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Area Forecast Discussion (AFD)

Issued by Jackson, KY (JKL)

FXUS63 KJKL 200248

National Weather Service Jackson KY
1048 PM EDT Mon Aug 19 2019

Issued at 1048 PM EDT MON AUG 19 2019

A few showers and storms continue to redevelop across central
Kentucky, but have been staying out of our forecast area through
the evening hours. Mainly clear skies have been seen over east
Kentucky this evening, setting the stage for valley fog later on.
Forecast temperatures are on track, so only minor tweaks planned
to the forecast with no real update planned.

UPDATE Issued at 735 PM EDT MON AUG 19 2019

Last of the showers are dying away with instability decreasing.
This will allow showers and storms to be taken out of the forecast
for the rest of the evening and overnight hours. Forecast is in
good shape, so only thing to update is to remove the rain chances.


.SHORT TERM...(This evening through Tuesday night)
Issued at 405 PM EDT MON AUG 19 2019

19z sfc analysis shows high pressure a bit weaker this afternoon
than yesterday with lower pressure to the west and north. This,
and the warmth at mid levels, has helped to keep the little
convection we have seen so far this afternoon from becoming too
strong or expansive, thus far. The showers been contained in the 
western Kentucky River valley through mid afternoon while high 
clouds seems to have slowed any development in our southeast high 
terrain. Temperatures again made it to the low and mid 90s for 
most of the area with dewpoints up a notch from yesterday in the 
upper 60s and lower 70s sending the heat indices to around 100 
degrees most places. Winds have been light and mostly from the 
southwest today. 

The models remain in fairly good agreement aloft through the short 
term portion of the forecast. They all depict heights holding 
steady over the area as northwest flow brings a strong shortwave 
through the Ohio Valley late Tuesday into Tuesday night. This will
be a ridge rider moving through a divergent environment and 
dampen heights over northeast Kentucky briefly before they start 
to rebound by 12z Wednesday - quickest in the Canadian - from the
expansive southwest ridge. Given this agreement will again favor 
a blended model solution as represented by the NBM - along with a 
healthy dose of the better verifying CAMs in the near term. 

Sensible weather features a very warm evening with any isolated
convective activity dissipating before sunset. Again we will see a
small ridge to valley temperature difference under mostly clear
skies for most of the night before some high clouds could move in
late. The clearing and a bit more boundary layer moisture should
allow for more in the way of fog late tonight - still mainly
confined to the river channels and valleys, though. For Tuesday, 
a more active and less certain weather day will unfold. Hot 
temperatures are again on tap with increasing dewpoints making for
more sultry conditions. Convection will be the big uncertainty as
the heights bump down a bit due to the approach of that mid level
shortwave. This impulse should be enough to develop strong and 
organized storms to the northwest of the area with their 
subsequent tracks and further development potentially pushing 
into our area late in the day. And that is not to rule out some 
more isolated activity through the afternoon as convective 
temperatures are reached but with little in the way of good 
triggers until that influence arrives from the northwest. This 
will have to be watched through the day as a large enough system 
could turn into our area late in the day and tap into some very 
unstable air. The models have not settled on a firm solution here,
yet, though, so have played it conservative in the grids - but 
more substantial storms and coverage are not out of the question 
depending on the upstream development. Barring a large storm 
cluster moving through Tuesday evening and early in the night - we 
should see a similar night to this upcoming one with clearing 
skies and small chances for rain - along with some more river 
valley fog by dawn. 

The NBM was again used as the starting point for all the grids 
with only minor adjustments to temperatures (mostly higher given 
recent trends and underdone drying) at some points along with 
minor ridge and valley differences for tonight and Tuesday night. 
For PoPs, adhered to the diurnal trends until later Tuesday when 
northwest activity and outflows could dominate. 

.LONG TERM...(Wednesday through Monday)
Issued at 454 PM EDT MON AUG 19 2019

The models are in decent agreement in regards to upper level 
pattern through the first part of the long term period. An upper 
level trough, with progressive shortwaves, will make its way over 
the Great Lakes and northeastern CONUS regions into the weekend. A
southern stream trough and northern stream ridge will then 
progress over the eastern CONUS through the weekend; however, 
model solutions begin to diverge by this time. 

Closer to the surface, high pressure to the southeast of the 
Commonwealth will keep chances for showers and a few thunderstorms
Wednesday afternoon. Although the ECMWF and GFS disagree with the
timing of a cold front through the state Thursday, showers are 
expected to increase area-wide. With GFS model soundings showing 
2000 to 3200 J/kg of MUCAPE Thursday afternoon and early evening, 
thunderstorms will be possible as well. This front will then stall
to the south of Kentucky by Friday morning. High pressure will 
build over the Great Lakes and northeastern CONUS, and the front 
will slowly sag south over the southeastern CONUS through the 
weekend. This will keep daily chances of showers from Friday 
through the end of the period, with a few storms also possible 
during the afternoon and early evening hours.

High temperatures will begin in the upper 80s midweek before 
cooling to be near 80 degrees Friday afternoon due to FROPA. Highs
are then expected to rebound to the mid 80s for late weekend into
early next week. Low temperatures will follow a similar pattern, 
beginning in the upper 60s Thursday morning but cooling to near 60
degrees by Saturday morning. Lows will then warm to be in the mid
60s for the start of next week.


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

Mainly VFR conditions and light winds will be seen through the TAF
forecast period, although some valley fog will develop late
tonight. This fog is not expected to impact the TAF sites.