Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 211750
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1250 PM CDT Tue Mar 21 2017

.UPDATE...
Issued at 1250 PM CDT Tue Mar 21 2017

Updated aviation discussion for 18Z TAFs.

&&

.SHORT TERM...(Today through Thursday night)
Issued at 230 AM CDT Tue Mar 21 2017

The frontal boundary is now straddling western Ky, and the models
have had a good grasp on its placement for the last 12 hours or
so. They sag it just south of the FA by 12Z, after which,
convective chances start to initiate via warm air
overrunning/elevated instability, as the leading dynamical energy
aloft starts to spill in/overtop the boundary. This Marginal to
Slight Risk Svr activity really picks up during the pm/evening
hours, as the vort energy increases its affect with the
approaching jet streak. The activity by then may gain some surface
based instability, but the latest modeling keeping us north of
the boundary suggests the primary initial hazard is hail, with the
potential for wind damage if evolution of the cluster storm
genesis area results in mesoscale driven surface based activity.
Lightning and heavy rain, with PW`s at the 90th-95th percentile
around 1.2", will be commonplace storm associated hazards. The
overall convective feed ends north to south overnight as
drier/cooler air invades the column via the Canadian CP airmass
driven by surface High anchoring over the Great Lakes and
extending its reach southward and eastward across the Ohio river
valley. Temps well into the 60s today, with dew points nearly so
not far off, will cool close to 15F tmrw, before moderating up
again another 5-10F Thursday as the High shifts its anchor
eastward.

.LONG TERM...(Friday through Monday)
Issued at 305 AM CDT Tue Mar 21 2017

This period appears to be the start of a rather warm and wet pattern
that will extend into next week. A longwave ridge will become
established over the eastern states as the mean trough position sets
up over the western states. A series of shortwaves will eject
northeast across the Plains, bringing periods of wet weather and
warm southerly winds.

On Friday, warm-advection cloudiness will increase ahead of a storm
system over the central Plains. A tight pressure gradient will
result in strong low-level south winds. These gusty south winds will
raise dew points into the 50s, contributing to marginal instability
by later Friday night. Most of the warm advection induced precip
should hold off until the night time hours.

The highest pops will be Saturday, when a surface low center tracks
northeast across central or western Missouri into central Illinois.
The associated 500 mb system may be a rather impressive closed low,
as depicted by the 00z ecmwf. The synoptic pattern looks favorable
for strong convection, but the timing of the strongest forcing
coincides with the cooler morning hours. Even with more favorable
diurnal timing, the modest amount of low-level moisture would be a
limiting factor for convection. Temps will be dependent on timing
and coverage of precip, which is quite a challenge. The model
consensus points toward considerable clouds with highs near 70.

In the wake of the weakening shortwave, a drying trend should move
east to the Mississippi River on Sunday. The drying process may not
reach southwest Indiana or southeast Illinois due to the stalling
out of a cold front trailing southwest from the remnant low. Highs
should be mainly in the mid to upper 60s based on the expectation of
abundant clouds. However, both the 00z ecmwf and gfs mos indicate
lower to mid 70s. These values are based on a drier forecast from
these recent model runs.

The next system will follow a similar track to our west and
northwest early next week. Showers and storms may return as early as
Monday based on the 00z gfs/ecmwf and ensemble means. The supply of
moisture and instability may be more substantial, but this is still
subject to model changes seven days out. Forecast highs are several
degrees cooler than mos guidance for Monday, and this again seems to
be related to differences in moisture/clouds/precip.

&&

.AVIATION...
Issued at 1250 PM CDT Tue Mar 21 2017

Shortwave energy rippling along and north of a stalled frontal
boundary over Arkansas and Tennessee will bring a period or two of
showers and thunderstorms to southern portions of the region this
afternoon, with lingering showers possible this evening. This will
impact primarily the KCGI and KPAH forecast terminals. While brief
reductions to MVFR conditions cannot be ruled out in association
with thunderstorm activity, main VFR conditions are expected through
the forecast period with mid and high level cloudiness. Northeast
winds around 10 knots will prevail.

&&

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

$$

AVIATION...RJP



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