Area Forecast Discussion
Issued by NWS Jackson, KY

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893
FXUS63 KJKL 231741
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
141 PM EDT Sun Jul 23 2017

.UPDATE...
Issued at 141 PM EDT SUN JUL 23 2017

MCV from overnight convection is crossing the area presently with
outflow boundary extending across the area associated with the
overnight convection. The cloud cover from the MCV has really done
a number on our instability out there. However, it still looks
like we should see some modest clearing by mid afternoon, with
temperatures rebounding into the 80s. This should help aid in
convection redeveloping into the late afternoon/evening hours.
While the severe threat is a little more in question now, with
instability very limited, flash flood guidance still remains under
an inch in the north, so no plans to change up the flash flood
watch. CAMS have been very inconsistent through the morning hours
on how things may evolve this afternoon, so confidence not great
this afternoon or evening. It does look like everything should
exit south and east by midnight, with a dry second half of the
night.

UPDATE Issued at 954 AM EDT SUN JUL 23 2017

After seeing the heavy rainfall from last night and looking the
latest CAM runs from this morning which generally all show some
redevelopment across the area this afternoon and evening, have
opted to go with a flash flood watch for the northern half of our
forecast area. Flash flood guidance is running much lower now with
all the heavy rains that have moved through, so it won`t take much
to cause more issues. The watch will be issued for mainly areas
that saw rain overnight. Areas farther south, have more or less
not seen as much rainfall, so guidance remains higher to the
south. Latest HRRR really targets the same areas that got hit last
night, so concern is clearly elevated. RAP targets areas a bit
farther south, but will continue to monitor trends as the day goes
on. Given the generally good agreement on the redevelopment, have
gone above guidance on the rain chances this afternoon and
evening.

UPDATE Issued at 740 AM EDT SUN JUL 23 2017

Latest round of storms are exiting far eastern Kentucky. This will
set up a lull before the next batch moves in or develops over the
area. Have updated the grids with this in mind as well as adding
in the latest T/Td obs and trends. These have been sent to the
NDFD and web servers.

&&

.SHORT TERM...(Today through Monday)
Issued at 420 AM EDT SUN JUL 23 2017

07z sfc analysis shows a washed out front lying through the lower
part of the Ohio Valley. This night a series of storm clusters are
moving generally east along this boundary with outflows from these
storms making it south deep into the JKL CWA. The core of the
strongest storms, and biggest threat for damaging wind gusts and
flooding rains, will be with the main track through northern
parts of Kentucky, but additional strong storms, though more
scattered, will be possible south. Fleming County has borne the
brunt of the storms for the JKL CWA, so far, with reports of wind
damage and flooding there early this morning. As the first
cluster of storms fade out over far eastern Kentucky, the next is
poised to enter from the west. This could bring renewed flooding
to the area as well as a threat for additional wind damage.
Otherwise, temperatures and dewpoints vary across the area based
on where the rain has fallen with both in the upper 60s north and
the south seeing temps in the low to mid 70s with low 70s
dewpoints. Winds outside of the storms and outflows have been
generally from the south to southwest at 5 to 10 mph.

The models are in good agreement on the broad details aloft with
the pattern through the short term portion of the forecast.
However, the determinative factor for sensible weather will be
from smaller scale waves poorly handled by the models so
confidence is low in the specifics from any individual model. On a
broader scale the models do all depict the fairly strong trough
that will move through the Great Lakes and Ohio Valley today with
significant height falls and plenty of energy brushing by to the
north. This northwest flow environment will maintain the threat
for MCS activity through the day before the heights start to
rebound in the trough`s wake later tonight and on Monday. Will
favor a general model blend as a starting point but significantly
lean on extrapolation of current radar trends and the HRRR for
near term details.

Sensible weather will feature continuing showers and thunderstorm
threatening the area through the morning as the next cluster moves
into the CWA. There remains enough instability in place with high
PW air and some decent DCAPE available for downdrafts.
Accordingly, strong storms will continue to threaten flooding
rains and damaging winds at least through dawn. After that the
frontal boundary and left over outflows will set the stage for
more potential storms. The convection and clouds today will keep
temperatures in check compared to the last few. This should
mitigate the heat concerns even though dewpoints will continue to
be high. High pressure will start to build into the area tonight
but not effectively enough to push down dewpoints and PoPs too
far. As a result, scattered storms will still be a concern tonight
and Monday, though to a far lesser extend then this morning and
most of the day.

Used the CONSShort as a starting point for all the grids, though
made some minor changes to point temps today and tonight. Did also
make major adjustments to PoPs and QPF in the near term to better
reflect radar trends.

.LONG TERM...(Monday night through Saturday)
Issued at 320 AM EDT SUN JUL 23 2017

The latest model data indicate that the remnants of a stalled out
frontal boundary will linger across the northern Tennessee valley to
being the extended period. As moisture interacts with this boundary,
or at least what is left of it, isolated showers and storms are
expected to form along it. The best chance for rain to begin the
period should be Monday night, as the front drifts slowly southward
across the region. A few showers and storms may move across portions
of eastern Kentucky along the Tennessee border on Tuesday and
Wednesday, as the front meanders northward toward the area. There
should then be a break from the rain Wednesday night, as the front
finally moves off well to our south. However, a second more well
defined cold front is then forecast by the models to move across the
Ohio and Tennessee valleys Friday night and Saturday. This front may
be strong enough, and have enough moisture interacting with it, to
produce numerous showers and storms across eastern Kentucky going
into the weekend.

Temperatures during the period should start out above normal, with
readings in the upper 80s expected for Tuesday through Thursday. The
temperatures should cool slightly after that, as the second cold
front moves through. We should see high temperatures only making it
into the lower 80s Friday and Saturday due to persistent widespread
cloud cover and repeated rounds of showers and storms during that
time. Nightly lows are forecast to start off in the mid to upper
60s, before cooling to the lower 60s by the end of the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 141 PM EDT SUN JUL 23 2017

Dying MCS has really zapped the daytime warming thus far and thus
will keep thunderstorm chances at bay until after 20 or 21z. It
looks like there will be a narrow window this evening for a few
storms. Otherwise, mainly VFR conditions should dominate the TAF
period. If we can clear out late tonight, we could have to contend
with some valley fog, although no impacts are expected at the TAF
sites.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until midnight EDT tonight for KYZ044-050>052-
058>060-104-106>112-119-120.

&&

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...AR
AVIATION...KAS



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