Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 160541

National Weather Service Jackson KY
1241 AM EST Thu Nov 16 2017

Issued at 1049 PM EST WED NOV 15 2017

Some light returns are noted on radar in the Bluegrass, with
lowering cloud decks and visibilities. Have carried a few hours of
drizzle as a short wave trough moves through the area. The latest
satellite trends reveal clearing across western Kentucky. This
will move into our northwest counties between 06 and 07z at its
current pace, with clearing eventually working in to our far
southeast by around 10z. Have adjusted the sky cover accordingly,
while allowing for a little room for error, as clouds typically
get hung up against the terrain. Temperatures are still running
around 50 degrees for most locations, and this should continue
until the cold front moves through the area. Lows ranging from the
upper 30s in the northwest, to the lower 40s elsewhere, still
look on target. Updates have been sent.

UPDATE Issued at 749 PM EST WED NOV 15 2017

The bulk of the showers have exited off to the east, as dry
slotting works in from the west. The surface cold front remains
well off to our west and northwest, so would expect a temporary
lull in the activity, until it moves through later tonight. Have
allowed for more of a separation between the pre-frontal showers
and light rain/drizzle to occur near or just behind the cold
front. Updates have been sent.


.SHORT TERM...(This evening through Thursday night)
Issued at 340 PM EST WED NOV 15 2017

A cold front is poised to shift southeast across the Ohio River
and across portions of Kentucky late this afternoon, traversing
eastern KY this evening and overnight. WPC shows this front
exiting just SE of the state after 9Z. A line of precip is moving
in ahead of this frontal boundary, in the form of rain. This
precip line is currently making its way into the NW CWA and will
continue to shift eastward across the CWA through the evening and
first part of the overnight. Just behind the frontal passage, dry
air will move in and cut off precip potential. This dry air will
cut off the mid level moisture first, leaving llvl moisture
trapped below a pretty steep inversion. As such, did include some
patchy drizzle in on the backside of the precip as it is tapering
off after 6Z.

For Thursday, deamplified ridging moving across the south central
conus, and a shortwave exiting NE of the Ohio Valley will result in
rising heights across our region. An area of surface high pressure
across the mid and upper Mississippi Valley at 1Z Thursday will
shift eastward across the Ohio Valley and Kentucky Thursday and
Thursday night. This dry westerly flow and rising heights will
promote mostly clear skies but post frontal temperatures that are
some 10 degrees below seasonal normal, in the upper 40s and low 50s.
By thursday night, the location of the high will be passing almost
directly overhead, subduing winds and making for ideal conditions
for net radiational cooling. Ridge valley splits will be likely,
especially in the east. Dropped the far east valleys down around 5
degrees from rest of the CWA, but wouldn`t be surprised if this
spread ends up being even more. Rain tonight could provide enough
lingering moisture to also promote fog, especially in theses cooler
valleys. Did include patchy to areas of fog in the deeper valleys as

.LONG TERM...(Friday through Wednesday)
Issued at 359 PM EST WED NOV 15 2017

A rather progressive pattern is expected to continue into the
long term period with mid and upper level as well as surface
ridging shifting east of the area from Friday into Friday night
while the next trough will begin to approach from the Plains.
Individual shortwaves are expected to consolidate as the system
approaches the MS Valley with the trough starting to become
neutrally if not negatively tilted as it moves across the OH
Valley and Great Lakes and into the northeast from Saturday into
Saturday night. Height rises and shortwave ridging is expected to
work into the area to end the weekend before moving east of the
area later in the period. Model agreement decreases in the
longwave details as with timing of individual shortwaves from
late Monday through the end of the period.

At the surface, high pressure will move east of the area with
temperatures moderating on increasing southerly flow on Friday.
The cold front will move into the area on Saturday afternoon,
moving east of the area on Saturday night. The pressure gradient
and winds aloft will increase with winds near 850 mb reaching near
50kt if not 55kt on Saturday. Winds will likely gust to 30 mph or
more late Friday night on the higher exposed ridges above 2500
feet msl. Some of the momentum should mix down with some mixing
ahead of the front and around or just prior to the arrival of a
band of showers. 12Z GFS BUFKIT momentum transfer suggest
potential for as much as 39KT gusts from JKL over to SJS and on
into far northeast KY, but 12Z NAM remains generally 25kt or less.
Have opted to go in the middle near the 30KT mark for wind gusts
on Saturday and increased sustained winds a bit from Superblend
more toward some of the statistical guidance. The degree of
heating ahead of the front on Saturday and strength of warm
advection will determine how high temperatures will max out ahead
of the showers on Saturday. Some of the statistical guidance
suggests values warmer than the superblend and current forecast
which was a tad warmer than the superblend over the southeast.
This system should bring a bit higher qpf than the current near
term system with a quarter of an inch or so on average with some
locally higher amounts.

Colder 850 mb air will move into the area following this front and
low level moisture possibly deep enough to reach -8C to -10C
could linger late Saturday night or very early on Sunday across
the VA border and far southeast KY. The higher ridges will
probably cool off enough that if that occurs some snow could mix
in with any possibly rain showers. 850 mb temperatures should
bottom out in the -3C to -6C range at least around 12Z Sunday,
with the past 6Z and 12Z GFS and 0Z ECMWF 850 temperatures colder
than that. The bottom line is Sunday will be well below normal by
15 to 20 degree range. The MOS guidance was about 3 degrees warmer
than superblend and opted to go about a degree warmer than the
blended guidance for max T on Sunday and lower max for the highest
terrain as well more in line with what the 850 mb temps support.

Dry weather should prevail for most of Sunday through Tuesday with
moderating temperatures. Uncertainty remains for the middle of
next week, but opted for slight chance pops late Wednesday to
give the latest GFS run some credit. It is certainly possible
that Wednesday could remain dry.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)

Most sites are beginning the TAF cycle with MVFR to IFR CIGs and
even some VIS restrictions for fog/drizzle. The latest GOES-16
imagery is showing a good amount of clearing and drier air moving
into portions of western and central Kentucky. Therefore, will
taper the clouds off from northwest to southeast through the
overnight into the dawn hours. Then we will see sites improve to
VFR across the board to round out the period. Winds will remain
light out of the southwest then veering west to northwest through
the overnight into later today.




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