Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 220544
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
1144 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight through Tuesday night)
Issued at 228 PM CST SUN DEC 21 2014

Forecast confidence relatively good through the first half of the
short term period, then drops off somewhat toward the end due to
model timing and track differences.

A storm system developing over the northern plains will push a cold
front toward our region on Monday. Southerly flow ahead of this
system will bring a surge of deep moisture across the region
tonight. This combined with a weak short wave moving across the area
may produce enough lift to generate small precipitation chances over
our far western counties late tonight.

As the front draws ever closer on Monday, precipitation chances will
increase from west to east across the entire area. Monday night into
Tuesday morning models show a lobe of the parent H5 low
developing/digging a trough southward across the plains. This will
enhance upper support and combined with the passage of the front,
precipitation chances will increase significantly. By late Monday
night/early Tuesday morning, there may be enough surface based and
elevated instability to warrant the mention of thunder over the far
southeast sections of the CWA.

There may be a lull Tuesday afternoon in precipitation chances if we
get dry slotted in the wake of the front, but not confident enough
to reduce those POP grids at this time. For the same reason as in
the above paragraph, mentioned thunder chances over the eastern and
southeastern sections of the CWA all day Tuesday.

Tuesday night with the deepening and northeast track of the
aforementioned H5 trough, models are inducing a surface low/wave on
the front and bringing another surge of moisture and elevated
precipitation chances across the region. However, models not in good
agreement on how this will play out at this time. The GFS is clearly
the most aggressive with the development of this feature and the QPF
it generates over our area. The NAM12 and SREF not that excited
about it at all and keep almost all precipitation chances over the
southeast sections. Models still showing a sliver of instability
over the southern Pennyrile region of western Kentucky Tuesday
evening, so have a mention of thunder there.

Thanks to surrounding offices for forecast coordination.

.LONG TERM...(Wednesday through Sunday)
Issued at 228 PM CST SUN DEC 21 2014

Medium confidence in extended forecast.
The ECMWF has much better run to run continuity and the most best
continuity among other models ensembles. The GFS has the greatest
run to run variability and would be most likely the odd one out.

At the start of the extended or Christmas Eve...a broad upper level
wave exiting the plains and moving toward the Mississippi Valley.
Models are good general agreement with this feature. They do differ
a great deal with the placement and movement of a developing surface
low along the front over KY while the parent low moves through LM.
Most of the operational models and ensembles bring the surface low
up through eastern KY. The GFS however is slightly more west of the
aforementioned models and tracks the surface low through central KY.
Regardless of which solution they all agree that surface temps will
be too warm for much of wintry weather. However forecast sounding
and Bufkit suggest a possible mix as the moisture exits the area.
Considering this out to day 4 dont want to box myself in or create a
possible flip flop in the forecast will probably go with a chance of
a mix in case moisture lingers longer or the cold air arrives faster.
The colder air is not here at least until the afternoon so will hold
off any chance of a mix until then.

The nest system arrives Friday with a vertically stacked low moving
through the great lakes region with a cold front extending southward
through the forecast area into the gulf by 18z Friday. This system
will be moisture starved and warm for this time of year. Yet once
again we could rain mix or changeover to snow before ending Friday
night. Once again little impact expected with this system.

As for temps went mostly above normal through the period and there
was slight increase on a few days from previous run.

&&

.AVIATION...
Issued at 1144 PM CST SUN DEC 21 2014

Was too pessimistic with the onset of MVFR/IFR ceilings with the
00z Monday TAF issuance. Significantly slowed the onset of lower
ceilings and visibilities to MVFR. Adjusted the 06z Monday TAF
issuance to reflect this change.

&&

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

$$

AVIATION...Smith





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