Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 210310
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
910 PM CST Sat Dec 20 2014

.MESOSCALE DISCUSSION...
Issued at 910 PM CST SAT DEC 20 2014

Distinct cloud line following the sharp surface ridge axis this
evening from northeast to southwest across Southern Illinois and
Southeast Missouri. The 5km resolution of the NAM-WRF model
guidance appears to be approximating the persistence of the cloud
line well through the overnight hours. Adjusted temperature and
dewpoint forecast to reflect diabatic variations in
radiation/advective issues under the cloud cover. See some
potential for patchy fog along the cloud edge along the clear sky
side...so added overnight. Not ready to issue any statement until
coverage of light fog becomes more prevalent.

No other changes made beyond first period (tonight) forecast at
this time.

&&

.SHORT TERM...(Tonight through Monday night)
Issued at 306 PM CST SAT DEC 20 2014

Forecast confidence is relatively good through the short term
period.

Decreasing low level moisture, high pressure at the surface, and
zonal flow aloft are finally taking their toll on the stubborn low
level cloud cover.

These same conditions should produce the opportunity for star gazing
tonight and plenty of sunshine on Sunday, especially east of the
Mississippi river. As is often the case this time of year, the lack
of cloud cover won`t last long.

With the passage of a short wave Sunday night, expect an increase in
cloud cover but no precipitation due to a relative lack of deep
moisture and our being in somewhat of a col between the sub-tropical
jet stream to the southeast and the polar jet stream nosing in from
the plains.

As a storm system develops over the northern plains, a sharp H5
trough extending southwest from it across the central plains will
push a cold front toward our region. This combined with the eventual
merging of the aforementioned jet streams over our area and an
increase of deep moisture will produce increasing precipitation
chances from the west through the end of the period. Models still in
minor disagreement on the exact location of the surface boundary at
the end of the period, but the end result should be nearly the
same.

.LONG TERM...(Tuesday through Saturday)
Issued at 306 PM CST SAT DEC 20 2014

Models take a surface low on a similar track but with different
timing Tuesday through Wednesday night.  Models bring the low
northeast across the PAH forecast area Tuesday night, then the ECMWF
tracks the low into the Great Lakes region 6 to 12 hours faster than
the GFS and GEM.  This leads to better confidence in keeping likely
pops across our region Tuesday and Tuesday night, but timing of the
low leads to some uncertainty how quickly colder air will filter
into the region on Wednesday.  Tuesday precipitation will be all
rain, then as temperatures drop off into the middle to upper 30s
Tuesday night, went with a rain/snow mix after 06z Wednesday mainly
across the western two thirds of our counties.  On Wednesday, high
temperatures should be around mid morning, with steady or falling
temperatures in the afternoon.  Continued with a rain/snow mix
across most of our forecast area Wednesday morning, spreading east
across all of our counties Wednesday afternoon.  A little light snow
may linger in our far eastern counties Wednesday night.  Snow
accumulation is not expected at this time.

For Christmas day, conditions should be dry with plenty of
sunshine.  Winds will shift back to the southwest to south, helping
temperatures rebound to near seasonal readings in the 40s.
Moderating conditions will continue into Friday with the breezy
south to southwest winds.  On Friday, GFS and ECMWF take low
pressure system north of our region, dragging a weak cold front
through the middle Mississippi and lower Ohio valleys.  Models
generate some light QPF, especially east of the Mississippi river.
Continued with chance/slight chance pops for Friday into Friday
evening, possibly changing to a rain/snow mix if enough moisture
lingers as low temperatures fall into the upper 20s to lower 30s.
Dry and cooler conditions are expected for Saturday as high pressure
builds into the central U.S..

&&

.AVIATION...
Issued at 532 PM CST SAT DEC 20 2014

Although a little westward progression of the cloud cover may
still clear out things for KCGI, the late day clearing for this
area appears to have stopped for now and a resumption of upper
MVFR ceilings will likely stay in place for the forecast period.
There is even a period after midnight that light drizzle may be an
issue.

Otherwise, VFR conditions should persist for the KPAH, KEVV, KOWB
TAF sites through the end of the forecast period under light
southeast winds. Some diurnally induced MVFR ceilings was briefly
included during the morning hours at KPAH.


&&

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

$$

MESOSCALE...Smith
AVIATION...Smith





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