Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 261747

National Weather Service Jackson KY
147 PM EDT Mon Sep 26 2016

Issued at 1254 PM EDT MON SEP 26 2016

Updated the POPs and associated weather over the last couple of
hours to better line up with earlier thinking. The main line of
convection is weakening and starting to break down. Meanwhile,
clouds are quickly developing and convection is starting to pop
across eastern Ky over the last hour in the warm sector ahead of
the front. Expect our northern counties to see coverage pops as
the line continues to make its way eastward, but the rest of the
CWA, especially the Southern portions, could see more scattered
convection. With northwest winds, convection will also be more likely
in the highest terrain along the VA border. That being said, with
low clouds and cooler air moving in ahead of the initial line,
instability is much weaker than originally anticipated. Kept in
some isl to sct thunder, which may still be possible with some of
the pop up activity starting to take place across eastern KY.
However, initial line has weakened to the point that any further
thunder activity may be unlikely.

Also made sure the near term forecasts for temps, dew points, and
winds were on par with current conditions by loading in the latest
observations. All changes have been published and sent to
NDFD/web. A new forecast package was sent out to reflect new
weather wording.

UPDATE Issued at 944 AM EDT MON SEP 26 2016

Continuing to monitor a line of showers and thunderstorms moving
into the western and central portion of the state this morning.
This line remains collocated with the frontal boundary location.
However, of note, winds ahead of this line and ahead of the actual
surface front are already shifting in direction. While much of the
CWA is seeing light SW winds, winds are quickly switching to a
more NE direction just along our western CWA border ahead of the
line of precip. At first glance it was thought that the frontal
boundary may be outrunning the precip, which would bring about the
demise of the initial line but could cause some redevelopment
across our CWA a little earlier than originally forecast. However,
upon second glance it appears as though the frontal placement is
in tact with the precip, but the wind shift could just be the
result of an outflow of the line or perhaps a secondary weak
trough axis.

Either way, this will be something to watch as it will likely
cause a weakening of the initial line as it continues to push
eastward, especially considering low stratus is now outrunning the
initial line as well. That being said, some redevelopment may
occur ahead of the line, across our CWA where warmer temps and
clearer skies still exist, but latest Hi-RES CAM models all
support only scattered convection across our CWA throughout the
day. And interestingly enough, most of them are also lining up
with the thought of the initial line continuing to lose strength
as it pushes eastward as well, showing the line continuing to
shear out through 18Z and scattered convection popping up across
eastern KY during this time. Will continue to monitor as we head
through the next few hours in case any updates to POPs need to be
made, but if this idea holds together, results of this line could
be quite benign with some locations missing out on rain all

A new forecast package was sent out with this update to remove
morning fog wording. The latest observations for temps, dew
points, and winds were also loaded into the near term forecast to
make sure it was well on track with current conditions. All
changes have been published and sent to NDFD/web.

UPDATE Issued at 715 AM EDT MON SEP 26 2016

Another quick update to fine tune temps, dewpoints, and sky cover
through the next few hours based on current obs and trends. These
have been sent to the NDFD and web servers.


.SHORT TERM...(Today through Tuesday)
Issued at 425 AM EDT MON SEP 26 2016

07z sfc analysis shows a well defined cold front moving into the
western portions of the Ohio Valley. However, in the far eastern
parts of Kentucky high pressure remains in control with mostly
clear skies and light winds. As in the past few nights, this has
allowed for a decent ridge to valley temperature difference.
Specifically, readings vary from the low 70s on the ridges to the
low and mid 60s in the more sheltered spots. Dewpoints, meanwhile,
are in the low to mid 60s while the winds remain light. There are
some mid level clouds around, but for the most part skies for
eastern Kentucky are clear while lowering ceilings are approaching
the state from the northwest. The front shows up well on radar,
too. We can see the showers and thunderstorms rolling northeast
along this boundary as they approach western Kentucky. Again in
the east this night, river valley fog has started to form and
some locally dense spots are anticipated through dawn but likely
clearing out quicker this morning than the past few considering
the inbound clouds and winds likely picking up sooner.

The models continue to settle on a similar solution aloft. They
all take the ridge, that has brought extended summer weather to
the area for the better part of a week, east and flatten it out.
The culprit for this pattern change is an impressive early fall
season closed low/trough plowing into the Great Lakes this
morning. This system brings strong height falls, a dynamic wind
field, and ample mid level energy to the Ohio Valley today,
initially brushing by Kentucky to the north. The best dynamics
associated with this will pass by and through the JKL CWA between
18 and 21Z. Following this, heights will continue to fall as the
parent upper low bottoms out, turns over on itself, and starts to
head south down through the Great Lakes. Given the models`
tandem movement to this more extreme solution will favor a
blended starting point with emphasis on the latest NAM and HRRR
for details. Confidence on the specifics is only average at best
given the sense that the models are still in a state of flux
working to resolve this closed low.

Sensible weather will feature any river valley fog burning off
quickly this morning with early sunshine giving way to increasing
and thickening clouds from the northwest. A band of showers and
thunderstorms are expected to enter northwest parts of the area
by late morning, grow in coverage, and sweep through the rest of
eastern Kentucky by late afternoon. Should enough instability
build up ahead of the convective band a few of the storms could
start to organize and become strong with wind gusts the main
threat. Look for the timing of the front to keep the worst of the
storms from developing until they get east of Kentucky, later
this afternoon, but they will still need to be watched closely.
The clouds and pcpn will keep temperatures in check today with
much of the area not likely to get out of the 70s. Much cooler air
arrives tonight in the wake of the front with some 40s anticipated
by morning, especially in the higher terrain and more open areas.
The valleys should hold up a bit better as the cooler air takes a
bit longer to scour them out. Also, anticipate that northwest
winds through the night and the cloud cover will keep fog to a
minimum - for a change. A full fledged fall day will then unfold
on Tuesday with partly sunny skies anticipated and a quite
noticeable change to the air with temperatures only reaching the
low to mid 70s for highs along with much lower humidities.

Started with the CONSShort/ShortBlend for grid population into
the evening and SuperBlend thereafter to 00z Wednesday. Made some
substantial changes to the terrain derived edit areas and
forecast points early this morning and tonight in the temperature
grids to better reflect ridge and valley differences in a neutral
pattern this morning and a cold air advection one tonight. As for
PoPs - ramped them up for later this morning into the likely
category through the afternoon and then dropped them quickly from
west to east after 00z. This is a bit higher than MOS guidance
matching up better with the MAV numbers rather than the MET.

.LONG TERM...(Tuesday night through Sunday)
Issued at 310 AM EDT MON SEP 26 2016

The models have come into better agreement regarding the upper low
currently over the Upper Mississippi Valley. This low will become
closed off and gradually drop southeast towards our area. At the
start of the extended period, the low is progged to be over the
Great Lakes states and then drop southward and be centered over
Kentucky late Thursday. The low will then meander back into the Ohio
Valley region on Friday before weakening and eventually lifting out
of the area over the weekend. Models still struggle with the lows`
exit over the weekend with the GFS taking the low up through New
England while the ECMWF only lifts it into the Great Lakes. Given
these differences, have opted to stay close to the CR Superblend
solution which lifts the showers and thickest cloud cover north of
the area on Sunday.

In terms of sensible weather, it looks like showers and additional
cloud cover will persist from Wednesday afternoon through Saturday
as the upper low remains over the area. With the additional cloud
cover, afternoon highs will be a bit cooler and overnight lows
shouldn`t be as cold as yesterday`s forecast. The coolest days
appear to be Thursday and Friday with highs only in the upper 60s.
Overnight lows will generally remain in the upper 40s and low 50s
through the period.


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

A cold front is currently traversing central Kentucky and will
continue to push across the eastern portion of the state through
this evening. As we went throughout the morning, most of the
precipitation associated with this system was along the actual
frontal boundary. However as we head into the afternoon, a
secondary line has developed across the far eastern portion of the
state (east of all the TAF sites), as the initial line of
convection along the front quickly sheers out to light showers.
For the remainder of the afternoon, expect generally scattered
showers and storms across eastern KY and the TAF sites. Winds will
be from the NW throughout the afternoon, potentially gusting up to
15 knots at times ahead of the frontal passage. Visibilities may
be briefly reduced in some of the heavier showers. CIGs will
remain in the MVFR range across the region until the frontal
passage, which should occur late this afternoon for the
western/northern most TAF sites (KSME and KSYM) and this evening
for the eastern most sites (KSJS). Behind the frontal passage, dry
air will quickly reduce any further chances of precip and CIGS
will improve to VFR, with clouds continuing to lift and clear out
throughout the night. High pressure will move in for tomorrow,
allowing for clear skies and light winds.




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