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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

FXUS63 KJKL 230257

National Weather Service Jackson KY
1057 PM EDT Thu Aug 22 2019

Issued at 1057 PM EDT THU AUG 22 2019

A few showers remain, but thunder has died out for the time being
over the JKL forecast area. However, additional thunderstorm
development has begun over south central KY. Mesoscale models
continue to show further development into our area overnight.
Confidence in the details of when/where is not high, but the
general likely POP already in the forecast for the overnight 
hours still looks reasonable, and the only changes at this point
are to blend obs into the forecast.

UPDATE Issued at 855 PM EDT THU AUG 22 2019

Have updated to account for current precip and higher POPs where
it hits in the very near term. Have left the remainder of the
precip forecast intact overnight, with additional showers expected
to develop.


.SHORT TERM...(This evening through Friday night)
Issued at 421 PM EDT THU AUG 22 2019

A cold front is currently located along the Ohio River, and is still 
poised to shift southward into the CWA during the overnight, then 
linger into the morning on Friday before finally dropping south of 
the state during the afternoon. An increase of moisture ahead of 
this system has resulted in showers and thunderstorms across the 
region, primarily across our southern CWA. As we head into the 
evening, expect convection to begin increasing in our north along 
and just ahead of the boundary, with likely pops forecast to spread 
across our entire CWA after 6Z and continue through much of the day 
Friday, while tapering off north of the frontal boundary. As drier 
air works in behind the boundary, expect all precip to dissipate 
from north to south during the overnight hours Friday night. 

According to the latest NAM soundings, the best instability as far 
as CAPE was actually earlier in the day today. However, decent CAPE 
values still remain into the afternoon, and could continue to result 
in some strong storm development. That being said there is still 
very little shear in the low and mid while the storms 
have decent prorogation from winds aloft, they have a hard time 
sustaining and becoming organized. Lapse rates also decrease after 
about 13k feet, especially in the SW this afternoon, so it will be 
harder for storms to grow here. So far we have had several storms 
reach SPS potential, but have not been able to grow and sustain pat 
this point. 

Deeper moisture will continue to work into the region through the 
evening and overnight, with instability and shear expected to 
decrease even more. This has led to a reduction of thunder to just 
chances despite the likely pops throughout the night. The same 
remains true through the day Friday as the front continues its 
journey southward. There may be some decent instability that 
develops south of the front during the afternoon tomorrow, but 
should be fairly short lived as winds begin to shift eastward. Ended 
up just keeping a chance thunder pops in throughout the day. 
Temperatures will also be cooler as a result of the clouds and 
precip, as well as more Wrly and NWrly flow. Highs will range from 
the upper 70s in the north to the low 80s in the south.

Precip will taper off Friday night as the front departs south of the 
CWA, with a complete loss of instability cutting off any further 
thunder potential. Colder northerly flow will also take hold, with 
temperatures expected to fall into the upper 50s (north) to the low 
60s (south). 

.LONG TERM...(Saturday through Thursday)
Issued at 422 PM EDT THU AUG 22 2019

The models are in fair agreement with the upper level pattern this 
weekend and through the start of next week. A northern stream trough 
will almost be through the northeastern CONUS, with ridging taking 
hold over the Mississippi Valley. Expecting this ridge to persist 
for most of the weekend. Another northern stream trough will push 
southeastward from Canada into the north-central CONUS for the start 
of next week, with a progressive shortwave slated to move over the 
Ohio Vally early Tuesday. By midweek, the models begin to diverge in 
solution with how amplified the trough becomes as it continues to 
progress eastward over the Great Lakes.

At the surface, high pressure will build over the Great Lakes and 
northeastern CONUS as a cold front makes its way southward over the 
Tennessee Valley. This pattern will generally persist through the 
weekend. By Tuesday morning, another cold front will advance towards 
the Commonwealth, with high pressure to the east of the state. The 
front will then eventually progress over Kentucky by Wednesday, with 
high pressure building back in over the state for late week. Yet 
another cold front then looks to move southeastward over the 
Mississippi Valley and north-central Plains late next week as well.

Most of the weekend should be fairly dry for most of eastern 
Kentucky, with possible showers along the Tennessee and Virginia 
borders Saturday afternoon. Sunday afternoon could see some possible 
shower and storm chances as an inverted trough forms along the 
Appalachians. Shower and storm chances will then be on the increase 
early next week through midweek due to increased moisture from 
return flow late Monday into early Tuesday as well as the passage of 
the cold front around midweek. There are some model differences in 
regards to the timing of this front, but at this time have favored a 
quicker advancement of this feature.

High temperatures will generally be near 80 degrees for Saturday. 
Highs in the lower 80s will then be the story through Monday before 
rebounding to be in the mid 80s through late week. Low temperatures 
will be in the upper 50s to lower 60s Sunday morning. Lows will then 
generally be in the 60s through Thursday morning.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)

Showers and thunderstorms were affecting some of the western
portion of the forecast area at the start of the period, 
generally between I-64 and the TN border. This was resulting in
localized sub-VFR conditions, and will affect KSYM this evening 
as the precip moves northeast. Outside of the precip, conditions 
were mainly VFR, and that should continue to be the case until 
late tonight. From about 05Z on, conditions are forecast to 
deteriorate from north to south, dropping to IFR or worse just 
about everywhere by around 13Z. Additional showers will affect 
much of the area late tonight and on Friday, with perhaps a few 
more scattered thunderstorms. Timing/location is too uncertain to 
warrant more than vcsh in TAFs, except in southern portions of the
area (including KSME AND KLOZ) on Friday afternoon, when/where 
showers are included as the prevailing condition. Diminishing 
precip and improving conditions should begin to arrive from the 
north during the afternoon, but probably not make it all the way 
to the TN border before the end of the period.