Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 152055
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
255 PM CST Mon Dec 15 2014

.SHORT TERM...(Tonight through Thursday)
Issued at 235 PM CST MON DEC 15 2014

In the near term, the band of showers that has marched thru most
of the FA produced generally 1/4 to 1/2 inch amounts, and will
move on out of the far eastern counties late this pm/early this
evening. The cold front is not far behind, approaching the western
reaches of the FA at this writing, and will be marching thru the
FA this evening/overnight. As it does, the parent cyclone rotates
eastward across the MS valley, and draws down additional/low level
cloudiness to reinforce any potential evening dry slotted breaks.
In other words, despite the chance for some short-lived breaks, we
think the overnight will be generally cloudy with possibly even
some additional spits of rain/sprinkles/drizzle at times.

With the Low`s movement east across the Wabash river valley tmrw,
it will eventually be far enough east to start seeing some breaks
in cloud cover in SEMO by late pm, and this should spread eastward
into tmrw night as the Low departs further thence.

A more or less zonal flow develops then, for about a 12-24 hr
period prior to our next developing Low pressure system. It
develops in response to long wave troffing in the Southwest, that
ultimately shoots moisture/pcpn quickly out of the southern Plains
and into our FA Wed night. The models track the bulk of the
moisture across the lower MS valley and to our south, but do lend
the northern extent of QPF across our southern 2/3 counties. The
airmass it encounters is marginal for rain/snow, with model qpf
ranging from a few hundredths to a mid teens tenth of an inch.
Where qpf is best (south), temps are warmer, and suggest rain.
While we think this will mean all rain for our southern counties,
the collab pic suggests an either/or wording should carry for now
on this chance category, light pcpn event.

We could have carried a scant slgt chance 20 pop on our cwa
border/periphery, and may yet depending upon the collab pic, but
view it as generally unnecessary as the system`s moisture has
generally departed by then.

.LONG TERM...(Thursday night through Monday)
Issued at 235 PM CST MON DEC 15 2014

The main concern in the long term still continues to be the storm
system for Friday into Saturday. There has been little change in the
models, which have been split into two camps for the past few days.

The first camp is the gfs and gfs ensemble mean, both of which
remain weaker and further north with the system. The most recent
gfs runs are notably weaker than previous runs. There is no apparent
closed circulation at any level in the most recent 12z gfs. This has
resulted in lower qpf, generally about one-third inch (storm total)
in western Kentucky with less to the north. The gfs and its ensemble
mean are still relatively warm, indicating mainly a rain event for
most or all of the forecast area.

The second camp is the ecmwf and its ensemble mean, both of which
are further south. The ecmwf had been stronger with the system, but
the most recent 12z run is considerably weaker than previous runs.
This results in much lower qpf than its previous runs, generally
about one-quarter inch of liquid equivalent in the southeast
counties (less to the north). The further south solution allows
colder air to get drawn into the region, which implies snow or a
changeover to snow for most of the forecast area.

The WPC medium-range forecasters have been favoring the ecmwf camp,
partly due to its agreement with the experimental high-resolution
13-kilometer gfs. The forecast will lean toward the colder ecmwf,
but there are a couple of concerns with it. Despite its further
south storm track, the ecmwf has trended warmer in our area than 24
hours ago. The 06z 13-km parallel gfs, which matched the ecmwf storm
track closely from the surface to 500 mb, was warmer than the ecmwf.
The 06z parallel gfs kept surface and 850 mb temps above freezing
through the event, implying all rain.

The second concern with the ecmwf is the lack of consistency with
regard to the strength of the system, as shown by the flip-flop
between 00z and 12z today. The event is still several days away,
which is too early to expect close agreement from the models. The
forecast will generally stay similar to the previous one, keeping
precip as either rain or snow. The highest pops will be Friday
night, when most of the models agree the system will be closest. The
gfs is still faster, ending the precip late at night, while the
slower ecmwf starts it at night.

Outside of the aforementioned system, there is not much in the way
of precipitation in the forecast. Temps will generally be around 40
in the day and 20s at night outside of the storm system.

&&

.AVIATION...
Issued at 235 PM CST MON DEC 15 2014

Warm sectored IFR cigs wil prevail early, behind main band of
showers departing KEVV/KOWB at this writing. Then overnight, cigs
should alternate between that and MVFR as front makes passage and
parent cyclone rotates across MS river valley. Notwithstanding a
few breaks otherwise, it will be generally cloudy and some light
showers, sprinkles, or light drizzle may mist with fog and create
some MVFR vsbys at times. Otherwise expect winds shifting to west
or northwest. Cyclone should continue eastward progress tmrw
across the Wabash river valley, with hint toward improving cigs
the further it moves away.

&&

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

$$







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