Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 241946
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
346 PM EDT Wed May 24 2017

.UPDATE...
Issued at 300 PM EDT WED MAY 24 2017

Updated the near term grids with the issuance of the tornado
watch. Added severe wording to the wx grids and timed the storms
via radar trends and latest from the HRRR. Also tweaked sky cover
and the hourly T/Td based on obs and trends. These have been sent
to the NDFD and web servers along with an updated set of ZFPs and
HWO for the tor watch.

UPDATE Issued at 1140 AM EDT WED MAY 24 2017

15z sfc analysis shows a seasonably deep, and stacked, low moving
through the Tennessee Valley. The warm frontal structure with
this is lifting northeast into eastern Kentucky with an associated
cluster of showers and embedded thunderstorms. This first batch
should go through relatively benign, but any `dry slotting` behind
this initial band would open up the opportunity for increasing
instability and the development on more organized and potentially
severe storms given the favorable wind profile and cold pool
aloft. We will monitor the situation through the early afternoon
with a particular focus on clearing and thinning potential in the
cloud cover. Temperatures currently are in the upper 50s to lower
60s with the rain and closer to the mid 60s outside of it with
dewpoints nearly the same. Winds are light and variable away from
any thunderstorm. Have updated the forecast to fine tune the PoPs,
QPF, and wx through the afternoon per radar trends and the latest
HRRR. Also, touched up the T and Td per the latest obs and
trends. These have been sent to the NDFD and web servers along
with an updated ZFP.

UPDATE Issued at 644 AM EDT WED MAY 24 2017

The latest surface analysis shows that the deepening surface low
near the TN/OH Valley will track NNE through the day. The HRRR
suggest there will be multiple rounds of showers and
thunderstorms, but differing solutions are offered up by other
CAMs. Given will leave the POPs as is until better overall
consistency and trends are seen. Based on the radar trends the
lead shield of showers and thunderstorms will progress into the
Lake Cumberland region by around 13Z and far east by 16Z. Severe
risk concern is still in place owing seeing destabilization this
afternoon.

&&

.SHORT TERM...(Today through Thursday)
Issued at 410 AM EDT WED MAY 24 2017

Surface analysis shows an area of surface low pressure continues
to deepen across Middle TN this morning. This as an upper level
wave in the lower MS Valley based on WV SAT rides NE providing
plenty of forcing for ascent across the TN and OH Valley. This
will also drive the aforementioned surface low pressure NNE
likely just NW of the CWA. This will probably drive a more
occluded front across the region and lead to a solid chance of
showers and thunderstorms from late morning into this afternoon.
The low track certainly has our attention, as it would favor
backed winds near the surface. The real issue at hand will be the
large scale forcing could inhibit building any instability this
afternoon with more debris clouds streaming into the region.
However, despite the caveat if we do see clearing and subsequently
more instability organized convection would be likely given ample
shear, with effective values running in the 30 to 40-knot range.
Also the low level backing mentioned above would combine with low
LCLs and effective SRH approaching 200 m^2/s^2 leading to a
isolated tornado risk. However, the main risks with any stronger
storms that could get going would be damaging winds and large
hail given the potential for rotating updrafts. The CAMs remain
complicated and solutions continue to differ probably owing to the
large scale ascent. The HRRR TLE does offer a shot of seeing
severe hail, but the CIPS are lack luster when it comes to climo
for this setup. Also given the deep moisture also can not rule
out the potential for isolated instances of flash flooding.

This upper level closed low will continue to wrap up today and
deepen across the Ohio Valley. The low pressure will track north
and this will lead to a lull in the precipitation this evening.
Did not go no POPs tonight but would not be surprised if that is
the case. However, this system will become vertically stacked
across the Ohio Valley. This will send an area of PVA and low
level convergence SE toward the region by dawn Thursday. An area
of showers will accompany this area of lift and ride across the
region on Thursday. Then surface pressure and height rises are
left in the wake.

Temperatures today will be dependent on clearing, but lower 70s
will probably be the story. Did hedge below the blended guidance
Thursday given the lowering 850mb temps and cloud cover.

.LONG TERM...(Friday through Wednesday)
Issued at 346 PM EDT WED MAY 24 2017

The blended model data was suggesting that after a dry day on
Friday, eastern Kentucky will be in for a period of wet weather
from Friday night through Monday, with another period of rain
possible on Tuesday and Tuesday night. The wettest period looks to
be from Saturday afternoon through Sunday evening, when it appears
that a frontal boundary will stall across the area. Scattered to
numerous showers and storms will possible during this time.
Temperatures during the extended should be running at or slightly
above normal, with daily highs ranging from the upper 70s to lower
80s, and nightly lows in the mid to upper 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 230 PM EDT WED MAY 24 2017

It looks like multiple bands of convection will be crossing the
area through the evening with thunderstorms possible at all the
TAF sites. Initially the eastern ones will see storms with the
west having a round between 19 and 22z. Some of these western ones
may make it east into the JKL/SJS sites toward sunset, but
uncertainty is high with the evolution and progression of this
next band for the CWA. Following the convection later this
evening, cigs will fall to MVFR or lower through the night with
more scattered showers and less organized convective development.
Outside of any storms winds will be light and variable.

&&

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

$$

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



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