Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 220902
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
402 AM CDT Mon May 22 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 316 AM CDT Mon May 22 2017

A very pleasant and comfortable day is in store as surface high
pressure drifts overhead. Passing high clouds may filter the sun
at times, so overall sunshine may be limited. The next system will
be waiting in the wings as an upper low pressure system digs south
into the Plains tonight/Tuesday. This system will probably not
affect much of our region until later in the day Tuesday, and esp
Tuesday night when the upper trof moves farther southeast toward
the MS River Valley and spawns a weak surface low over the
region.

Low level moisture return looks to be meager at first, but
increasing mid/upper level forcing/ascent should lead to a fairly
extensive area of scattered showers, possibly even isolated
rumbles of thunder, Tues night/Wednesday AM. The upper low will
continue to deepen near the MS River Valley Wednesday, keeping
shower chances on the high side. Would not be surprised if we end
up with some isolated thunderstorms underneath the upper low,
where mid level lapse rates could be fairly steep. If deeper
convection does manage to form, cold temps aloft could lead to
some small hail at the surface.

.LONG TERM...(Thursday through Sunday)
Issued at 316 AM CDT Mon May 22 2017

The main forecast issue is the holiday weekend outlook, which looks
rather warm and wet at this point. Although a washout is not
expected, the odds of at least one organized convective complex look
pretty high.

Prior to the weekend forecast, a strong upper-level trough will be
exiting our region on Thursday. The models have trended just a
little slower with this system. The 500 mb system will likely still
be centered over central Kentucky at 12z Thursday. A small chance of
morning showers will be forecast for the Pennyrile region of west KY
and southwest IN. The clearing trend will be slower in that same
area. Corresponding with the sharp moisture gradient, there will be
a sharp gradient in temps. Highs will range from the 60`s in sw
Indiana to the mid 70`s in se Missouri.

On Friday, a 500 mb shortwave ridge will move across our region
between systems. The models forecast strong warm/moist advection at
850 mb, which should generate some clouds. However, the measurable
precip is kept just north and west of our region through Friday.
Highs will be in the lower 80`s.

Friday night into Saturday, moisture will continue to stream
northeast across our region ahead of a cold front. Surface dew
points will climb into the upper 60`s on Saturday. The models bring
the cold front southeast into northern/western Missouri on Saturday.
Consistent with our late spring climatology, conditions will be
prime for mesoscale convective system (mcs) activity. Convective
systems would likely propagate east to southeastward through the
moist and unstable air mass over our region, as indicated by Corfidi
vectors and model qpf guidance. Since the timing of such systems is
dependent on mesoscale features with low predictability, pops for
any specific 6-hour window will be no higher than 50 percent. The
predictability of severe weather and heavy rain potential is also
limited by mesoscale uncertainties. The 00z GFS instability and
shear parameters are quite favorable for organized severe wx,
however 00z ecmwf cape values are considerably lower.

Model agreement lowers on Sunday, when the 00z ecmwf becomes much
faster than the gfs/gefs mean with the cold front timing. The
forecast model blend splits the difference. Based on the blend, the
front would come through during the afternoon Sunday. Therefore,
little change in the weather is forecast through the weekend.

&&

.AVIATION...
Issued at 1159 PM CDT Sun May 21 2017

VFR conditions to remain through forecast period. Only minor
tweaks made to reflect mean wind changes through Monday.


&&

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

$$

SHORT TERM...GM
LONG TERM...MY
AVIATION...Smith



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