Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 201150

550 AM CST Sat Dec 20 2014

Issued at 550 AM CST SAT DEC 20 2014

The AVIATION section has been updated for the 12Z TAF issuance.


.SHORT TERM...(Today through Monday)
Issued at 315 AM CST SAT DEC 20 2014

The last of the light snow and sleet will be pushing east out of
the Evansville Tri State in the next hour or so. Have not heard of
any accumulations or impacts. The bigger question going forward is
how long will the lower clouds linger over the region. Looking at
the GFS and NAM RH, it appears that the cloud layer is
substantial and would not likely dissipate on its own. Low-level
winds are weak, so advecting them out of the area does not seem
very likely either.

Made some last minute adjustments to hang onto mostly cloudy
skies through the day over southeast Missouri and southern
Illinois. Undercut guidance a bit in these areas, and leaned
toward the warmer MAV highs in the southeast where some clearing
is forecast.

The model consensus is for the clouds to dissipate heading into
this evening, and with the surface high overhead, it should be a
cold night in most locations. Went close to consensus for lows,
and may have to watch for some fog development, especially where
clearing doesn`t occur until the late afternoon or into the
evening. Did not insert fog into the forecast at this time,
because of uncertainties in the sky cover forecast.

The pesky surface high will begin to loosen its grip on the region
Sunday, allowing a light southeast wind to develop in most
locations. If we get some decent sunshine, we should see highs
closer to the warmer MAV numbers, if not the cooler MET numbers
will be better.

The NAM...GFS and ECMWF have delayed the arrival of increasing low-
level moisture and drizzle potential until early Monday.
Therefore, will not have any mention of precipitation until after
12Z Monday. A decent southeast wind is expected throughout the
area Sunday night, and there will eventually be some increase in
cloud cover late. Therefore, should see lows on the mild side
of guidance.

The ECMWF and GFS continue to differ in timing precipitation
through the area Monday. The GFS is not nearly as wet as the ECMWF
Monday, and I really don`t have a good feel for which model is
better. This is not a high confidence situation due to the rapid
development of the upper trough. The details of QPF are not likely
to be well handled just yet. Left mainly 25-30% PoPs in the
forecast for Monday. Strong south winds will develop Monday, and
that should finally help us to warm up into the 50s, if the clouds
are not too thick or widespread. The consensus of available
guidance should do pretty well for highs.

.LONG TERM...(Monday Night through Friday)
Issued at 315 AM CST SAT DEC 20 2014

The upper-level flow pattern will become much more amplified during
the long term period. The flow pattern will remain very progressive.
The result will be a series of fast-moving fronts and low pressure
systems that will bring changeable weather through the week.

As far as the daily details...
A strong cold front will move east across our region on Tuesday as a
500 mb shortwave digs southward through the Plains. The digging
shortwave will provide plenty of forcing for precipitation along and
ahead of the front Monday night and Tuesday. Lapse rates will
steepen with the approach of the trough, which should cause the
precipitation to take on a showery character. Thunder cannot be
ruled out based on the small elevated capes shown by gfs model
soundings. A southwesterly low level jet of 40 to 50 knots is
indicated by the gfs early Tuesday, which will contribute to weak
instability and increasing low level moisture.

Late Tuesday night and Wednesday, the mid levels will gradually dry
out as the negatively-tilted shortwave trough axis lifts northeast
across the Ohio Valley. The primary surface low will be over the
western Great Lakes region, producing a colder west to northwest low
level flow. There may be a changeover to snow late Tuesday night
before the mid levels dry out. The 00z ecmwf hints at a weak
secondary low forming along the front over central Kentucky late
Tuesday night. If this occurs, it could prolong the precipitation
long enough for some light accumulations of snow in areas east of
the Mississippi River. The 00z gfs and its ensemble mean do not
indicate this secondary low. Regardless of the model of choice,
there will likely be scattered snow showers on Wednesday under the
cold/unstable/cyclonic flow. These could be mixed with rain in
southern areas.

On Christmas eve and Christmas Day, the low-level flow will turn
southwesterly in advance of the next upper trough advancing through
the western states. Christmas Day appears dry and mild, but rather

On Friday and Friday night, the model consensus is that another cold
front will move east across our region. This front will be preceded
by showers on Friday, which may change to snow showers before ending
Friday night. The upper-level trough associated with this front
appears weaker than the Tuesday system, so forecast precipitation
chances and amounts are lower.

On Saturday, it appears a surface high will build east across the
Mississippi Valley, bringing colder and drier air.


Issued at 550 AM CST SAT DEC 20 2014

A large, solid mass of lower VFR clouds covers the entire region
this morning. It doesn`t look good for them to scatter or clear.
Hopefully, subsidence in the cloud layer will be strong enough to
help the clouds dissipate over portions of the area this
afternoon. In the meantime, would not be surprised to see a few
hours of an MVFR ceiling at KCGI this morning. If clouds do
scatter out or clear late this afternoon, that could set the stage
for fog development. At this time, that seems most likely at KEVV.




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