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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

                            
000
FXUS63 KJKL 241156 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
756 AM EDT Sat Aug 24 2019

.UPDATE...
Issued at 750 AM EDT SAT AUG 24 2019

Low and mid levels clouds have cleared or at least scattered out 
generally from Somerset to London to Jackson to Prestonsburg and 
north with clouds persisting further south. Temperatures have
dropped off into the mid to upper 50s from near the Mtn Pkwy and 
north with 60s further south. Some minor adjustments were made to
sky cover based on satellite trends with some adjustments to
temperatures based on recent observations. Overall, no significant
changes were needed at this time.  


&&

.SHORT TERM...(Today through Sunday)
Issued at 425 AM EDT SAT AUG 24 2019

Early this morning, a mid and upper level trough was located from
the Canadian Maritimes south into the Northeast and then 
southwest into the eastern Great Lakes and OH Valley region. 
Meanwhile, mid and upper level ridging was centered in the
northern MS Valley region. Further west, a trough was moving from
the Northern Rockies and into the western High Plains. Weak
shortwaves were moving east from the Southern Plains to the
southeast. At the surface, a cold front has settled south of
Interstate 40 corridor and has become generally stationary. A few
showers have occurred overnight nearer to the TN and VA borders,
though at this time, these are exiting to the south and east into
VA. North to northeast low level winds around sfc high pressure 
centered over the Great Lakes are advecting drier air into the 
area Low and mid level clouds have cleared generally north of the 
Mountain Parkway and temperatures there have dropped into the 50 
in the valleys. Some valley fog has already formed or should soon 
form in those locations given upstream nighttime cloud mircophyics
RGB trends in portions of WV and OH. 

Today, the upper level ridge axis will move into the Central Great
Lakes by evening while the center of the sfc high shifts toward
the St Lawrence Valley. Initially, low and mid level clouds will 
be decreasing as a shortwave departs. Any valley fog across the 
northern portions of the area should dissipate by 9 to 10 AM EDT.
The upper ridge and the sfc high will dominate the weather over 
the bulk of the Commonwealth today. However, inverted troughing 
should develop over the Appalachian region today per guidance. 
Deeper lower level moisture should linger in its vicinity and 
south. With daytime heating and weak shortwaves passing east 
generally south of East KY, minimal instability/CAPE should 
develop in the afternoon to early evening. Weak lapse rates in the
mid levels/capping is expected to be sufficiently strong to keep 
thunder chances south and southeast of East KY. A few showers will
be possible nearer to the VA and TN borders over a small portion 
of the area generally from the Big South Fork NRRA to Pine 
Mountain ridge and south including the Black Mountain area. 
Elsewhere some pancake cumulus will be possible in the afternoon. 
Temperatures should reach the upper 70s to lower 80s outside of 
the highest terrain. 

High pressure will remain dominant tonight into early on Sunday though
the mid level ridge axis will move east of the area by Sunday
morning. River valley fog should develop tonight particularly in
the east where skies will be mostly clear early and clouds late at
night should mostly be high. This fog should dissipate early on
Sunday morning. Meanwhile, the shortwave trough currently in the 
Northern Rockies/western High Plains vicinity will move east and 
near the Mid MS Valley on Sunday morning. With the surface high 
also moving further north and east of the area return flow of 
moisture will begin, and be more significant west of I 75 nearer 
to the Lake Cumberland vicinity. Locations further east will 
experience some downsloping as well. The GFS appears to be a fast 
outlier on moisture return and thus has chances for convection 
further east than much of the guidance. It appears to have slowed 
a bit from previous runs, but model blend pops have generally been
trending toward lower pops or even to dry across the central and 
eastern portion of the CWA. Overall, held onto likely pops in the 
southwest though opted for more a gradient in pops from west to 
east for Sunday afternoon. With daytime heating, enough 
instability may develop for isolated to scattered storms near 
Lake Cumberland with chances rather minimal further east. With 
more cloud cover and precipitation in the area, highs should 
generally be colder nearer to Lake Cumberland and warmest nearer 
to the WV border.

.LONG TERM...(Sunday night through Friday)
Issued at 245 AM EDT SAT AUG 24 2019

Gradient will tighten up between a surface ridge to our northeast
and a developing trough over the northern plains Sunday night 
into Monday. The better low level jet will remain to our west with
the low level flow across eastern Kentucky likely staying 
southeast through Monday. Models are starting to catch on to 
better downsloping flow potential and lesser precipitation 
chances, especially in the east and southeast Sunday night through
Monday. Lack of any forcing should prevent precipitation chances 
from getting to the east. However, closer to the jet in central 
Kentucky, some showers could impact areas in our west. Thus, will 
go with a gradient in pops through this period with high 
chance/likely in the west trailing off to nothing in the east and 
southeast. 

A cold front will push into the Ohio river valley by Monday night
and Tuesday, but the better forcing and low level convergence will
remain to our northwest during most of this period. Thus, not sure
if we will have enough to support precipitation chances during
this time in eastern Kentucky, but some residual showers/sprinkles 
from upstream areas could drift across the area Monday evening. 
Otherwise, could see a dry stretch from Monday night through early
Tuesday afternoon at a minimum. The cold front will eventually 
drop southeast across the area Tuesday evening and night with 
showers and perhaps a few thunderstorms pushing across the area. 
Instability and shear are not that great, so doesn't appear to be 
a severe threat at this time. In fact, that is why we may struggle
to get any thunderstorm activity on Tuesday. As the front sinks 
southward Tuesday night, precipitation chances will gradually end
from north to south with perhaps a few stray showers holding on 
in southeast Kentucky into early Wednesday morning. 

Models are in pretty decent agreement from Wednesday through 
Friday with high pressure firmly in control across the region 
leading to dry weather and very pleasant conditions. Dewpoints 
will likely reside in the 50s through the period, supporting 
morning lows starting off in the low to mid 50s each morning from
Thursday through Saturday. Highs around 80 seem reasonable each 
afternoon. 

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 750 AM EDT SAT AUG 24 2019

VFR was in place at the TAF sites at issuance as drier air 
continues to advect in at lower levels on ENE to NE flow. Some 
initial MVFR persists south of the TAF sites nearer to the TN and
VA borders and even some initial IFR for elevations above 2500 
feet. Gradual improvements should occur in these more southern 
locations through about 16Z into the VFR range with VFR 
persisting elsewhere as high pressure continues to build in. 
Isolated SHRA cannot be ruled out 17Z to 23Z along the VA and TN 
borders where the greatest low level moisture will linger, but
most of the area including the TAF sites will remain dry. Winds
will average out of the northeast to east through the period at
less than 10KT. Valley fog may develop by 6Z, with some MVFR to
IFR reductions though this is not expected to affect the TAF
sites.

&&

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

$$

UPDATE...JP
SHORT TERM...JP
LONG TERM...KAS
AVIATION...JP