Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 231144 AAB
AFDJKL

Area Forecast Discussion...UPDATED
National Weather Service Jackson KY
744 AM EDT TUE AUG 23 2016

.UPDATE...
Issued at 535 AM EDT TUE AUG 23 2016

Fog, locally dense in spots, has become more widespread across
the southern and eastern counties over the past couple of hours.
Expect this to continue through dawn as temperatures near their
crossover values. In terms of the forecast, increased the fog in
the grids to reflect current trends and freshened up the hourly
temps. Sent updates to NDFD and web servers.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EDT TUE AUG 23 2016

Mid level dry air continues to push southward into Eastern
Kentucky this morning, per latest WV imagery. This dry air has
prevented fog development across the northern counties early this
morning, with some dense fog present in the southern counties
mainly near bodies of water. There is still potential more fog
could develop close to dawn as temperatures near the cross-over
temperatures. However, it won`t be nearly as widespread as the
previous day. Any fog should being to lift around dawn and
dissipate by 13Z.

Surface high pressure will gradually slide off to the east later
today but not before we have another beautiful summer day with
lower humidities. As the high departs, southerly flow will set up
and begin ushering in warmer and more humid air. This additional
moisture will allow for some fog development tonight, mainly in
the valleys and near bodies of water. A weak upper level shortwave
will then cross through the forecast area Wednesday afternoon and
interact with the unstable airmass. This interaction should be
enough to spark isolated showers or thunderstorms during the
afternoon and evening hours, even with mid and upper level ridging
holding steady over the southeastern CONUS. The shortwave, and any
shower activity, should exit the region by Wednesday night.

.LONG TERM...(Wednesday night through Monday)
Issued at 349 AM EDT TUE AUG 23 2016

The long term period is expected to begin with an upper level ridge
of high pressure centered over the Southeastern States while a
somewhat broad trough is expected to extend south through portions
of the Rockies and Plains States from an upper low moving east near
the US/Canadian border centered over southern Manitoba. Surface high
pressure that has brought a reprieve from the humidity is expected be
departing the Northeast at that point. Return flow between this high
and a cold front advancing toward the Great Lakes and MS Valley
ushering deeper moisture back into the Commonwealth. PW is projected
to have increased into at least the 1.5 to 1.75 inch range by the
start of the period. In addition, a few disturbances should
also be moving around the ridge at that point.

From Wednesday night into Friday, the upper low is expected to move
into and across Ontario and Quebec and weaken to an open wave and
approach the Canadian Maritimes by Friday evening. Meanwhile the
associated surface low will also move east from Ontario and toward
the Maritimes during the period. However, the ridging across the
Southeast is expected to build north and east and be centered over
the Central or Southern Appalachians by Friday evening. This will
lead to the cold front becoming increasingly sheared with time and
probably more diffuse as well as it drops south of the Ohio
River. It should usher in a minimally drier airmass for the start
of the weekend. During the period of increasing moisture from
Wednesday night into Friday followed by the approach of the cold
front convection will be possible. However, mid and upper level
forcing should be minimal if not lacking much of the time. Thus
only isolated to scattered pops continue to be forecast during the
Wednesday night to Thursday period. Although nocturnal convection
will be possible on Wednesday night as a weak disturbance passes,
loss of daytime heating should lead to a dry or mostly dry period
on Thursday night. Even with the front progged to move across the
area on Friday the proximity of the center of the upper level
ridge and or height rises should keep coverage mainly isolated.
Upper 80s should be common for highs during this period with some
of the warmer spots or more southern valley locations reaching or
exceeding 90. Overnight lows will return to the upper 60s to lower
70s.

Surface and upper level ridging should remain dominant over the
weekend and into the start of next week. There remains uncertainty
as to how close the center of the ridge will be to Eastern KY during
this period. The past couple of ECMWF runs have higher heights from
Friday evening into Saturday night, while the GFS and the previous
ECMWF run have higher heights at the end of the period compared to
the 0Z ECMWF run. The airmass should be moist enough for at least
diurnally driven cumulus each day, with some of this possibly able
to break the cap in a few locations each day. This would appear
most likely over or near the higher terrain near the VA border to
start the period. Then as the ridge possibly weakens or becomes
centered further from the area, the cap possibly could be broken
across more of the area on Monday. A warm and moist airmass will
be across the region in any case with dewpoints expected to be in
the upper 60s to lower 70s and 850 mb temps around 19C to 20C
should keep temperatures in the upper 80s to around 90 for highs
with overnight lows in the upper 60s to around 70 degree range.
Heat indices should reach the 90s each day in many locations.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
ISSUED AT 744 AM EDT TUE AUG 23 2016

Areas of dense valley fog have led to variable conditions across
the area this morning, with SJS dropping to MVFR at times. The
fog should begin to dissipate around 13Z this morning. Once this
occurs, VFR conditions will prevail for the remainder of the day
as high pressure gradually slides off to the east. MVFR fog will
be possible again late tonight at LOZ, SME, and SJS as return
flow begins ushering in more humid air. Some non TAF sites will
likely have some IFR vis in fog between 6Z and 12Z. Winds will
generally be light and variable through the period.

&&

.JKL Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...JVM
SHORT TERM...JVM
LONG TERM...JP
AVIATION...JVM/JP



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