Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 280530

Area Forecast Discussion
National Weather Service Paducah KY
1230 AM CDT Fri Jul 28 2017

Issued at 716 PM CDT Thu Jul 27 2017

There remains minor shear, moderate surface based CAPE, little
CIN, weak surface convergence (between the approaching cold front
to the north and departing MCV/effective outflow boundaries over
the southern Kentucky Pennyrile region of west Kentucky) across
the WFO PAH forecast area.

Given the weak shear aloft, the cirrus canopy from the morning and
afternoon convection limited effective heating of surface parcels
to support widespread convection. Where there was differential
heating, updrafts remained weak, making most storms outflow
dominated. In the absence of persistent upshear flow (except with
the interaction of the MCV with outflow boundaries), any potential
for multi-cell thunderstorm development was mitigated.

Cannot rule out some focused convection with the cold frontal
boundary, but had to consider a significant reduction in the
overall PoP/Weather picture for tonight, especially between the
front and the departing MCV this evening. Adjusted the
differential mention of thunderstorms to be tied with the
departing MCV in the southern Pennyrile of west Kentucky and over
with the cold front, mainly over southwest Indiana, southeast
Illinois, and northwest Kentucky.

The high resolution, convection allowing, HRRR model family, as
well as the NAM-WRF family suite was used to reflect rain chances,
rainfall amounts, weather type, and cloud cover for tonight. There
is some concern that the difluent northwest flow aloft may
tighten up Friday morning, keeping a small chance for convection
over the southern part of the WFO PAH forecast area in place early
Friday, but will need to see how the shortwave/low over Lake
Michigan will react later tonight to determine whether it will be
worth dropping any additional rainfall mention on Friday.


.SHORT TERM...(Tonight through Saturday night)
Issued at 249 PM CDT Thu Jul 27 2017

A cold front over central Missouri and central Illinois this
afternoon is heading southeast. This front will bring much quieter
and drier weather by the weekend. In the meantime, there will be
some potentially strong convection to deal with.

As of mid-afternoon, scattered storms were developing across the
Lower Ohio Valley. These storms were developing on the northern
edge of a pool of very moist and unstable air that was unaffected
by the early morning mcs that tracked across Illinois. These
storms were supported by a mesoscale vorticity center over south
central Missouri, which was evident in radar loops. This vort
center was generated by an early morning mcs over western

In the near term, convection will likely expand in coverage across
the very unstable air over western Kentucky and extreme se
Missouri late this afternoon. Once the atmosphere is raked over
and the vort center passes to our southeast this evening, there
should be relatively little activity on radar. A second smaller
round of storms is likely late tonight along the actual cold front
as it moves southeast across the Ohio River and southeast

Heavy rain appears to be the primary hazard given high precip
water values over two inches. There is also some potential for
training cells if an organized mcs develops. Corfidi vectors
indicate a slow southward motion to any organized mcs that forms.
Individual cell motion is mostly to the east.

Once the front exits the Pennyrile region of western Kentucky
Friday morning, there will be a slow drying trend during the
afternoon. Some isolated weak convection could lag behind the
front as a strong 500 mb shortwave drops south-southeast across
the Great Lakes region. The drier air will be slow to filter south
initially, which means dew points will still be mostly in the 70s.
However, clouds should keep high temps mostly in the mid 80s.

Saturday and Saturday night will be noticeably cooler and drier.
Little if any cloudiness is expected. Model soundings indicate any
diurnal cumulus clouds would be scattered at most. Even with full
sun on Saturday, highs will range from 80 to 84 with a north
breeze. Overnight lows will be in the upper 50s and lower 60s
Saturday night, which will be the coolest night since June 28.

.LONG TERM...(Sunday through Thursday)
Issued at 249 PM CDT Thu Jul 27 2017

The overall forecast confidence is high.

The dominant feature on the weather map throughout the extended
forecast will be a strong upper-level ridge over the western half of
the country. This will result in troughing of some amplitude over
the eastern half, including our region. At the surface, cool, dry
high pressure will remain in place through much of the period. The
airmass will slowly moderate, but south winds never really get
established, so the moderating process will be slow.

The medium range models bring an upper-level storm system southeast
through the Great Lakes or Northeast on Thursday, which could push a
cold front into our region. Depending on the strength/path of this
system, some convection may reach our eastern counties Thursday


Issued at 1230 AM CDT Fri Jul 28 2017

From the 00z to 06z Friday WFO PAH TAF issuance, raised ceilings
and visibilities over KCGI, but lowered initial visibilities and
ceilings in the vicinity of current convection over the KEVV and
eventually the KOWB TAF locations. The HRRR model guidance appears
to have a good handle on this scenario and the forecast was
adjusted to reflect this short term weather impact. There still
remains some uncertainty as to whether the KPAH ceilings and
visibilities will fall into the MVFR category around 12z, but will
not amend this trend at this time. Otherwise, a return to VFR
category should occur after 15z Friday and persist through the
remainder of the forecast period.




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