Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 230835
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
335 AM CDT Tue May 23 2017

.SHORT TERM...(Today through Thursday night)
Issued at 335 AM CDT Tue May 23 2017

A period of unsettled weather will occur over the next few days
as a deep 500 mb trough develops over our region and then moves
east. Despite the impressive look to the 500 mb system, there does
not appear to be much (if any) potential of severe weather or
heavy rainfall in our area.

Today and tonight, a weak 500 mb closed low over the upper
Mississippi Valley will strengthen and drop almost due southward.
The associated surface cold front will swing east across southern
Illinois and southeast Missouri late this afternoon and early
this evening. In advance of the front, a weak southerly wind
combined with daytime heating will result in modest surface-based
instability. Showers and isolated thunderstorms will form along
the front. As the front continues east across west KY and sw
Indiana this evening, showers are forecast to increase in
coverage as the strengthening upper low approaches. The thunder
potential should diminish overnight as post-frontal northwest
winds cool the boundary layer.

On Wednesday, a rather deep 500 mb closed low will drift south
into southern IL or southeast MO by evening. Very cold temps aloft
(around minus 20 at 500 mb) will contribute to scattered showers
and even a few thunderstorms. Despite the cold air aloft,
surface-based capes are forecast to remain mainly below 500 j/kg
in the cool northwest surface flow. This weak instability may be
sufficient for isolated thunderstorms with small hail, especially
if any breaks of sun contribute to stronger surface heating. High
temps will be only in the 60`s.

Scattered convection will diminish with loss of daytime heating on
Wednesday night. There will be some partial clearing in southeast
MO and southwest KY overnight. Overnight lows will be in the lower
50`s.

On Thursday, a band of rain or rain showers is depicted by the 00z
models in a deformation zone on the west side of the departing
500 mb low. This deformation zone is likely to be over southwest
IN and the Pennyrile region of west KY in the morning. Clouds may
take much of the day to exit southwest IN and the Pennyrile
region, where highs will struggle to reach the upper 60`s.
Elsewhere, the models continue to indicate enough clearing for
temps to reach the lower or mid 70`s. Thursday night will be
mainly clear with lows in the 50`s.

.LONG TERM...(Friday through Monday)
Issued at 335 AM CDT Tue May 23 2017

Forecast confidence is moderate throughout the extended portion of
this forecast.

The primary feature throughout the extended portion of this forecast
will be a large upper-level low pressure system initially over south
central Canada. The GFS pushes this system southward into the
northern Plains/Upper Midwest by Sunday and then eastward toward
southern Ontario by Monday evening. The ECMWF just wobbles the
system slowly eastward into Ontario by Sunday.

We will have south winds to begin with Friday, and low-level
moisture will be on the increase , with surface dewpoints expected
to climb into the 60s during the day. Friday is still expected to be
dry except perhaps on the western or northern periphery of the
region. The ECMWF and GFS both develop warm advection convection
over our region Friday night, but the coverage is debatable, with
the warm front already to our north.

As a major impulse rotates around the base of the upper trough,
convection will be focused on or just ahead of the associated cold
front that the ECWMF moves through our region late Saturday night
into early Sunday. The ECMWF then dries us out for Sunday through
Monday night.

With its upper system farther south, the GFS is slower to bring the
cold front through the region, and keeps our area wetter through
Sunday and even into Sunday night in the east. It does keep Monday
dry over most of the area, but it brings another impulse southeast
around the departing upper low that will result in more convection
mainly across northern portions of the area Monday through next
Tuesday. The ECMWF has a much weaker impulse that may force a few
showers or storms near a weak cold front that would move through
eastern portions of the region late Monday night into next Tuesday.

This forecast will have mainly chance PoPs from Friday night through
Sunday evening, and then there will only be slight chances mainly
over our northern counties Monday afternoon through next Tuesday
evening. Temperatures will start out near normal for highs and above
normal for lows, and then cool a category or so for Sunday through
Tuesday.

All things considered it looks like Memorial Day will be the pick
day of the holiday weekend.

&&

.AVIATION...
Issued at 1205 AM CDT Tue May 23 2017

Widespread mid and high clouds in the 10 to 15k foot range will
continue through Tuesday. Some of the light rain in Tennessee during
the early morning hours could arrive as virga in west KY, but the
mid levels are too dry for this to reach the ground. Winds will be
light. Tuesday evening, a cold front will cross se Missouri,
accompanied by some light showers. An isolated thunderstorm is
possible, but odds are too low to mention in tafs. Significant
changes in wind and cigs are expected just beyond this taf period.

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

$$

SHORT TERM...MY
LONG TERM...DRS
AVIATION...MY



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