Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 212320 AAA

Area Forecast Discussion...UPDATED
National Weather Service Paducah KY
620 PM CDT Fri Oct 21 2016

Issued at 620 PM CDT Fri Oct 21 2016

Updated the AVIATION discussion for the 00Z TAF issuance.


.SHORT TERM...(Tonight through Sunday night)
Issued at 223 PM CDT Fri Oct 21 2016

Surface pressure gradient relaxes across Southeast Missouri during
the evening and over Southern Illinois and Purchase Area of West
Kentucky, eastward to the Land Between the Lakes after midnight
tonight. Between 09z-12z, the WFO PAH CWA will be in the most
optimal range for stable boundary layer stratification, wind
decoupling, etc.  Frost development is expected, but the intensity
of the frost is questionable given antecedent insolation,
evaporation, coverage of surface dewpoint depressions less than

If temperatures in the forecast area were to be well into the middle
30s for 2-4 hours, may have revisited an advisory, but at this time,
do not expect this to be an issue, with the possible exception of
county areas north of Interstate 64. Current Special Weather
Statement in effect addresses the specifics of frost development in
the WFO PAH forecast area tonight.

Otherwise, a gradually eastward shift in the surface high pressure
ridge on Saturday into Sunday, as the westerly tilted upper level
ridge broadens during the same time period. An increase in
thicknesses and a return to a more southerly wind component should
mitigate any return to temperatures Saturday night or Sunday night.

Dry and near seasonable temperatures will be the rule through the
short term forecast period.

.LONG TERM...(Monday through Friday)
Issued at 223 PM CDT Fri Oct 21 2016

Confidence in the extended portion of the forecast is moderate.

We will start out with a fairly amplified trough/ridge/trough pattern
aloft. The ridge will be centered over the Plains states with
troughs off the west coast and over New England. As a portion of the
east Pacific trough shears out and tops the ridge, the ridge will
effectively retrograde and become centered over the southern Rockies
and southwest. This will allow the disturbance to amplify as it
reaches our region Wednesday.

The 12Z models continue to show quite a variety of solutions for
this amplification, with the ECMWF and GFS showing a closed low over
Wisconsin with a split flow scenario. Unfortunately, they are about
12 hours apart in doing so. The CMC really digs a portion of this
energy into the southern Plains Wednesday and has a much weaker
trough moving east through the Lakes into the Ohio Valley Wednesday

Prefer the CMC, where we may be stuck between the forcing with the
northern portion of the system, and the moisture being gobbled up by
the southern Plains/Arklatex system. Even if the GFS/ECMWF are
correct, moisture return ahead of it will be very meager in our
region, and figure it will be a light QPF event. The forecast has
trended a bit drier, but will maintain a mention of thunder, as the
models at least have a little bit of elevated instability, and even
surface-based instability at times.

The GFS is still trying to bring another upper-level storm system
and cold front into the region Friday afternoon and night. The ECMWF
is now dry, so there is quite a bit of disagreement here, too. Will
leave a slight chance in the northwest for Friday in case the GFS is
on to something. There will be enough elevated instability if the
GFS scenario is correct to support TS in the forecast.

Temperatures will generally remain at or above normal through the


Issued at 620 PM CDT Fri Oct 21 2016

High pressure over the region should provide VFR conditions for
all TAF sites through the period. Northwest winds AOB 5-6 knots
early will go calm overnight, then pick up out of the southwest
to west after 15Z AOB 5 knots.




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