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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

                            
000
FXUS63 KJKL 210449
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1249 AM EDT Wed Aug 21 2019

.UPDATE...
Issued at 1249 AM EDT WED AUG 21 2019

Overall the forecast looks on track, with only minor adjustments 
to get the hourly temperatures back in line as a result of the 
outflow progressing south. The CAMs are adamant in firing off
convection toward dawn across the southeast, but don't think this
will be that robust given the lack of instability. All grids sent
to NDFD.

UPDATE Issued at 954 PM EDT TUE AUG 20 2019

Outflow boundary has shifted into southeast Kentucky with some
ongoing showers continuing ahead of this boundary. Activity is
starting to fade with the loss of daytime instability, but a few
showers will continue over the next hour or so before this
activity shifts southeast and weakens further. This will provide a
fairly quiet overnight period. However, CAMS continue to support
some redevelopment across a portion of east Kentucky towards 08z
or 09z. Given some MUCAPE holding its ground in southeast
Kentucky, cannot rule out some redevelopment late tonight, and
thus, will bring some low end pops back into the forecast at this
time. Most areas will stay dry through the night. Rain chances on
Wednesday look to remain fairly sparse as well based on the latest
model guidance suggesting a quieter day may be seen across the
area.  

UPDATE Issued at 745 PM EDT TUE AUG 20 2019

Several boundaries continue to be the focus for showers and
storms. The first one is from Lawrence county southeast to Bell 
and Knox county. Outflow from more organized earlier day 
convection is spread into our western counties, but this outflow 
is running into an area already worked over from earlier 
convection. Thus, convection associated with this boundary has 
shifted more southward and that trend will continue over the next 
few hours with rain chances gradually ending from northwest to 
southeast as this outflow continues to push southeast. The outflow
could stall somewhere in southeast Kentucky and could led to 
redevelopment later tonight or tomorrow, but will focus more on 
that later, keeping some rain chances in late tonight and tomorrow
to account for that potential. Otherwise, looks like a period of 
drier weather will be seen overnight.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 431 PM EDT TUE AUG 20 2019

A closed low to our SE and incoming shortwave are both impacting the 
CWA today. Once our CAP was reached, showers and thunderstorms 
starting quickly popping up across the CWA early this afternoon. 
However, with very little wind aloft, there is no steering flow and 
storms are not moving very quickly...rather pulsing up, becoming 
strong, and then collapsing near their origin. On the converse, a 
strong MCS is diving SE from Illinois this afternoon, but models 
continue to show a diminishing trend as the system reaches Kentucky. 
The latest CAMS show the line reaching the western CWA between 23 
and 0Z, and falling apart around the same time, with only isolated 
to scattered showers and thunderstorms expected across the CWA 
through 3Z. Since there has been good agreement between the CAMs 
throughout much of the day concerning the diminishing of this line 
and mostly dry conditions thereafter through 6Z, did not include 
much in the way of pops during this time period.

However, after 6Z, the HRRR and NAM12 both point at another round of 
showers and thunderstorms developing across the CWA heading into the 
early morning hours as the above-mentioned shortwave moves across 
the CWA. Coverage will increase to scattered across the CWA 
throughout the day as we increase our instability with daytime 
heating. Still expecting hot temperatures, with heat indexes near 
100 degrees, perhaps only a few degrees cooler than today.  

Wednesday night, heights will begin to lower across the state as a 
closed upper level low moves SE across eastern Ontario and western 
Quebec. A cold front is also forecast to shift southward towards the 
state, with scattered showers and thunderstorms expected to continue 
throughout this overnight as a result. A more focused east to west 
oriented band may develop across the central portion of the CWA 
according to the latest CAMs.  

Given the cloud cover both tonight and tomorrow night, temperatures 
will remain quite mild. Lows will be around 70 each night, perhaps a 
2 to 3 degrees cooler in the deepest valleys. 

.LONG TERM...(Thursday through Tuesday)
Issued at 420 PM EDT TUE AUG 20 2019

The models are in fair agreement with the upper level pattern 
through much of the extended. A deep northern stream trough will 
progress over the northeastern CONUS, with zonal flow over 
Kentucky. Ridging will then take hold over the northeastern 
portion of the country, as well as a trough over the north-central
CONUS, for late weekend into early next week. 

At the surface, a cold front will approach the Commonwealth early
Thursday. By the afternoon, the front will slow and eventually 
stall over the state. This front will linger through Friday before
moving off to the south for the start of the weekend. MUCAPE 
values from GFS model soundings average about 2500 J/kg Thursday 
and Friday afternoons. Therefore, the better chance for showers 
and storms is expected from Thursday through Friday.

High pressure will then build over the northern portion of the 
Great Lakes and northeastern CONUS through Monday. By Tuesday, 
another system over the Plains will progress eastward, with a warm
front slated to move over western Kentucky early Tuesday. This 
pattern will keep daily chances of showers and afternoon/evening 
storms for eastern Kentucky through the end of the forecast 
period.

High temperatures will be in the mid 80s Thursday, but FROPA will
cause highs to only be in the low 80s through Saturday. Highs 
will then gradually increase to be in the mid 80s by Tuesday. Lows
will generally follow a similar pattern, beginning in the upper 
60s Friday morning. Lows will then drop to be in the mid 60s 
through Sunday before returning to the upper 60s Tuesday morning.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 745 PM EDT TUE AUG 20 2019

While the majority of the period will feature VFR conditions,
there is some small potential for a few showers or storms late
tonight or tomorrow, but confidence is low on coverage and
location to include anything in the TAFs at this time. Thus, will
run with VFR TAFs for now. Light winds will be seen through the
period.

&&

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

$$

UPDATE...DJ
SHORT TERM...JMW
LONG TERM...CGAL
AVIATION...KAS