Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 260248

National Weather Service Jackson KY
1048 PM EDT Sun Sep 25 2016

Issued at 1048 PM EDT SUN SEP 25 2016

The forecast is still on track so far tonight. We will see another
night of warmer than normal temperatures across eastern Kentucky,
with lows in the 60s across the area. Cloud cover will continue to
slowly increase overnight, with partly cloudy skies expected by 10
or 11Z on Monday. Patchy dense valley fog is also expected, so the
forecast is good as is. Ingested the latest into the hourly grids
to establish some new trends, but not other changes to the
forecast were deemed necessary at this time.

UPDATE Issued at 746 PM EDT SUN SEP 25 2016

Forecast still on track so far this evening. Cloud cover will
gradually overspread the area overnight, with 40 to 60 percent sky
coverage expected by 12Z Monday. Patchy valley fog, dense at
times, is also still on tap tonight, with near calm winds and
mostly clear to partly cloudy skies expected. Ingested the latest
obs into the hourly forecast grids to establish new trends. No
other changes to the forecast were needed at this time.


.SHORT TERM...(This evening through Monday night)
Issued at 327 PM EDT SUN SEP 25 2016

An upper level ridge remains in place across the Ohio River Valley
today, but should start to break down overnight as an upper level
wave and associated troughing move eastward into the upper
Mississippi River Valley. The associated wave will strengthen into
an upper level low across the Upper Great Lakes by tomorrow
afternoon, with the deepening axis of the trough swinging across
Kentucky throughout the day tomorrow as well. Models remain in good
agreement through Monday night, with the closed low showing little
forward momentum, but continuing to rotate and gain intensity
throughout the night. This will keep lowering heights across the
Ohio River Valley as well. This low will tap into the northern
stream of the jet stream, with a strong pull of Canadian air
expected to propagate southward and into the Ohio Valley.

At the surface, a low pressure system is currently in place across
southwest Ontario, coinciding with the upper level wave. This too
will continue to push eastward and just north of Lake Superior
overnight. A cold front is extending southward from this low,
presently draped across WI, western Iowa, Missouri, and points to
the southwest. A weak warm front is also extending from the low,
currently draped across KY. This warm front is causing little impact
to the ongoing weather pattern, however, with light winds and the
upper level ridge still in place, abundant sunshine has boosted
temps back into the mid and upper 80s once more this afternoon.
Temperatures will quickly start to cool down this evening and into
the overnight, with the cold front expected to make it into western
KY by around midnight. Winds across eastern KY will begin picking up
in speed slightly as they shift to a more S to SW direction during
the overnight as well. This will begin pulling in some moisture in
the form of clouds into the region, and then eventually
precipitation just after daybreak tomorrow (Monday).

Best precipitation chances will occur along the actual frontal
boundary as it traverses eastern KY during the day tomorrow. Decent
CAPE values according to the latest NAM12 soundings would promote
some thunder potential with this system. While soundings do not
favor hail potential, especially given the warm airmass in place
leading into this event, some gusty winds and frequent lightning
cannot be ruled out. That being said, once the cold front pushes
through a location, winds will quickly shift to the Northeast and
allow much cooler and drier air to begin filtering in. This, in
addition to loss of daytime heating tomorrow evening, should quickly
cut off best thunder potential across the CWA after 0Z. This is
reflected in the quick loss of instability in the forecast soundings
as well. Some rain showers may continue throughout the night in the
far southeast due to upslope flow.

It is during this time Monday night that we really start to tap into
that strong pull of drier and colder Canadian air. This will result
in clearing skies, aiding in the fall of overnight temps. While
overnight lows are expected to be in the mid 60s tonight, overnight
lows on Monday night will likely drop into the mid and upper 40s for
much of the region. This pull of colder and drier air will continue
into the mid and long term portion of the forecast as well as the
upper level features show slow progression from this point

.LONG TERM...(Tuesday through Sunday)
Issued at 327 PM EDT SUN SEP 25 2016

After agreement on a cool and dry start to the period, models
continue showing disparity for the remainder of the period. A cold
front will be well to our southeast on Tuesday, with dry air in
place behind it for the local area. The upper level system which
initially drives the cold front through will then become our main
player. This large upper low will be moving south over the western
Great Lakes Tuesday and Tuesday night, and into the Ohio Valley
Wednesday. Although models do not agree on the evolution of this
system, there are trends observed. The ECMWF is fairly consistent,
but has shown a bit of a drift even further to the west as compared
to 24 hours ago. Meanwhile, the GFS and its ensemble have made the
larger shift, with a move toward the ECMWF solution. Instead of
being progressive with the system, the GFS now also holds back a
significant upper low (although, not as far west as the ECMWF). That
being the case, will take the forecast more toward the ECMWf. This
results in below normal temps and a potential for showers during the
later part of the work week as the large, nearly cut-off upper low
wobbles near KY.

By the weekend, both the ECMWF and GFS have the low weakening
considerably and lifting out to the NE-- albeit with different paths
and timing. There is no return of low level warm air advection yet,
but mid/upper levels warm with the jump in geopotential heights.
This should lead to stabilization and an end to showers, and
decreasing clouds.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)

High pressure will remain in control of our weather through
Monday morning resulting in VFR conditions for most areas with
light and variable winds. Skies will be mostly clear to partly
cloudy for most of the night. Our far eastern counties may see BKN
low level cloud cover 12Z Monday. Patchy valley fog will be
around again towards dawn Monday, possibly affecting LOZ and SME
with some MVFR BR for a couple of hours. A cold front will
approach eastern KY by Monday afternoon. This could bring with it
increasing chances of showers and thunderstorms for the remainder
of the afternoon. Best potential should be after 18Z, so trended
the TAFs towards these changing conditions, with MVFR conditions
possible at SYM and SJS between 18 and 19Z Monday.




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