Area Forecast Discussion
Issued by NWS Jackson, KY

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151
FXUS63 KJKL 221812 AAB
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
212 PM EDT Sat Apr 22 2017

.UPDATE...
Issued at 200 PM EDT SAT APR 22 2017

A band of showers is exiting into VA and WV although additional
convection over Central Ky and middle TN should move east
northeast and into East KY through the afternoon. This convection
will move across portions of the region that already received in
excess of two thirds of an inch to 1.25 inches of rain since
around sunrise. With already wet ground in place, new or renewed
high water issues will be possible with excess runoff from this.
Hourly grids were freshened up based on recent radar, short term
model, and observation trends.

UPDATE Issued at 1150 AM EDT SAT APR 22 2017

Hourly grids have been freshened up based on recent radar trends
and observations. This led to inserting a couple hours of lull in
the pops moving from west to east across the area through early
afternoon. Additional rounds of showers will occur in the
afternoon and evening. Recent model trends have been toward lower
rainfall for the remainder of the event for most of the area
though the GFS still has some higher amounts in the watch area
mainly late tonight and on Sunday. However, many of the other
models have lower amounts so confidence is not all that high.

UPDATE Issued at 740 AM EDT SAT APR 22 2017

Did a quick bit of touch up on the grids, primarily to move in the
heavier pcpn a bit quicker with this first wave. This should set
the stage for decent flooding potential across the south with
subsequent waves likely to pose the greatest threat for flash
flooding - though would not be surprised if a few urban and small
stream advisories could be needed for local minor issues with this
wave. Also, fine tuned the T and Td grids per the latest obs and
trends. These grids have been sent to the NDFD and web servers.

&&

.SHORT TERM...(Today through Sunday)
Issued at 325 AM EDT SAT APR 22 2017

07z sfc analysis shows a developing area of low pressure over the
central Gulf Coast to the southwest. A warm front/inverted trough
extends northeast from this stretching across southern parts of
eastern Kentucky. This boundary and points south will likely be
the location of the heaviest rains with this system through the
next 36 or so hours. Currently, showers, mainly light, continue to
propagate over the northern portions of the CWA as they stream off
to the east northeast. Skies are overcast across the area with
just warm clouds noted on satellite. Temperatures vary from near
50 degrees over the extreme northwest portion of the CWA to Low
60s southeast on the other side of that boundary. Dewpoints vary
in a similar manner with some mid 40s seen up north and low 60s
found in the south. The winds overnight show evidence of the front
with north to northeast ones for much of the CWA north of the Hal
Rogers Parkway while to the south and east they are still
southerly.

The models are actually now in excellent agreement aloft through
the short term portion of the forecast. They all depict a slow
moving and evolving upper low closing off and dropping into the
Tennessee Valley. The clustering of the models are impressive and
lends confidence to the overall forecast through 00z Monday. As
such have favored a blended solution with emphasis on the high
resolution models for specific details on PoPs and QPF through
the first 24 hours.

Sensible weather will feature a renewed development of showers,
and even some thunderstorms across the south, this morning as the
next surge of pcpn pushes into the area. This is well depicted in
the HRRR and its timing was generally followed in the grids
through 15z. The initial batch of rain after sunup will target our
central and northern counties moreso than the south, but that
changes by afternoon as the next surge will be focused more over
the Cumberland Valley. Overall, the broad sfc low passing just
south of the CWA during the short term portion of the forecast
will be a source for showers and heavier bouts of rain through
tonight before easing off to the southeast on Sunday. While the
best chances for thunder will be in the south today and this
evening heavy rain will remain a threat in the far southeast
through Sunday afternoon. For this reason, a flash flood watch
will be issued shortly for our southern tier of counties starting
at noon today and running through 4 pm Sunday. Sustained rains
during this event over the headwaters of the Cumberland and
Kentucky Rivers will also raise the specter of river flooding
later in the weekend and into the start of next week.

Temperatures will be on the chilly side through this period with
only the far south seeing readings remotely near normal today.
After highs in the low to mid 50s today, the north could rebound
into the lower 60s on Sunday thanks to the main focus of the rain
being in the south and perhaps some sun filtering through the
clouds in the afternoon. Temperatures tonight will be fairly
uniform in the upper 40s most places - coldest north and milder
south.

Started the grids from the CONSShort and ShortBlend through the
short term portion of the forecast. Did not make much adjustment
to temperatures or dewpoints given the limited diurnal range.
However, did beef up PoPs and QPF from the blend across the south
given the certainty for rain and many surges of shower activity
during this time (thunderstorms early in the event).

.LONG TERM...(Sunday night through Friday)
Issued at 330 AM EDT SAT APR 22 2017

The upper level low will meander up the east coast Sunday night
through Tuesday with mid level heights slowly recovering through
the period as the eastern system slowly pushes farther off shore
into the Atlantic. Some lingering rain chances will hold on
Sunday night, especially in southeast Kentucky before we dry out
early Monday. This will provide a much needed dry period Monday
through Wednesday morning. Temperatures will stay cool into Monday
with highs in the 60s. As return flow kicks in Tuesday highs
should climb back into the 70s.

The next chance of rain will come late Wednesday/Wednesday night
as a shortwave trough drives another cold front across the Ohio
river valley. The front may be shearing out as it crosses the
area, so opted to stay with the lower blended pops as it may not
be a widespread rain event for the area. Regardless, a few
thunderstorms would be possible, especially up in the bluegrass
region. Whats left of the washed out front will lift back to the
north as a warm front by weeks end, with much warmer weather
surging north across the region. This is also about the time our
next system may be taking aim on the area by Friday afternoon, but
some model inconsistencies will keep the uncertainty high with the
late week system.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 210 PM EDT SAT APR 22 2017

Ceilings remain IFR to MVFR in the wake of an area of shra this
morning. Additional shra and even some tsra moving in from the
west and southwest should affect the region through about 1Z with
mvfr to at time brief reductions to ifr vis and or ceilings. A
relative lull in activity should occur across the central and
northern part of the area overnight with mvfr prevailing generally
JKL and SJS south and some VFR in the north. As the upper level
low nears late tonight and on Sunday, additional showers should
develop with MVFR and IFR reductions during the the 11Z to 18Z
period. The post persistent IFR should occur generally south of
an SME to LOZ to JKL to SJS line nearer to the VA border. Winds
should generally remain 10kt or less through the period outside of
any thunderstorms.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Sunday afternoon for KYZ079-080-
083>088-110-113-115>118-120.

&&

$$

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



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