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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

FXUS63 KJKL 201141

National Weather Service Jackson KY
741 AM EDT Tue Aug 20 2019

Issued at 741 AM EDT TUE AUG 20 2019

The models are struggling with convective evolution upstream this
morning and that will have implications on our convective coverage 
later this afternoon and evening. The 06Z HRRR was strange in 
showing the convection going more east and then outflowing 
southward toward KY and the GFS dives the complex more southward 
into MO. The generally progression right now would suggest some 
where in the middle, which falls more in line with the SPC 
outlook. Again given the uncertainty will remain where we are for 
now and let further updates handle afternoon and evening 


.SHORT TERM...(Today through Wednesday)
Issued at 357 AM EDT TUE AUG 20 2019

We remain under the influence of a surface high off to the east
and ridging nosing in from the southwest. This will lead to
another hot and muggy day across eastern Kentucky, with the 850mb
temperatures in the far east approaching 22C. We should be more 
on the muggy side given the better moisture return, and this
should lead to slightly lower temperatures from yesterday. Given
this thought NBM was reasonable based on the pattern over the past
couple of days, but still think the dewpoints are a little on the
higher side. Either way should still top out in the lower 90s for
most spots. There is the potential for afternoon convection as 
the ridge does back off slightly, as a shortwave approaches the 
Ohio Valley later in the day.

The initial convection will fire along the higher terrain in 
general, but all eyes turn to southeastward propagating MCS that 
is already developing across IA this morning. The CAMs show this 
feature becoming more cold pool dominant as it tracks into 
Kentucky, but the outflow generated would have the potential to 
fire off additional convection underneath MLCAPE values around 
1000 to 1500 J/kg across our area. However, the timing would be 
more in the late afternoon and evening and this could lead to a 
lesser severe weather threat this far east. Thus SPC maintains the
marginal risk for severe weather and this would translate to more
isolated instances of severe weather.

The shortwave will move across the Lower Ohio Valley by around 
06Z and thus maintained some PoPs overnight as a result. The issue
becomes more mesoscale processes after this and will maintain a 
more slight to chance PoP forecast through Wednesday. Did keep 
the temperatures elevated, but not quite as warm given the 
potential for more cloud cover, unknown on convective coverage, 
and more suppressed upper level ridge.

.LONG TERM...(Wednesday night through Monday)
Issued at 500 AM EDT TUE AUG 20 2019

The models are in good agreement with a fairly amplified long wave
pattern to remain in place across the CONUS to start the period.
A sharper trough axis will cross the Great Lakes/Ohio Valley
regions Wednesday night through Friday, shunting an upper level
ridge towards the western Atlantic and along the Gulf Coast. A
cold front will drop southeast and eventually stall across the 
Tennessee Valley, allowing for a return of unsettled weather 
across eastern Kentucky. 

The front will become more diffuse into this weekend and early 
next week; however, troughing will be maintained aloft across the 
Ohio and Tennessee valleys, keeping the threat of at least 
diurnally driven convection going across our area each day. The 
models do continue to differ with the frontal timing, with the GFS
more progressive, while the ECMWF depicts a slower solution. Have
stuck fairly close to the blended solution to account for this
uncertainty. The overall best chance (likely PoPs) will be 
Thursday through Friday, as the front crosses the Commonwealth.
PoPs will then become more diurnally influenced this weekend and
into early next week, with generally weaker forcing in place.
Temperatures will average near normal through the period, with 
highs generally in the low to mid 80s and lows in the 60s. 


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

We are beginning the period mostly VFR, with a couple of sites
advecting fog in this morning. The fog will burn off around 13 to
14z and mostly clear skies will be the story until more cumulus 
form later in the day. There remains a fair amount of uncertainty
related to upstream convective evolution and therefore only went 
VCTS at the TAF sites later this afternoon and evening time 
frame. The winds will remain light generally out of the south and 
southwest through the TAF period.