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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

                            
000
FXUS63 KJKL 240641 AAC
AFDJKL

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

.UPDATE...
Issued at 240 AM EDT SAT AUG 24 2019

Only minor adjustments have been made to hourly temperatures and
dewpoints based on recent observations. Otherwise, no changes were
needed as the previous grids had sky cover and small pops near the
TN/VA/KY handled well compared to satellite and radar trends.

UPDATE Issued at 1104 PM EDT FRI AUG 23 2019

A patch or two of very light rain remains near the TN border, and
a token 20% POP is continued in the forecast there. Otherwise, the
forecast is on track with drier air and clearing skies moving in
from the north. 

UPDATE Issued at 709 PM EDT FRI AUG 23 2019

Except for a few showers near the TN border, measurable precip 
across the forecast area has ceased. Have trimmed the POP back for
this evening, only keeping precip in the forecast in the extreme 
south.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 406 PM EDT FRI AUG 23 2019

Scattered showers and a few thunderstorms have been the main 
story this afternoon as a cold front slowly moves southward over 
the state. However, lightning has been fairly minimal today. In 
fact, model soundings have shown less than 500 J/kg of CAPE this 
afternoon. Expecting the potential for storms to decrease early 
this evening, with shower activity also dwindling later this 
evening as the front moves to the south of the state. A mostly dry
night will then be on tap, with some patchy fog development 
possible particularly for areas that saw rain today. Any fog will 
then dissipate with the sunrise tomorrow morning.

An upper level trough over the northeastern CONUS, as well as 
zonal flow over Kentucky, will give way to a large northern stream
ridge for the start of the weekend. At the surface, high pressure
will build over the Great Lakes and the northeast. This pattern 
will lead to a mostly dry day for Saturday. However, a surface 
inverted trough over the Appalachians will make showers and a 
storm or two possible along the Virginia border tomorrow 
afternoon. Mostly dry conditions will then continue overnight 
Saturday into early Sunday; although, a shortwave trough will 
advance towards the Ohio Valley for early Monday.

Due to FROPA and rain showers, temperatures in the north have 
only reached the lower 70s. Temperatures in the upper 70s to lower
80s in the south have led to a few isolated thunderstorms this 
afternoon. Lows generally in the mid 50s to lower 60s are then 
expected overnight tonight. Below normal temperatures will 
continue tomorrow afternoon, with highs in the upper 70s to around
80 degrees likely. Lows into Sunday morning will be in the upper 
50s to lower 60s, with the far eastern valleys likely to be cooler
due to clearing skies and light winds.

.LONG TERM...(Sunday through Friday)
Issued at 331 PM EDT FRI AUG 23 2019

The extended portion of the forecast begins on Sunday with a
building ridge over the western CONUS through the period. This 
will be coupled with a prolonged period of overall troughing over 
the eastern CONUS. A strong jet stream will shift southeast along 
the Front Range and then eastward into the Mid MS River Valley. 
This will redevelop a strong shortwave trough into the Upper 
Plains as it shifts east into the Great Lakes. This occurs as 
further building of the ridge continues over the West Coast. This
deepening trough will set up again over the Great Lakes and OH 
Valley through the rest of the extended. This combined with 
weakened ridging over the southeast CONUS will continue to feed 
moist tropical air into the OH and TN Valleys. 

Closer to the surface, a lingering boundary along the TN and VA 
borders will be a focus of convection again. This will be the case 
as a shortwave tracks along the western end of the boundary over 
the Mid MS Valley. The mentioned jet streak aloft will be nosing 
into this region. As a result, surface low pressure will develop 
and shift east as the boundary along the TN border becomes a warm 
front with ample warm and moist air advecting northward. This 
setup will bring a good shower and thunderstorm chance for Sunday 
and into Monday morning. A lack of instability will make for 
mainly showers for the rest of Monday. Heading into Tuesday, as 
mentioned earlier, a strong shortwave once again develops and 
pushes into the OH Valley. This feature will push a cold front 
into the area for Tuesday with a renewed threat of showers and 
thunderstorms. Just like the previous setup, the boundary stalls 
along the TN and VA border giving a continued chance or showers 
and thunderstorms for Wednesday as well before high pressure 
shifts into the area. Thursday could prove to be a dry day as the 
NBM cam in with only pops between 15 and 20 percent. With
coordination, decided to make Thursday a dry forecast to end the
extended. 

The extended shows some hints at cooler weather but upon further
review, the max temps may still be a couple degrees above the
reasonable trends for the NBM. As well, instability heading
through the extended may be in question as the GFS soundings are
lacking through the latter half of the extended. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 225 AM EDT SAT AUG 24 2019

VFR was in place at the TAF sites as drier air continues to slowly
advect in at lower levels on ENE to NE flow. Some initial MVFR 
was present south of the TAF sites nearer to the TN and VA borders
and even IFR for elevations above 2500 feet. Gradual improvements 
should occur in these more southern locations through 12Z to 15Z 
into the VFR range with VFR persisting elsewhere as high pressure
continues to build in. Isolated convection cannot be ruled out 
17Z to 23Z along the VA and TN borders where the greatest low 
level moisture will linger, but the TAF sites will remain dry.

&&

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

$$

UPDATE...JP
SHORT TERM...CGAL
LONG TERM...SHALLENBERGER
AVIATION...JP