Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 261326

National Weather Service Jackson KY
926 AM EDT Wed Jul 26 2017

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...(Thursday night through Tuesday)
Issued at 300 AM EDT WED JUL 26 2017

The extended will start off active and wet, as a cold front moves
slowly across the region. Numerous showers and storms are on tap for
Thursday night and Friday. The rain should steadily taper off during
the day on Friday, especially during the afternoon, as a cold front
moves through. The rain will likely last through Friday night, but
should be out of eastern Kentucky by early Saturday morning. After
that, a ridge of high pressure is forecast to settle over the
region. This ridge should bring dry weather to eastern Kentucky from
Saturday night through the middle of next week.

Temperatures will start off well below normal, due to persistent
cloud cover, widespread precipitation, and cooler air invading
behind a departed front. Highs on Friday and Saturday are forecast
to max out around 80 degrees. Conditions will slowly warm after
that, with daily highs generally in the low to mid 80s from Sunday
onward. After a warm Thursday night to begin the period, lows around
70, nightly lows should be below normal. The weekend may see
temperatures fall into upper 50s and lower 60s as cooler air moves
in. The cooler nighttime temperatures are expected to continue
through the middle of the week, with nightly lows in the lower 60s


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)

VFR conditions will prevail for most sites as mainly valley fog
dissipates early this morning. VFR conditions will return for all
by mid morning with light west/southwest winds of less than 5
knots the rule through the day. For tonight, more clouds should
keep the fog development confined to just the deeper river
valleys. Any convection predawn Thursday will likely be too
fleeting and widely scattered for inclusion in the text TAFS.




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