Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 201837 AAC

National Weather Service Jackson KY
237 PM EDT Thu Jul 20 2017

Issued at 225 PM EDT THU JUL 20 2017

Hourly grids were freshened up based on recent observations. This
led to no substantial changes. Trends in very isolated convection
in Central KY will be monitored for any possible need for isolated
pops for a few locations. Overall, the ridge and associated warm
temperatures aloft are keeping the cumulus from substantial
vertical development.

UPDATE Issued at 1138 AM EDT THU JUL 20 2017

High pressure at the surface remains in place across the
southeastern Conus while mid and upper level ridging is centered
to the west of KY. Cirrus is currently passing overhead with some
cumulus also having developed in the moist airmass with dewpoints
near 70. The previous forecast was largely on target with only
some slight adjustments made to high temperatures in a few
locations based on Coop highs from yesterday with hourly
temperatures freshened up based on these trends. Most locations at
1500 feet elevation msl and below should again reach 90 or the
lower 90s today while higher elevations climb well into the 80s.
Heat indices in most locations should peak in the upper 90s to 100
range or just above 100. Deeper valley locations as well as
locations in the far north and west should have the highest chance
for heat indices peaking at 100 or just above 100. The SPS has
been freshened up for this wording with the heat also mentioned in
the HWO. Overall, though, no substantial changes were needed at
this time.

UPDATE Issued at 653 AM EDT THU JUL 20 2017

Ended up tweaking lows down a few degrees based on temperature
trends. As sun continues to rise, temperatures will quickly be on
the increase from here on out. Pretty good fog development going
on across eastern KY, especially in the river valleys. This too
should continue to impact the region for the next hour or two
before quickly dissipating with the rising temperatures. Also
tweaked forecast for dew points and winds in the near term to make
sure they were on track with current conditions. All updates have
been updated and sent to NDFD/web.


.SHORT TERM...(Today through Friday)
Issued at 417 AM EDT THU JUL 20 2017

Upper level ridging will continue to build into the region today.
It will dampen somewhat tomorrow in the northern portion of the
state as a strong upper level low over Hudson bay allows for more
WNW to ESE flow across the northern half of the U.S. to shift a
bit southward into the northern Ohio Valley. That being said, even
with this small shift, the upper level ridge will still have
dominant control.

At the surface, high pressure will also be large and in charge
across the state today. The continued building heights will
attribute to yet another day of well above normal temperatures,
reaching 90 or maybe even topping it in most locations. A few fair
weather cu will be possible during the afternoon, but otherwise
conditions should remain dry under this regime. By Friday,
however, a cold front will push towards the region from the north.
Flow will become more S to SW, allowing more moisture to advect in
from the south and boosting humidity levels a bit (though not a
strong surge). This will cause two concerns. First, the presence
of the frontal boundary just to our our north and a warm/more
humid airmass in place, could spark isolated to scattered showers
and thunderstorms during the day, especially in the afternoon.
Best chances will be in the northern CWA and along the high
terrain in the SE. Second, the S/SW flow will boost temps another
degree or two, into the low 90s for highs. This will combine with
the additional humidity in the atmosphere to produce heat indices
just over 100 degrees in most locations. While we are still below
heat advisory criteria based on the forecast, will go ahead and
issue an SPS for heat concerns this day.

.LONG TERM...(Friday night through Wednesday)
Issued at 422 AM EDT THU JUL 20 2017

An upper level ridge will be over the Tennessee Valley, and
surface high pressure over the lower Great Lakes and Appalachians
at the start of the period. The high pressure at the surface and
aloft will be weakening. In the upper levels, this will allow for
slight cooling and a modest increase in wind as a northeast CONUS
trough develops and the westerlies drop further south. At the
surface, increased flow will help to bring Gulf of Mexico moisture
into the area. The combined result will be an overall increase in
shower/thunderstorm coverage as we move through the weekend. A
cold front is expected to approach from the northwest Sunday and
Monday, and this is when the highest POP will be carried. The GFS
and ECMWF agree on the front passing through from northwest to
southeast late Monday and Monday night, allowing for somewhat
cooler and less humid air to move in to finish the period. Until
then, conditions will be uncomfortably hot and humid. The hottest
weather is expected on Friday, before an increase in clouds and
precip starts to hold temperatures down.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)

Surface high pressure and an upper level ridge building into the
area will continue the rather stagnant weather pattern, with VFR
conditions and light winds prevailing through much of the period.
Cu has developed in the 4 to 6kft range but should dissipate
toward 23Z. High clouds will increase somewhat overnight,
especially over the northern half of Kentucky, and stray
convection cannot be completely ruled out during the 6Z to 18Z
period ahead of an approaching cold front for SYM, SJS and
possibly JKL. Patchy valley fog should again affect mainly
non TAF locations in the southern part of the area. Some MVFR vis
will be possible at LOZ and SME between 5Z and 13Z. Winds will
remain light and variable through the period.




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