Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 170937
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
337 AM CST Wed Dec 17 2014

.SHORT TERM...(Today through Friday)
Issued at 330 AM CST WED DEC 17 2014

Still not very high on the confidence scale with the system
coming in for tonight and Thu AM. The overall synoptic pattern
seems fairly clear cut, but there is still quite a bit of
variance between operational model solutions concerning the
details of qpf, and to a less extent now, thermal profiles.
Confidence is increasing, however, that this should not be a major
impacting event.

A shearing/weakening H50 short wave will eject ene from the Plains
into the mid MS River Valley overnight and early Thu. This should
create a modest over running situation over a fairly cold dome of
high pressure at the surface. Light precipitation should begin to
break out over the srn Plains this morning, then gradually spread
ne toward the MS River this evening. However, the combination of a
very dry low level regime, and the fact that the wave should be
weakening with time, will likely limit the n/e progression of precip
during the night. Therefore, it looks like the highest chc of
getting a high POP/low qpf event will be confined to portions of
SEMO, the Purchase region of western KY and the southern tip of
IL.

Precip type is also problematic at this time, esp over the southern
third of the forecast area where light precip chcs will be the
highest. Forecast thermal profiles indicate there will be a very
deep layer of near freezing temperatures in the lowest 10k ft of
the atmosphere. In fact, much of the guidance have now warmed
slightly from this time yesterday, and now suggest a good portion
of this isothermal layer may actually stay just above the
freezing mark tonight. At the same time, there are indications
that the lowest several hundred ft or so, including the sfc, will
probably cool to near or slightly below freezing. This would not
likely be deep or cold enough to refreeze any melted ice crystals
into sleet, but it may create a chc for a light freezing rain
event over our far southern counties overnight into rush hour Thu
AM. However, my thinking is the relatively warm pavement
temperatures, and the assumption that sfc temps will stay very
close to freezing, should mitigate travel impacts during the AM
commute. For now, will likely issue an SPS to address the
possibility of some icy areas on elevated roads and bridges.

More cloudiness and chilly conditions will then rule the remainder
of the short term period. Will stay close to a MOS blend for the
most part with highs in the 30s to near 40, and lows in the 20s.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM CST WED DEC 17 2014

Two weather systems with precipitation potential highlight the main
concern in the long term portion of the forecast. The first occurs
Friday night into early Saturday; the other Monday into Tuesday.

Forecast models have come into much better agreement with the first
system slated to bring a mix of snow and some rain to the region
Friday night and Saturday morning. The faster GFS has slowed down in
better alignment with the ECMWF. Both continue their trends of
shifting the heaviest precipitation south of our immediate forecast
area. The one sticking point remains the low level temperature
profile, but even this is much closer than before. Nonetheless, the
differences are still enough that while the ECMWF indicates all snow
for most of the area, the GFS rather suggests primarily rain except
in our far northern counties. Fortunately, we now have the added
benefit of viewing the end of the NAM run, which carries us into
Saturday. Not surprisingly, it is much closer to the ECMWF than the
GFS on the temperature profile. It also lends a fair degree of
confidence to the overall storm track and synoptic scenario.

Overall, confidence is steadily increasing with respect to
precipitation type, timing, and amount.

(1.) First on precipitation type, it appears as though most of this
event will be in the form of snow north of a zone from the Ohio
River extrapolated across southeast Missouri to about Poplar Bluff.
South of this zone, a mix of rain and snow is still expected, with
more snow near the Ohio River and more rain near the Tennessee
border.

(2.) Timing has been fairly consistent for several days. By now, we
are fairly confident that most of Friday will be dry. The wintry
precipitation will spread northeast across the region Friday night
before coming to an end from the west during the morning hours of
Saturday.

(3.) Precipitation amounts are still in flux at this point, but
potential snow amounts have trended lighter with the southward shift
of the heaviest precipitation. Our best estimate at this point is
that 1 to 2 inches of snow may fall--particularly across the heart
of the forecast area just north of the aforementioned rain/snow
transition zone.

Again, this event is still 2 to 3 days out, so some modifications to
the forecast are quite likely as the models continue to gain a
better handle on the situation. Once the precipitation clears the
area on Saturday, a return to dry and seasonably cold weather is
expected through the remainder of the weekend.

Our next chance of precipitation arrives Monday and especially
Tuesday as upper level energy carves out a deep long wave trough over
the central United States. Temperatures with this series of waves
appear warm enough to support mainly rain Monday, Monday night, and
much of Tuesday. The passage of a cold front will likely force a
changeover to at least some light snow on the tail end of the
departing system Tuesday night. It is way too early to say anything
other than that at this point...

&&

.AVIATION...
Issued at 1050 PM CST TUE DEC 16 2014

While high pressure will begin to build into the region overnight,
clouds are very slow to depart. MVFR overcast cigs are expected to
become broken 09-11z and scatter out after 15z. Keep sct-bkn
clouds aoa 10k for Wednesday becoming broken after sunset in
advance of the next storm system.


&&

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

$$

SHORT TERM...MEFFERT
LONG TERM...RJP
AVIATION...ML





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