Area Forecast Discussion
Issued by NWS Jackson, KY

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393
FXUS63 KJKL 261859
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
259 PM EDT Wed Jul 26 2017

.UPDATE...
Issued at 105 PM EDT WED JUL 26 2017

Forecast continues on track, and only inconsequential changes were
made in blending obs into the forecast.

UPDATE Issued at 926 AM EDT WED JUL 26 2017

Forecast was mainly on track. Have updated to blend morning obs
into the existing forecast grids, with no substantive changes.

UPDATE Issued at 705 AM EDT WED JUL 26 2017

Did a quick update mainly just to touch up the T and Td grids per
the latest obs and trends. These have been sent to the NDFD and
web servers.

&&

.SHORT TERM...(Today through Thursday)
Issued at 400 AM EDT WED JUL 26 2017

07z sfc analysis shows high pressure in control of the weather
over eastern Kentucky. This has cleared the sky and brought in
drier air. Despite this, patchy dense fog is developing the far
eastern valleys as seen via the GOES16 Nighttime Microphysics
channel. The obs are not very indicative of any fog with just the
KBYL site, along the Cumberland River, reporting lower vis at this
point. The dewpoints have come down from last night and current
vary from the upper 50s north to the mid 60s south as the winds
are light to calm. Temperatures meanwhile, are showing some ridge
to valley distinctions ranging from the upper 50s in the most
sheltered of eastern valleys to the mid 60s south and on the
ridges. Expect a bit of an uptick in the fog towards dawn, but
still mainly confined to the river valleys.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict the Central U.S. ridge
retreating to the southwest by Thursday morning as a series of
identifiable shortwaves slide southeast in the mid level flow and
into the heart of the Ohio Valley. These waves will promote
height falls over eastern Kentucky into Thursday morning ahead of
a larger and stronger wave dropping into the Great Lakes. This
latter wave will bring a favorable wind pattern through the mid
levels capable of supporting organized storm clusters and has the
potential to contribute to severe weather through the region from
Thursday afternoon into the first part of the night. The model
agreement suggests that a blend is the way to go - though a strong
lean toward the higher resolution models like the HRRR and NAM12
is also warranted due to the small scale nature of the features
important to the forecast - especially on Thursday.

Sensible weather will feature another rather nice day, once the
river valley fog burns off, with mostly sunny skies and warm
temperatures, but not as humid as we saw late last week. However,
an increase in clouds and moisture will occur starting in the
evening and continuing through the night. The approach of a sfc
low from the northwest will bring a threat for storms to the area
during the pre-dawn hours Thursday with greater chances seen
later the day as the winds increasingly strengthen and veer with
height through the afternoon along with likely a strong build up
to the instability. Morning convection may limit this instability,
but the other ingredients should be pretty solid for at least
strong storms around the area starting in the afternoon. High PW
air will also support heavy rains, but any individual cells should
be progressive enough to limit excessive rainfall concerns -
barring significant training of storms. Have beefed up the
thunderstorm wording in the HWO for this and will also be sure and
highlight it in the weather story.

The CONSShort was again the basis for all short term forecast
grids with only minor point adjustments made to lows tonight to
impart more of a ridge to valley temperature split. Also fine
tuned the PoPs for the convection potential late tonight and
through the day Thursday.

.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 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 130 PM EDT WED JUL 26 2017

Mainly VFR conditions are expected through the period, with two
exceptions. Valley fog may affect some locations again late
tonight into Thursday morning, but is likely to be more limited to
the deeper valleys. The fog could result in isolated IFR or worse
conditions. Also, a few showers and thunderstorms are possible
from around sunrise through the end of the period, but there is
still uncertainty about their occurrence. The precip could also

&&

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

$$

UPDATE...HAL/GREIF
SHORT TERM...GREIF
LONG TERM...SHALLENBERGER
AVIATION...HAL



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