Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 222054
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
454 PM EDT Sat Apr 22 2017

.SHORT TERM...(This evening through Sunday night)
Issued at 425 PM EDT SAT APR 22 2017

As of mid afternoon, an upper level trough extended from Quebec
south and then southwest into the OH Valley and Mid MS Valley
region. At the surface, an area of low pressure was over the
Atlantic with a cold front to its south and southwest that becomes
wavy or nearly stationary from near the VA Tidewater region west
and then southwest into southern middle TN where a stronger wave
of low pressure was located. Rounds of showers and thunderstorms
continue to move east near the boundary one of which is moving
across the southern part of the CWA in advance of the upper
trough. A steadier rain or drizzle was falling across the more
northern locations. The heaviest rain today has fallen near the
TN and VA borders with the heaviest rain from Bell to Letcher
Counties.

The southwest part of the upper level trough should close off as
it is left behind as the northern portion of the trough departs to
the northeast. The upper level low will meander to southern middle
TN and the northern Gulf Coast states through Sunday evening. The
upper level low should meander further southeast into southern GA
by the end of the period. Meanwhile the surface low is expected to
move across the northern Gulf Coast states through Sunday
afternoon with an inverted trough developing to its north working
east across the Commonwealth tonight through Sunday evening. The
surface low should also move southeast on Sunday night further
away from East KY.

Some right entrance region jet dynamics appears to be aiding the
current round of convection along with some isentropic lift over
the boundary to our south. Near term convective allowing models
appear generally in line with radar trends as convection should
affect mainly the southern part of the area through around
sunset. A relative lull then may ensure for much of the night
until the center of the upper level low closes off and gets nearer
to the region. This and the inverted trough may help focus
another round of steadier rain or moderate showers mainly from the
TN border northeast along the VA border late tonight and into
Sunday. The 12Z GFS has higher qpf with this while the 12Z NAM and
12Z ECMWF have lesser amounts. For qpf stayed closed to the model
blend guidance that was a compromise of the higher and lower
values. If multiple thunderstorms affect the south or the showers
become more intense across the south than the threat for flash
flooding would increase. The counties that have been wettest over
the past 24 to 48 hours are Bell, Harlan, and Letcher along with
parts of Whitley and McCreary. Uncertainty also remains and if the
12Z GFS heavier qpf were to verify the threat for high water and
flash flooding or river flooding would increase. The current
forecast qpf would generally confine the flash flood threat from
Bell to Letcher and perhaps Pike County. Multiple rounds of rain
will contribute to high water and perhaps a downstream point or
two along the Cumberland or Kentucky such as Williamsburg or
Ravenna reaching minor flood stage by the end of the weekend.
Uncertainty does remain.

The qpf from this afternoon through Sunday night is minimal a
quarter inch or less in the north where only lighter showers or
drizzle are expected this evening and on Sunday. More numerous to
widespread rounds of showers will occur to the south especially
nearer to the VA and TN borders. Expected rainfall increases to about
a half of an inch to three quarters of an inch nearer to the Mtn
Parkway and an inch or more along or south of Hazard to or more
south of a Monticello to London to Pikeville line. Amounts near 2
inches are expected from near Middlesboro along the VA border to
near Jenkins. Locally higher amounts are possible and the rainfall
amounts and flood threat will be determined by the evolution of
convection and rainfall rates. At this time, the current areal
extent and valid time of the Flash Flood Watch appear to be in
good shape.

The shower threat will diminish from late Sunday afternoon to
Sunday night even in the far southeast as the upper system and
surface low depart. The nocturnal range form tonight into Sunday
night will be very limited by cloud cover with Sunday highs near
10 degrees below normal.

.LONG TERM...(Monday through Saturday)
Issued at 335 PM EDT SAT APR 22 2017

Models are in decent agreement through the extended with mid/upper
level flow. In general, the southern Appalachian region will fall
under the influence of mean southwesterly flow aloft. That would
indicate warmer weather than not, and an occasional shot at showers
and thunderstorms should any disturbances in the mean flow get close
enough to affect our area. One such disturbance does appear to skirt
just close enough to provide a chance of showers Wednesday night
into Thursday. Forecast soundings suggest instability is lacking but
considering the time of year, will maintain inherited Isold thunder
for this time frame. When compared to the ECMWF and Canadian, the
GFS is somewhat of an outlier towards the end of the extended window
with the potential of a second disturbance. The ECMWF and Canadian
swing this second disturbance through the area by late Friday into
Saturday, though the ECMWF is much more subtle with this feature.
Once again forecast soundings indicate instability is lacking, but
considering the synoptic pattern feel it would be prudent to
maintain at least a slight chance of thunder.

Sensible weather will seem closer to a summer like pattern than
spring with temperatures averaging some 5 to 10 degrees above
normal. Temperatures warm nicely through the week, with highs
climbing into the lower to mid 80s for much of the week. Lows fall
generally in the upper 50s to lower 60s each night. Outside of the
two disturbances mentioned earlier, any chance for rainfall would be
quite low based on soundings as a substantial cap appears to be in
place for most of the period.

&&

.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.

&&

$$

SHORT TERM...JP
LONG TERM...RAY
AVIATION...JP


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