednesday night). There is enough moisture that light rainfall could
continue through much of the night, so kept isolated to scattered
pops in play. Wouldn`t rule out some drizzle in a few locations as
well. Generally cloudy skies and ongoing precip will keep conditions
insulated a bit more compared to tonight, despite the northerly wind
shift after the cold frontal passage. Lows tomorrow night should
bottom out in the upper 40s and low 50s.

.LONG TERM...(Thursday through Tuesday)
Issued at 450 PM EDT TUE SEP 27 2016

For the pattern being forecast, the models are in good agreement.
A "bowling ball" of large, closed, nearly cut-off upper low will
be situated over KY as the period starts. It will wobble for a
couple days, before slowly heading back north and being absorbed
into the westerlies. While it is here, the cold pool aloft will
lead to instability, with a max during the heating of the day. The
term heating is used loosely, as readings should not get out of
the 60s on Thursday and Friday. Aside from diurnal trends,
specifics for timing and placement of precip will depend on finer
scale details of features rotating around the upper low. Have
continued to use a somewhat broad brush approach due to a lack of
confidence in the handling of these features. Models do show
pockets of strong enough instability to support some thunder
during the afternoon hours on Thursday and Friday.

As the low heads back north over the weekend, dry weather should
return for Sunday through Tuesday. No significant low level warm
air advection is expected through the end of the period, but
additional sunshine and mixing, along with warming temps aloft
will allow for a slow warming trend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 759 PM EDT TUE SEP 27 2016

VFR conditions should remain in play through much of the period.
Clear skies along with light winds through much of the night will
lead to valley fog overnight into Wednesday morning. Have kept any
visibility reductions out of the TAFs as dewpoints were able to
mix into the upper 30s to low 40s this afternoon. Cloud cover will
be on the increase from the northwest late tonight into Wednesday
as an upper level disturbance and associated cold front approach
eastern Kentucky. Additionally, SYM will have a chance at seeing
some nearby showers by late morning/early afternoon. Rain chances
will be slightly less farther south and will also arrive a little
later in the day. Ceilings will begin to develop through the
afternoon, but look to hold in the VFR category through early
Wednesday evening at this time.

&&

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

$$

UPDATE...GUSEMAN
SHORT TERM...JMW
LONG TERM...HAL
AVIATION...GUSEMAN



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