Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 191935
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
235 PM CDT Thu Jul 19 2018

.SHORT TERM...(Tonight through Saturday night)
Issued at 232 PM CDT Thu Jul 19 2018

Main concern is severe weather potential late this afternoon and
evening, and moreso on Friday/Friday evening. Anomalously strong
winds aloft coupled with high instability could lead to some very
active weather Friday.

In the near term, a convective complex over central Missouri will
continue tracking south/southeast along a gradient of moisture and
instability, basically the remnants of a surface frontal zone.
The complex will be tracking across the Ozark foothills during
peak heating and instability late this afternoon. Given moderately
strong instability with mlcapes near 2000, marginal deep layer
shear will be sufficient for damaging wind and hail potential in
the slight risk area over se Missouri. The high-res cam models
suggest some additional weaker development may take place on the
eastern flank of the mcs, extending as far east as southern IL and
far west KY this evening.

During the overnight hours, there is considerable variability
among the models. It appears some elevated convection could occur
in response to the closed 500 mb low sliding east-southeast into
the Great Lakes region. The presence of fairly strong surface-
based capping should limit any severe wx potential to isolated
large hail. The potential for an elevated mcs will continue into
the morning hours on Friday. The high-res cam models seem to lean
toward sw Indiana and adjacent areas of IL/KY for the location of
an elevated mcs.

On Friday, the potential for a significant severe weather outbreak
exists due to the anomalously strong mid and upper level flow,
coupled with tropical dew points and strong instability. The
location and timing of convection is complicated by a number of
factors. First, there will be a capping inversion in place.
If widespread convection occurs in the morning, it will take
longer for surface heating to break the cap. In fact, there is
some possibility the cap will not break west of the Mississippi
River, where convective inhibition at peak heating is forecast to
be around 50 j/kg on the 12z nam. Elsewhere, it appears the cap
strength will be nearly ideal for holding back convective
initiation until peak heating/instability. In the presence of any
outflow boundaries, explosive development is possible with
mlcapes from 2500 to 4000 j/kg. However, the exact source of
initiation is not clear at this time.

Deep layer bulk shear will be around 40 to 50 kt in the afternoon,
increasing to around 60 kt in the evening. This is very favorable
for rotating supercells. Low level flow will be fairly weak,
averaging 10 to 15 kt at and below 850 mb. This may be a bit of a
limiting factor for tornadoes, however the overall environment
appears conducive for at least a couple tornadoes with discrete
cells. Large hail and damaging winds will be distinct threats as
well, given the high forecast downdraft capes locally over 1500
j/kg.

Activity will diminish Saturday night with loss of heating and the
overturning of the atmosphere by afternoon/evening convection.

.LONG TERM...(Saturday through Thursday)
Issued at 232 PM CDT Thu Jul 19 2018

High confidence that an upper level low/troughing will influence our
weather for a good majority of the extended period. Also high
confidence of near to below normal temperatures this weekend through
much, if not all, of next week.

The period starts out with an upper level low centered over IN/OH
this weekend. This feature looks to slowly dive south/southwestward
and weaken early next week, centering itself near the Gulf Coast
states by Tues/Wed timeframe. By this time, shortwave troughing is
forecast to be working into the upper Midwest. Ahead of this, a
brief period of ridging is forecast to try to nudge into the region
from the west. Afterwards, ensemble guidance has been in decent
agreement developing troughing over our region later in the work
week.

Overall, PoP chances exist over at least some portion of the region
nearly every day through the extended. The best chance this weekend
looks to be on Sunday, as a surface trough progresses through the
region associated with a surface low pivoting southward in the
Louisville area. There appears to be enough instability around for
daily thunderstorm chances, especially during the peak heating
hours. However, no severe weather is anticipated in the extended at
this time. Mainly diurnal showers and thunderstorms will tend to
continue into at least Tuesday, possibly even Wednesday, as our area
remains under the influence of the upper low. Surface flow will
predominately contain some northerly component through the period.

High temperatures will primarily range from the mid 80s to near 90
most days. However, with increased cloud cover and precipitation
chances on Sunday, highs may struggle to reach 80 in southwest
Indiana and the Pennryrile of west KY. This very well may be the
coolest day much of our region has experienced since June 22nd!
Temperatures will tend to moderate closer to normal around 90 by
Tues/Wed. However, after what we have endured much of the summer so
far, this weekend into next week will feel rather refreshing in
comparison.

&&

.AVIATION...
Issued at 1225 PM CDT Thu Jul 19 2018

VFR conditions will continue through this evening east of the
Mississippi River. A thunderstorm complex over central Missouri at
noon will track south-southeast. The eastern flank of this complex
could reach the kcgi taf vicinity late this afternoon and continue
early this evening. Another thunderstorm complex is possible late
tonight or early Friday. The path of this complex appears more
likely to be in the kevv/kowb area, where vcts will be included in
the tafs. Winds will be southeast 5 to 10 knots today, becoming
south tonight and southwest on Friday morning.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

SHORT TERM...MY
LONG TERM...SP
AVIATION...MY


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