Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 270606
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
206 AM EDT Thu Jul 27 2017

.UPDATE...
Issued at 206 AM EDT THU JUL 27 2017

No major changes to the forecast for update purposes. Freshened up
the hourly forecast grids with the available obs data to establish
new trends. Overall the forecast is on track.

UPDATE Issued at 1028 PM EDT WED JUL 26 2017

Moisture gradient presently resides across central Kentucky into
western Kentucky. A few showers and storms have gone up from time
to time along this moisture gradient and expect activity to shift
east into the area by daybreak as the deeper moisture makes
progress to the east. By daybreak, this moisture gradient should
be virtually overhead allowing for some convective development.
Kept this idea going with the rain chances with shower and storm
development expected late tonight into early Thursday morning.

UPDATE Issued at 741 PM EDT WED JUL 26 2017

Models continue to show support for a very juicy airmass settling
into the area overnight into the day Thursday. PWs are expected to
increase to over 2 inches overnight. A weak low level jet is
forecast to develop allowing for some showers and perhaps a
thunderstorm to develop just prior to daybreak. Models seem to
target the bluegrass counties for this early activity, but could
extend a bit to the east towards Morgan and Breathitt counties.
Given the juicy airmass, heavy downpours can be anticipated with
any shower activity late tonight. Steering flow will also remain
fairly weak (generally under 20 knots). This would lead to some
slow moving storms, so have to look for some localized heavy
rainfall in the morning given this environment. Updated
weather/pop grids to reflect a slightly later onset of
shower/storm activity and to increase pops just a bit late tonight
given decent support from the CAMS. Looks like southwest and
southeast Kentucky may stay dry until later on into Thursday.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 400 PM EDT WED JUL 26 2017

Surface high pressure to our northeast is beginning to lose its
grip on our weather as it shifts northeast today. Meanwhile, an
upper trough was gradually starting to deepen over the northeast
CONUS. This is supporting a cold front currently moving southeast
through the Great Lakes and Midwest. Warm air advection ahead of
the cold front will bring a warm front northeast through our area
on Thursday. The combination of increasing moisture, isentropic
lift, and lowering geopotential heights will favor precip Thursday
into Thursday night. The specifics are still uncertain due to a
lack of significant individual features aloft. At times in recent
days, the NAM has shown some potential for severe weather, but the
12Z model runs today were not as impressive. Precipitable water is
expected to be high (~2"+), so heavy rainfall is a concern,
especially if training of cells occurs. As far as timing is
concerned, isolated storms were already ongoing over western KY
and middle TN, and models show some light or spotty precip
showing up in our area by dawn. A 20-30% POP for tonight still
seems to be adequate. Highest POPs will be late Thursday through
Thursday night.

.LONG TERM...(Friday through Wednesday)
Issued at 259 PM EDT WED JUL 26 2017

The extended portion of the forecast begins on Friday with a
typical summer upper level pattern. A stout ridge remains in the
west as another shortwave tracks southeast into the OH Valley. At
the surface, a front that has pushed south will begin to stall
leaving a boundary over eastern Kentucky for the day on Friday.
With the boundary in place sliding slowly to the southeast, some
instability, and ample moisture will be enough for thunderstorm
development over the far southeast along the TN and VA border.
Profiles indicating a dry layer will lead to another day of
concerns for possible strong storms with strong wind gusts. This
is indicated with the SPC outlook as well but organized severe at
this time seems unlikely. The amount of DCAPE with this convection
is somewhat concerning. Highlight of heavy rainfall potential
will likely be with the better lift and moisture swath further to
the east but a few heavy rainers are possible, especially with a
2.02 inch PWAT over the area. Especially with the highly sensitive
basins in the southeast a few minor flooding problems are not out
of the question. The last of the shower activity will exit the
area by Saturday morning.

After an active beginning to the extended, a mid level ridge axis
will shift east over the area. This combined with surface high
pressure directly over the OH Valley will keep the rest of the
extended dry through the middle of next week. Coupled with this,
the lack of return flow and below to average high temperatures
during the extended will keep comfortable weather in place through
the area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 206 AM EDT THU JUL 27 2017

VFR conditions should prevail the remainder of tonight and through
Thursday morning. Showers and storms are expected for first begin
moving into the area around 9Z this morning along and north of
I-64. This trend should continue through out the morning, with
showers and storms gradually increasing in coverage and sinking
further and further south across the area as a cold front
approaches from the north. More widespread showers and storms are
expected after 19Z at all the TAF sites. LOZ and SME should be the
last to see the widespread rain, with numerous showers and storms
not expected at those airports until 2 or 3Z Friday. MVFR
conditions will be possible with any storm or intense showers. The
rain will overspread the entire area this evening and tonight.

&&

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

$$

UPDATE...AR
SHORT TERM...HAL
LONG TERM...SHALLENBERGER
AVIATION...AR



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