Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 151157 AAA

National Weather Service Jackson KY
757 AM EDT Sun Sep 15 2019

Issued at 745 AM EDT SUN SEP 15 2019

Valley fog mainly along the larger rivers and largest creeks as
well as area lakes should lift and dissipate over the next couple
of hours. Otherwise, a dry airmass is in place across the area and
this is expected to persist today. The subsidence inversion has
lowered to the level of the crest of Black Mtn this morning with a
23 dewpoint recently observed. As the morning progresses, the
level of the subsidence inversion should rise above the peak of
the mountain. However, this is indicative of a day with
considerably low min rh for mid September and more typical of mid
to late October. The dry airmass will warm quickly today and
temperatures should approach or reach 90 for a couple of hours in
many locations this afternoon.


.SHORT TERM...(Today through Monday)
Issued at 410 AM EDT SUN SEP 15 2019

A mid and upper level ridge of high pressure was centered across
the southeastern Conus and extended west into the southern Plains.
Generally westerly flow aloft is in place across the region at
this time. Further north and northwest, a shortwave trough
working through the Great Lakes. Also at the surface, high
pressure was centered over the mid and Upper OH Valley regions.
Further northwest, a sfc area of low pressure was approaching the
Great Lakes with a cold front extending west across portions of
the Plains. Locally limited river valley fog has developed thus
far per GOES East imagery with some cirrus passing overhead. With
the rather dry airmass in place across the region, valley
temperatures have dropped into the low to mid 50s across northern
sections of the area with upper 50s in valleys further south.
Some of the coalfield ridgetop locations are in the lower 60s.

Today, the upper level pattern is expected to continue to amplify
with the upper ridge building north through the Plains and mid and
upper MS Valley regions. This high will become centered in the MS
valley tonight and into Monday. The upper level flow will become
more northwest by late this afternoon and tonight with this
continuing into Monday. As this occurs the shortwave trough will
continue east across the Great Lakes and into the Northeast
leaving a trough extending south from the Maritimes and into
portions of the Atlantic. Humberto meanwhile is expected to
remain east of the FL east coast today gradually meandering north
and then east away from the southeast US coast. The sfc high will
weaken a bit through today and into tonight, but remain in place
across the Appalachians. The amplifying pattern will also send a
frontal zone south toward the OH Valley tonight and into East KY
on Monday.

Additional valley fog may develop through sunrise this morning
with this lifting and dissipating through around 9 to 930 AM EDT.
A dry airmass will remain across the area today with 1000 to 500
mb mean rh of generally 30 to 35 percent or less or PW on the
order of 0.6 to 0.9 inches. Very little clouds other than some
passing high clouds are anticipated today and the airmass should
warm up quickly today considering the lingering dryness across
much of the area. A rather large diurnal range is expected from
lows this mornings to afternoon highs, especially for valley
locations. Highs should be similar to if not a degree or so higher
than Saturday on average and leaned heavily toward NBM highs. At
this time, highs are expected to fall short of records at JKL and
LOZ. The warm temperatures and dewpoints around 50 or in the lower
50s should result in min rh in the 25 to 35 percent range on

High pressure will remain dominant tonight with some river valley
fog again possible. With dewpoints in the 50s across the area, mid
and upper 50s are expected for some of the normally colder
valleys with low 60s on the coalfield ridges and in more open
terrain areas.

At the same time that the boundary drops into the region on Monday,
500 mb heights are progged to fall a bit with the upper level
flow rather weak. Dewpoints should increase across the area,
especially across the north and northwest where some low to mid
60s will be more common on Monday afternoon. A cumulus field
should develop at the very least, and with the atmosphere not
capped, MLCAPE north and northwest may reach near 1000 J/kg with
MUCAPE on the order of 1500 J/kg or so. Mid level lapse rates will
probably be less than 6C/km, however, and with weak shear despite
the boundary dropping into the area, coverage of showers or any
thunderstorms should be limited as has been the trend lately. Kept
in slight chances for a few hours in the afternoon to early
evening on Monday for the north and northwest where the dewpoints
should be the highest and PW is progged to climb toward 1.5
inches. Further south and southeast nearer to the VA, TN, and VA
borders just some cumulus should develop. Otherwise, the warm
weather will continue with highs outside of the highest terrain
again reaching around the 90 degree mark. Record highs for LOZ and
JKL will again be approached.

.LONG TERM...(Monday night through Saturday)
Issued at 328 AM EDT SUN SEP 15 2019

The extended portion of the forecast begins on Monday night with an
upper level pattern featuring a building ridge in the west as it
then continues to transition eastward. This ridge will increase in
strength as it shifts into the eastern CONUS. In the meantime, a
strong longwave trough will deepen into the Pacific Northwest as
several strong shortwaves are ejected into the northern Plains. A
weak wave beneath the mentioned ridge over the Great Lakes on
Monday night traveling through the OH Valley will extend a weak
boundary into eastern Kentucky for Monday evening. Given the
amount of dry air in place and limited instability, this will only
yield a slight chance of measurable precipitation at best. Will
decide to go dry for Monday evening given the trends in the Euro
and the NBM. The mentioned ridge aloft will shunt the approaching
soon to be Hurricane Humberto just off the east coast and cause
it to recurve into the Atlantic by Tuesday and Wednesday. The mid
level ridging will serve to keep any precip from developing across
eastern Kentucky through the entire extended. Surface high
pressure will remain over the Mid MS Valley on Monday and begin to
drift east into Kentucky through the extended. Concerning the
trend of the model runs, once again the GFS shows tropical
moisture creeping into central Kentucky Thursday, but to a lesser
extent than previous runs. The Euro continues to keep eastern
Kentucky dry. Both models do hint at a trough digging into the
area and a significant front pushing through on Tuesday beyond the
extended. However, no model brings confidence at measurable
precip Tuesday through Saturday so a dry forecast will persist.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)

Surface and upper level high pressure will dominate through the
period with high clouds passing by from time to time. VFR will
prevail through the period at the TAF sites. However along the
rivers, lakes, and larger creeks, initial valley fog with
reductions to MVFR or IFR, will lift and dissipate through 13Z to
14Z. After that time, VFR will prevail in all locations for the
duration of the period with on exception. Valley fog with MVFR to
IFR reductions will again be possible from 7Z through the end of
the period. Winds will remain light.




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