Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 261148

Area Forecast Discussion
National Weather Service Paducah KY
648 AM CDT Wed Apr 26 2017

Issued at 648 AM CDT Wed Apr 26 2017

Updated aviation discussion for 12Z TAFs.


.SHORT TERM...(Today through Thursday night)
Issued at 330 AM CDT Wed Apr 26 2017

Main near term forecast concern continues to be the potential for
thunderstorms through tonight and accompanying severe weather
potential late this afternoon into this evening. Forecast confidence
remains relatively high through Thursday night with generally good
overall model agreement.

Shortwave energy digging into the base of an upper level trough over
the southern Plains this morning will take on a negative tilt as it
pivots northeast across the Middle Mississippi Valley tonight. The
approach and passage of this shortwave and its associated cold
frontal boundary will provide the focus for shower and thunderstorm
development later this afternoon and this evening. Model forecast
soundings continue to indicate the presence of a strong mid level
capping inversion through much of the daytime hours today. As a
result, it will take the strong forcing of the incoming cold front
to result in the development of surface-based convection by mid to
late afternoon. Any activity that occurs prior would likely be tied
to the elevated mixing layer and should not pose a severe threat.

All ingredients for severe storm potential appear to be available
later this afternoon into this evening except for perhaps one key
factor--instability. The presence of low level moisture in forecast
soundings suggests that much of the enhanced and slight risk areas
locally should see a good deal of cloud cover throughout the day.
Consequently, even once storms enter southeast Missouri by mid to
late afternoon, they may only have a modest amount of instability to
work with. Strong dynamics may initially overcome this shortcoming.
However, as the storms move east and instability decreases during
the evening, they should begin to weaken fairly quickly. Should more
sunshine break through the cloud cover, then instability would
likely be appreciably higher, in addition to severe potential.

At this time, the greatest risk for severe weather still appears to
be in southeast Missouri, where linear bowing segments and possibly
a few embedded supercell structures should be the favored storm
mode. Damaging winds remain the primary concern, while large hail
and a brief tornado cannot be ruled out, especially early on. Storms
should begin to weaken as they progress across southern Illinois and
far western Kentucky during the early evening hours. A line of
storms will likely progress into southwest Indiana and east of the
Land Between the Lakes in Kentucky by late evening, but activity by
then should largely be sub-severe.

Any lingering showers should taper off late tonight and early
Thursday morning as the storm system departs to the east. Much of
Thursday should be dry, albeit cooler in the wake of the front.
After highs in the upper 60s (west) to lower 80s (east) today, highs
on Thursday should remain in the 60s. The next chance of showers
should hold off until late Thursday night at the earliest as the
front begins to return north as a warm front ahead of low pressure
over the Plains.

.LONG TERM...(Friday through Tuesday)
Issued at 330 AM CDT Wed Apr 26 2017

Confidence remains fairly high that an unsettled weather pattern
that will be with us Friday night and again Saturday night/Sunday.
Less confidence in the exact timing and location of where the
heaviest rainfall will occur.

An upper level ridge of high pressure will build over the southeast
U.S. into this weekend, while an upper level trough digs into the
southern Rockies. This trough will eject east into the Southern
Plains on Sunday before lifting northeast into the Great Lakes on
Monday. The Quad State will be within deep southwesterly flow Friday
through Sunday. Right now Friday night and Saturday night/Sunday
look to have the highest heavy rainfall and severe storm risks.

A warm front will develop northward by Friday evening from the
southern OH/TN valleys southeast into northern TX or southern OK.
The best chance for more widespread thunderstorm initiation will
occur during the evening into the overnight hours along and north of
the warm front as strengthening, broad low-level jet enhances
convergence and lift along and north of this boundary. Strong
vertical shear profiles and steep mid lvl lapse rates will support
organized storms including supercells with large hail and damaging
wind the main threats, though a few tornadoes may also occur with
surface-based storms developing closer to the warm front.

It looks like the warm front will lift to the north of the region
Saturday as the upper level high pressure system off the Southeast
Coast tries to build back to the west toward the region.  This could
bring a general break in the shower/thunderstorm activity,
especially over western KY/far srn IL/sw IN. Depending how far north
the warm front gets Sat, will decide whether more of the area ends
up dry during the day.

However, shower/storm chances will ramp back up Saturday night into
Sunday as the main upper trough and associated cold front approach
from the west. Model guidance has been consistent in placing the
heaviest QPF over southeast Missouri into southwest Illinois
Saturday night, but central and eastern portions of the forecast
area should get into the act Sunday. Overall rainfall amounts Friday
through Sunday in the 3 to 5 inch range will be possible from
southeast MO into IL, with locally higher amounts not out of the
question. Somewhat lighter amounts are expected as one heads farther
east into wrn KY/sw IN. Given the very strong dynamical forcing
expected with the main upper trof, severe storms will also be a
possibility later Sat night into Sun. Much of the severe threat will
depend on how much instability can form ahead of the sfc front.

The cold front and associated precipitation should be lifting out of
the area by late Sunday night into Monday morning. Dry conditions
are expected Monday and Tuesday, along somewhat cooler conditions
initially on Monday. Should be back in the 70s to near 80 by Tue/Wed
time frames.


Issued at 648 AM CDT Wed Apr 26 2017

As low level moisture spreads into the area ahead of a weather
system approaching from the Plains, low VFR ceilings should develop
across much of the area today. A period of MVFR ceilings is possible
from mid morning through early afternoon, especially across portions
of southern Illinois and southeast Missouri. A line of thunderstorms
is forecast to accompany an eastward advancing cold front late this
afternoon into tonight. Strong to severe thunderstorms are possible
early on--especially along and west of the Mississippi River. Storms
will also bring strong gusty winds in addition to reduced ceilings
and visibilities to MVFR or perhaps IFR levels. South winds will
average 10 to 15 knots with occasional gusts to 25 knots ahead of
the front. Behind the front, winds will shift to the west/southwest
as ceilings improve to 2500-3500 ft.




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