Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 171134
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
534 AM CST Sun Dec 17 2017

.UPDATE...
Issued at 531 AM CST Sun Dec 17 2017

For aviation section only.

&&

.SHORT TERM...(Today through Tuesday night)
Issued at 325 AM CST Sun Dec 17 2017

A weakening mid level short wave will lift northeast through the
Ohio Valley today. Light rain now spreading northeast into se MO
will continue to move northeast into the region this morning.
Highest chances for measurable precip will be over southeast MO
and wrn KY. Even there though, amounts will be quite light,
generally a tenth inch or less. Most of the rain will move east of
the forecast area this afternoon. However, a good deal of low
level moisture will be left behind, trapped beneath a sharp low
level temperature inversion. Areas of drizzle and fog will be
possible tonight into Monday morning.

Not expecting to see much if any sunshine through the short term
as another southern stream system will be moving east into the
southern plains Tuesday and Tuesday night. Though most of the
precip with this system should stay down over AR/TN, abundant
clouds will likely make it up into our area. All of this points to
little diurnal change in temps, most likely less than 10 degrees
from max temps to min in most locations Monday and Tuesday.

.LONG TERM...(Wednesday through Saturday)
Issued at 230 AM CST Sun Dec 17 2017

The ejected southwest U.S. low is progged by most of the medium
range deterministic and ensemble guidance to move across Arkansas
and Tennessee during the day Wednesday with showers the dominant
weather type. The northern extent of the precipitation may vary due
to subtle mesoscale influences, but may not be resolved until the
Monday/Tuesday forecast package.

Brief zonal flow will overspread the WFO PAH forecast area Wednesday
night into Thursday, before the northwest U.S./eastern Pacific low
moves onshore and quickly into the desert Southwest. This feature
will push the WFO PAH forecast area back into southwest flow aloft.
This low is forecast to phase in with the northern Canada trough and
low, tapping into the Arctic air flow. The GFS and ECMWF guidance
have been consistent in deepening the cold dome of air into the
region by Friday night, sharpening the baroclinic zone in the
southwest flow aloft. With a strong thermal gradient expected with
the a frontal passage Friday afternoon and evening, could see a
quick transition to light snow/snow flurries late Friday night.
Given the antecedent warm temperatures and lower intensity of
precipitation, do not anticipate any measurable accumulation at this
time.

Colder air will be in place Saturday and Saturday night across the
WFO PAH forecast area with the GFS/ECMWF suggesting 850 mb
temperatures ranging from -4C to -10C.

The forecast uncertainty begins Saturday night, as the
ECMWF/GFS/Canadian guidance dive a potent shortwave into the central
Rockies on the western side of an expansive trough over the U.S. The
net effect is to deepen the main low/trough over the upper Midwest
and northern Great Lakes, enhancing and reinforcing the cold air
toward the WFO PAH forecast area.

There is some question as to how much moisture will be entrained
into the upper low, and the translation of the sharp baroclinic zone
over the Southeast U.S. and Tennessee Valley. This will determine
the potential for any snow development and accumulation early
Sunday. There is still quite a bit of spatial variability for the
northern edge of the baroclinic zone during this time period, so the
for of precipitation coverage and type still remains uncertain.

&&

.AVIATION...
Issued at 531 AM CST Sun Dec 17 2017

Light rains will continue to march northeast across the region
this morning, though conditions should stay VFR for the most part.
Lower MVFR conditions expected to set in around sunset, then IFR
with drizzle/fog possible aft 06z.

&&

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

$$

UPDATE...GM
SHORT TERM...GM
LONG TERM...Smith
AVIATION...GM


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