Area Forecast Discussion
Issued by NWS Paducah, KY

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378
FXUS63 KPAH 241931
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
231 PM CDT Wed May 24 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 231 PM CDT Wed May 24 2017

Despite the approach of the sharper lapse rates with the upper low ,
CAPE (per NAM BUFR Sounding data) suggest less than 250 j2/kg2
will be available for any thunderstorm development, with
equilibrium level near 13-14kft MSL. Added an isolated mention of
thunderstorms through southeast Missouri and extreme southwest
Kentucky for the remainder of the afternoon, but may need to
remove it earlier, if nothing occurs within the next 1-2 hours.

The NAM-WRF model suite appears to have a generally good handle on
the evolution and transformation of the closed low moving south
through into the Lower Mississippi Valley and the generation of a
secondary low in southern Indiana this evening overnight. This
will support more sustained convection over southwest Indiana and
northwest Kentucky this evening and overnight.

Any remaining convection in the WFO PAH forecast area should
recede quickly to the east as a deep shortwave ridge builds into
the area from the west late tonight into early Thursday and
Thursday night.

The short and medium range guidance suggests a minor shortwave
dampening the ridge over Kansas/Missouri/southeast Nebraska late
Thursday night. There is lower confidence on the evolution of
convection and marginal severe potential for Friday (suggested by
SPC Day 3 Outlook) at this time, as models vary on the intensity
of lift and moisture over the WFO PAH forecast area. For now, kept
with the initialized, region model blend guidance as a starting
point. Otherwise, there is higher confidence in the forecast from
tonight through Thursday evening.

.LONG TERM...(Saturday through Wednesday)
Issued at 231 PM CDT Wed May 24 2017

High confidence for the synoptic scale features with medium
confidence with the longevity of precipitation.

We will start Saturday with scattered storms possible with the best
chance along and west of the Mississippi River. There will still be
an elevated inversion or cap over the region Saturday but it is much
weaker over SEMO. So would expect the best chances there. However
with adequate instability with LI`s averaging around a negative 5
and CAPEs ranging from 1k-3k j/kg2 storms that do break through the
cap could be strong or even severe...especially Saturday night into
Sunday as the cold front moves through. Also the the Gulf is open
near the surface for abundant low level moisture. In the mid and
upper levels the moisture will have flow around a high centered over
the gulf. This will force the deeper moisture to flow through Mexico
and the southern plains before it can reach the area. This deeper
moisture will arrive in concert with the frontal passage. This
should saturate the column...providing a deep moisture layer for the
storms. So this could result in heavy rainfall or even some flash
flooding...being the main threat. However ample instability will
still exist for a strong or severe thunderstorm...especially western
section of the fa. We should dry out and cool down for Memorial day
or Monday. A much weaker reinforcing cold front will be poised move
through Tuesday bringing at least a slight chance of a thunderstorm.
Mitigating factors for this second front will be limited moisture
and instability. As for temperatures expect above normal
temperatures for Saturday and possibly even Sunday then cooler and
slightly below normal temperatures for the first half of next
week.

&&

.AVIATION...
Issued at 1220 PM CDT Wed May 24 2017

With this 18z Wednesday WFO PAH routine TAF package, kept IFR
ceilings and MVFR/IFR visibilities in KEVV/KOWB due to clouds and
banded rainfall rotating north ahead of a shortwave rotating east
of a closed low as it dives south into western sections of
southeast Missouri. Added a mention of vicinity showers to
KCGI/KPAH to address instability-based convection with the upper
low during peak heating.

For the late afternoon and evening improved conditions to VFR for
the WFO PAH TAF locations to reflect contraction of weather and
eastward movement of the upper low.

However, kept lower ceilings and visibilities overnight, as lift
associated with the upper low generates some drizzle at KCGI/KPAH
and IFR/MVFR ceilings at KEVV/KOWB through Thursday morning.


&&

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

$$

SHORT TERM...Smith
LONG TERM...KH
AVIATION...Smith



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