Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 251739
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
139 PM EDT Mon Sep 25 2017

.UPDATE...
Issued at 139 PM EDT MON SEP 25 2017

Continuing to see cirrus stream in from the south and southeast
due to Hurricane Maria and a low off the Gulf coast. Still
expecting temperatures to continue warming into the mid-upper 80s
as drier air mixes toward the surface.

UPDATE Issued at 704 AM EDT MON SEP 25 2017

Fog has been showing up well on the fog channel in the Cumberland
Valley over the last several hours. High clouds are currently
moving north and east across eastern Kentucky, blocking our view
elsewhere across the CWA. But from what peaks there are in the
clouds, it appears as though fog elsewhere is limited. Portions
of the Kentucky River basin may be experiencing some areas of fog
with patches of dense fog, though NWS employees have not reported
any problems on their commute in. Will keep fog forecast as is
based on this.

A bit of concern about the thickness of the cirrus moving across
the state. Southerly flow is tapping into moisture coming off
Hurricane Maria, with an expansive area of high clouds across
portions of the mid-Atlantic. This may lead to thicker cloud cover
than originally expected, so sky cover may need to be increased as
we head into the day and see how things pan out this morning.

Made sure the near term forecast was on track with current
conditions by loading in the latest observations. All changes have
been published and sent to NDFD/web.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 407 AM EDT MON SEP 25 2017

A large area of high pressure remains parked just to our NE and
will continue to stay in place through the short term portion of
the forecast. Southerly flow aloft will allow for some wisps of
high cirrus to move across the region again today, but should have
little impact on the surface conditions. A few diurnal CU will
also be possible during the afternoon both today and Tuesday
(better chances Tuesday according to the latest NAM12 soundings),
dissipating in the evening. Did opt to go below guidance a couple
degrees on dew points during the afternoon both today and
tomorrow, based on the fact observations were somewhat lower than
model guidance yesterday. This was coordinated with several
surrounding offices, and will result in forecasted min RH values
in upper 30 to low 40 percent range across portions of eastern KY
this afternoon.

Fog is visible in the deeper valleys again this morning, but is
much less widespread/prominent than last night and is more
concentrated across the Cumberland Valley. Observations in the
Cumberland region are indicating dense fog, so included dense
wording along the Cumberland river through daybreak today. Given
very little change in the overall mesoscale and synoptic set up,
expect conditions to be conducive to valley fog once again
tonight as well. Did not include dense wording at this time as
drier air today might help mitigate some of the fog development.
However, can`t rule out some isolated dense, just not sure at this
point as to where this will be.

.LONG TERM...(Tuesday night through Sunday)
Issued at 433 AM EDT MON SEP 25 2017

The period will begin with Hurricane Maria off the North Carolina
coast and a ridge extending from the Northern Gulf of Mexico in
to the OH and TN Valley Region including East KY. Further west,
downstream of a ridge just west of a U.S. Pacific coast, the
northern potion of a trough over portions of the West and Rockies
into the Northern Plains will have sheared east as an open wave
to near the Ontario/Manitoba border south into the Northern Plains
and upper MS Valley while the southern portion will be starting
to close off over the Desert Southwest. The wave is expected to
translates through Ontario and lead to a breaking down ridging
across the Southeastern CONUS. Meanwhile, the shortwave moving
across Ontario and into Eastern Canada and the Northeast U.S. and
another shortwave moving across the ridging near the west coast
and into Central Canada and the Northern Plains/Great Lakes should
steer Hurricane Maria east rather quickly into the Atlantic
Thursday into Friday after the storm nears the Outer Banks at
midweek.

At the surface, high pressure will remain dominant to start the
period on Tuesday night. However, a surface low pressure system
associated with the first shortwave will track well of the area
across the Northern Great Lakes and into Ontario and Quebec and
eventually the Canadian Maritimes from Tuesday night through
early on Tuesday. The increasingly sheared trailing cold front
will be rather moisture starved and weak forcing along it and
timing of fropa Wednesday evening into Wednesday night should be
unfavorable for shower development. An airmass more typical of
late September will move in behind it.

The second shortwave should work across Ontario and the Great
Lakes and into the Northeast and Quebec Thursday night through
Saturday. Another even more moisture starved boundary lacking any
return flow should move across the area late Friday into Friday
night. A rather strong surface high should build east into the
region behind it for the weekend preceding the axis of mid level
riding that moves from the Plains and into the Eastern Conus over
the weekend. As the rather strong surface high for early fall
builds in, an even colder and drier airmass will be ushered in for
next weekend.

This airmass will be more typical of Fall with temperatures
averaging 5 to 10 degrees below normal. Lows should reach the 40s
in some locations on Saturday morning and in most valley locations
on Sunday morning. These locations should at least reach the mid
40s and COOP MOS guidance suggests a few lower 40s are possible
for Sunday morning in the typically cold spots. The recent model
run is slightly weaker with the surface pressure for the high this
weekend, so confidence in going down to the low 40s for cold
spots on Sunday morning was not high enough to go that low just
yet. Temperatures on Saturday should mainly top out into the upper
60s before rebounding a few degrees Sunday into the low 70s on
average.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 139 PM EDT MON SEP 25 2017

VFR conditions look to largely continue at all sites through the
period. The exception may be later tonight into early Tuesday
morning as valley fog develops and brings local MVFR or worse
visibilities. Have elected to keep mention out of all TAF sites
for now as drier air has mixed to the surface early this
afternoon.

&&

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

$$

UPDATE...GUSEMAN
SHORT TERM...JMW
LONG TERM...JP
AVIATION...GUSEMAN



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