Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 242028
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
428 PM EDT Mon Jul 24 2017

.SHORT TERM...(This evening through Tuesday night)
Issued at 418 PM EDT MON JUL 24 2017

Coverage of showers/t`storms has increased this afternoon and
warrants a higher POP than was previously carried. Have used high
chance POPs with the broken line dropping south through the
forecast area. This line roughly agrees with what the mesoscale
models suggested, and have extrapolated the precip southeast
across the area and allowed it to dissipate this evening as
models depicted.

The precip was occurring near a cold front dropping south through
the area. It will bring slightly cooler and drier air southward.
However, there`s not a strong influx tonight, and it will be
difficult to scour out all of our surface air mass, especially in
valleys. With drier air arriving aloft, this will set us up for
fog. It seems a safe bet in valleys. Just how far it spreads in
breadth and depth is the bigger question. Suspect it could get
rather dense.

Fog and low clouds will dissipate on Tuesday morning. Following
this, high pressure passing by to our northeast will provide fair
weather through Tuesday night.

.LONG TERM...(Wednesday through Monday)
Issued at 427 PM EDT MON JUL 24 2017

The continued expansive ridge of high pressure will be in control
of Kentucky to start the extended on Wednesday. However, heights
will quickly lower into the day Thursday as upper level low moves
eastward across Canada, and shortwave develops in the troughing
pattern, pushing southward. As this shortwave continues to
strengthen throughout the day and into the overnight Thursday,
will will result in more NW to SE flow across the state, with the
upper level ridge retrograding westward away from the Ohio Valley.
Longwave troughing will continue to amplify across the eastern
U.S. into the weekend, with heights continuing to fall across the
state. Several more shortwaves are expected to follow this SE flow
into the Ohio Valley through the weekend.

At the surface, high pressure will be in control Wednesday and
Thursday. A cold front will push SE into the state starting
Thursday night, spawning from a surface low pressure system
located over eastern Canada, in coordination with the upper level
low. A secondary surface low will also be located along this
frontal boundary, passing through the Ohio Valley and just north
of the state Thursday. The cold front will push southward through
the state Thursday night into Friday, exiting by Friday evening.
Surface high pressure and more northerly flow will then take hold
for the remainder of the weekend.

As for sensible weather, expect dry and continued warm conditions
for the day Wednesday with the surface high and upper level ridge
in control. Temperatures will reach the upper 80s in the afternoon
under mostly clear skies and light winds. Chances for showers and
thunderstorms will expand across the CWA Wednesday night into
Thursday ahead of the approaching cold front, as winds turn more
southerly and a warmer and moister airmass moves into the region.
Likely coverage will be possible across the north in the afternoon
and across the central and south Thursday night as the front nears
closer. Chances will then quickly begin to dissipate from NW to
SE Friday into Friday evening as drier and cooler air moves in
behind the frontal system. The frontal zone will still likely be
in close enough proximity to our SE to spawn isolated to scattered
showers and thunderstorms, mainly across the SE portion of the
CWA, during the day Saturday. However, temperatures will only be
in the low 80s both Friday and Saturday as northerly winds take
hold.

Surface high pressure will continue to build into the region
through the weekend, keeping mostly clear skies in place across
much of eastern KY along with cooler temperatures. That being
said, upslope flow may lead to some isolated convection in the
high terrain in the afternoon. Temperatures will be in the low 80s
still with much lower humidity.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 235 PM EDT MON JUL 24 2017

Isolated showers and t`storms were occurring over the northern
half of the forecast area at the start of the period. Outside of
the heavier precip, conditions were VFR. The precip was occurring
near a cold front. The front and the precip will slowly sink south
through the area this afternoon and evening. Precip coverage
should remain sparse enough so that nothing more than VCSH or VCTS
is warranted in the TAFs. Even though the front will drop to our
south tonight, the influx of drier air will be relatively weak.
This will make it difficult to scour out our humid air, especially
in valleys. The end result will be fog developing in valleys. The
issue is how far it spreads in breadth and depth. The current
forecast takes most of the area to IFR or lower. The places most
likely to avoid it will be on ridges and in the far north. Fog and
low clouds will eventually dry up on Tuesday morning, with VFR
expected by the end of the period.

&&

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

$$

SHORT TERM...HAL
LONG TERM...JMW
AVIATION...HAL


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