Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 170828
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
328 AM CDT Thu Aug 17 2017

.SHORT TERM...(Today through Saturday night)
Issued at 328 AM CDT Thu Aug 17 2017

Band of convection forecast to move across the area from west to
east through the day, departing our east counties this evening.
Will use likely category PoPs early this a.m. into SEMO, southern
IL, then scattered terminology with isolated storms rest of the
time, given the trend around here lately is for convection overall
to be somewhat underwhelming. Will monitor for a couple of
stronger storm events. Right now, parameters not looking too
favorable though. There is some modest MLCAPE forecast. But
1000-850mb lapse rates, and DCAPE values are marginal. Mid level
lapse rates are not impressive, and thermal profiles suggests hail
threat minimal to none. Dry after midnight tonight, and on
through Friday and Friday night with weak high pressure moving
across the area. Saturday, kept PoPs slight chance for convection,
as energy aloft moves across the area from NW to SE. Dry Saturday
night, though may have to monitor southern sections in the
evening for a slight chance.

.LONG TERM...(Sunday through Wednesday)
Issued at 328 AM CDT Thu Aug 17 2017

From the regionally blended model initialization, some of the
emphasis of the PoPs seems to reflect the influence of the Canadian,
more so than the GFS/GFS Ensemble and European (ECMWF).

The retrograding west to east oriented high pressure over the
southern Plains and southeastern U.S. early Friday appears to shift
east with time Sunday through Tuesday until a broad shortwave in
Canada, sharpens over the WFO PAH forecast area later on Tuesday.
This places the WFO PAH forecast area into a strong northwest flow
through the middle of the week.

At this point, only have medium confidence in PoP/Weather forecast,
mainly due to the timing, degree, and trajectory of deep layer
moisture into the WFO PAH forecast area. The Canadian is the
wettest, followed by the ECMWF, then the GFS/GFS Ensemble.

Any convective activity during the Sunday through Tuesday time
period across the WFO PAH forecast area will be diurnal in
character, with the mid-week convective activity dynamically tied to
the passage of the shortwaves in the northwest flow over the area.

...Discussion for Solar Eclipse - WFO PAH Forecast Area...

The model trends of the GFS/GFS Ensemble/ECMWF/Canadian all seem to
place the WFO PAH forecast area on the western end of the low and
middle level ridge axis, with a minor vorticity lobe moving through
Missouri around 18z (1 pm CDT) Monday. The trend suggests some form
of an MCS developing over KS and OK overnight, then moving east
through southern Missouri during the morning.  Depending on the
maturity and initiation time of the MCS, there may still be
lingering showers and a few thunderstorms Monday morning, especially
over southeast Missouri. The question will arise on how much
convection will be maintained into the early afternoon. Right now,
the current forecast package will have greater than 25% rain chances
along a line from Mayfield and Paducah Kentucky, onward to Eddyville
and Pinckneyville Illinois. Given the low PoP through the remainder
of Southeast Missouri, we may only see pockets of showers and
thunderstorms. However, given the flow, this could still spread a
measurable opaque cirrus cloud deck downstream across the rest of
the WFO PAH forecast area. With the cloud cover and precipitation
potential, kept temperatures in the middle 80s through the partial
and total eclipse time periods.

There is still quite a bit of wiggle room, especially on the
mesoscale, so forecast confidence in this scenario is 50/50 now.

&&

.AVIATION...
Issued at 328 AM CDT Thu Aug 17 2017

Will monitor convective chances, as a weak front moves across the
area, shifting SSW winds more to the west through the day and into
the early evening. Activity currently over SEMO should reach the
I-55 corridor by or shortly before daybreak. Adjusted the KCGI
forecast to include activity moving in from the west.

&&

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

$$



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