Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 232011

National Weather Service Jackson KY
411 PM EDT Wed May 23 2018

.SHORT TERM...(This evening through Thursday night)
Issued at 411 PM EDT WED MAY 23 2018

As of mid afternoon, an upper level ridge of high pressure
extended from the eastern Gulf of Mexico and Florida northwest
into the MS Valley. At the surface, an area of high pressure was
centered over the Great Lakes region. Meanwhile the boundary that
crossed the area last night continues to push farther southeast
and east of the area and extended from the mid Atlantic states
into the Appalachians and then west into the TN and MS Valley
regions. Cumulus has gradually been mixing out this afternoon as
drier air continues to advect into the region.

The axis of the upper level ridge is expected to approach the
area from the west through Thursday. Meanwhile surface high
pressure will remain in control tonight. With the high in place,
temperatures should reach the mid to upper 50s in the valleys or a
few degrees below current dewpoints. In addition, the ground is
rather moist from recent precipitation. With clearing skies and
light winds, the stage should be set for valley fog formation
tonight. In the deeper eastern valleys and river valleys, this
fog should become dense overnight. This fog should lift and
dissipate through 9 to 10 AM.

Meanwhile, the surface high is expected to move east and be
centered along the mid Atlantic to northeast US coast by the end
of the day. As this occurs, moisture is expected to return north
especially closer to the crest of the Appalachians as suggested by
guidance. Some cumulus development is expected in all areas, but
locations further north and west should generally be capped by the
drier airmass in place. Despite weak forcing, sufficient moisture
should return for mainly isolated showers and even a thunderstorm
to develop near the VA border generally after 1 PM. The GFS and
NAM both develop convection in the vicinity of Harlan county and
some recent convective allowing model runs also develop convection
in this area. Outflows from the convection could lead to activity
as much as a couple of tiers of counties north into the southeast
KY. Any showers and thunderstorms should wane on Thursday evening.
Some valley fog should again develop Thursday night, however,
dense fog is expected to have less of an areal extent.

.LONG TERM...(Friday through Wednesday)
Issued at 347 PM EDT WED MAY 23 2018

The upper level reveal the ridge will be in the process of
breaking down as a upper level wave develops across the Upper
Midwest. This will continue to weaken the ridging and bring more a
shortwave pattern into the region. Then we turn our attention to a
developing tropical system in the Gulf of Mexico. Surface wise we
will see a surface high that was across the Ohio Valley depart to
the east By Friday allowing more moisture to spill back into the
region. This added moisture and eventual interaction with
shortwave energy will keep the region under the potential for
mainly afternoon and evening showers and thunderstorms. The best
chances through the period will generally be closer to the higher
terrain. The aforementioned tropical system will play a role in
how much moisture we will receive and this will be dependent on
the track and overall evolution. That said, the GFS operational
solution is a outlier compared to the ECMWF, Canadian, and most of
the GEFS solutions, with its more eastern track. The better
overall plume of moisture seems to setup across the Carolinas.
Either way it does seem like a increase in moisture could at least
lead to isolated heavy rain issues given the potential for
afternoon convection each day.


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

Cumulus generally between 3 and 5kft were observed across the
region at issuance time, with VFR prevailing. Generally VFR
should prevail for much of the period with high pressure in place
across the region. The only caveat will be fog development
generally after 5Z. The fog should dissipate in all areas by 14Z.
However, this fog should become dense in the deeper valleys and
river valleys. For the TAF sites, some MVFR reductions are
anticipated between 8Z and 13Z at all sites other than SYM. Winds
should remain light and variable through the period.




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