Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 240532
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
132 AM EDT Mon Sep 24 2018

.UPDATE...
Issued at 1113 PM EDT SUN SEP 23 2018

We are starting to see isentropic ascent lead to some radar
returns developing across the Cumberland Plateau areas. This rain
should continue to expand through the rest of the night and have
updated pops accordingly to match the trends. Looks like a very
damp night setting up for the northwestern portion of the forecast
area. Unfortunately, these are areas that saw the heavier rain
earlier today. We will have to monitor for potential flooding
later tonight. Kept precipitation stratiform tonight associated
with the isentropic ascent with the frontal boundary.

UPDATE Issued at 827 PM EDT SUN SEP 23 2018

Most of the rain has dissipated as expected this evening. However,
as the front starts to lift back to the north tonight, we should
see precipitation redevelop, particularly across the north.
Updated rain chances to diminish them for several hours before
bringing in some higher rain chances a bit later on.

UPDATE Issued at 648 PM EDT SUN SEP 23 2018

Rainfall rates have fallen off considerably in the last few hours.
Had planned to let the watch go early. However, looking at hi-res
model guidance for later tonight shows another round of rain
expected to impact the northern portions of the forecast area.
Thus, instead of letting the watch expire, will go ahead an extend
a portion of the watch through 21z on Monday to capture this next
round of rain, especially considering how saturated the ground is
presently. Rainfall amounts have also been increased per WPC
guidance. Finally changed to stratiform precipitation given more
stable precipitation expected through tomorrow morning.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 400 PM EDT SUN SEP 23 2018

19z sfc analysis shows the stalled cold front just south of
eastern Kentucky with plenty of moisture continuing to stream
northeast along it and into the area. This brought heavy rains to
most of the CWA with some incidents of low level and flash
flooding today. Skies were overcast while winds were mainly light
and variable. Temperatures at 3 pm vary from the low 60s northwest
to the lower 70s in the south while dewpoints are nearly the same
as dry bulb readings at each site. Any thunder has stayed south
of the area so far - though convection is possible in the far
southeast through the rest of the afternoon. The heavier showers
are exiting in the far east with trailing lighter rains slowly
diminishing from the west. Will go ahead and keep the Flash Flood
Watch going for a few more hours until the rains of any
significance are gone.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict Kentucky in between
strong ridging to the southeast and troughing to the northwest.
Between these features southwest flow will carry a series of
shortwaves across the area are running east basically along the
Ohio River. One of the stronger waves will buckle the flow
slightly as it passes Monday afternoon. During this time the Gulf
of Mexico will be open and continue to pump ample moisture into
the region. With this good agreement have gone with a general
model blend, but did favor the CAMs solutions for the near term
QPF forecast through tonight.

Sensible weather will feature the heavier showers exiting the area
over the next couple of hours and then a lull until the next round
later tonight - mainly in the far west. Some shower and possible
thunderstorms will cross the area on Monday with pockets of heavy
rain a concern. The threat for periodic heavy rains will likely
necessitate a new flood watch with later shifts, but for now will
run with the existing one and issue an ESF addressing the flood
concerns going forward. Otherwise, look for a small diurnal range
given the clouds and rain around - cooler northwest and milder to
the southeast. Additionally, fog will be around through the night
associated primarily with the showers.

Again used the CONSShort and ShortBlend as the starting point for
most of the grids with little adjustments to temperatures through
the period. Again did adjust the PoPs higher in the near term and
per the CAMs solution early this evening.

.LONG TERM...(Tuesday through Sunday)
Issued at 333 PM EDT SUN SEP 23 2018

The extended portion of the forecast begins on Tuesday with an
active pattern in place. At the start, a ridge will be in place
over the eastern CONUS just off the coast as a broad longwave
trough will push east through the Great Lakes. This trough will
push a shortwave through the region for Tuesday and into
Wednesday. Ahead of the front will continue to be heavy rainfall
at times as the model soundings suggest a saturated sounding for
both Tuesday and Wednesday afternoon with PWAT values in the 1.80
to 1.90 and modest instability. Concerning Tuesday evening into
the night, a potent cold front will push through Kentucky. While
the instability seems to be lacking for this feature due to the
persistent convective activity ahead of the front, the winds aloft
with the front may develop a squall line type of set up. Thus
with SPC, mentioning this for Tuesday afternoon and into Tuesday
night with the front passing through, will mention some strong
thunderstorm wording with a wind gust potential in the HWO.
However, once again, lingering cloud cover will hinder the severe
threat.

As is the case for the past week, this cold front will begin to
stall against high pressure over the east and drape across
southeastern Kentucky again. This will again provide a focal point
for continued afternoon convection Wednesday evening through
Thursday night. This set up will mainly be over the southeast with
continued rainfall potential. High pressure is expected to move into
the area by late Friday and Saturday. Models seem to agree on the
overall pattern heading into next weekend. Overall, a cooling trend
is expected for the extended with a flood potential early in the
period. A small severe wind is also possible Tuesday night.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 132 AM EDT MON SEP 24 2018

Some areas in the south are seeing VFR to MVFR at times such as
LOZ/SME as a warm front advances northward. We are still seeing
IFR or lower north of the front and these will slowly erode
through the overnight into the afternoon today. The other issue
for the TAF cycle will be the potential for rain showers
particularly as we move into the dawn hours. These will lead to
lowering VIS from time to time through the afternoon today. There
could be some instances of isolated thunderstorms this afternoon,
but for now left out of the TAFs. The winds will be light for the
most part through the TAF period.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through this afternoon for KYZ044-050>052-
058>060-068-069-079-080-083-104-106>109-111-112-114-119.

&&

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...SHALLENBERGER
AVIATION...DJ


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