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000
FXUS63 KTOP 080538
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1138 PM CST Sat Dec 7 2013

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 246 PM CST SAT DEC 7 2013

Light snow accumulations continue to be the focus for the overnight
into Sunday time frame.  Isentropic lift underway out west and
increases over the forecast area into the late night hours before
dropping off after sunrise.  Still don`t see overlapping
instability/lift for heavier snow bands, but rather an event several
hours long of light snow that bring some accumulation to the area.
Better lift continues to move across the counties north of I70,
while areas south and east still get a chance for some light snow
accumulations but less. Still looking at near 3 inches around the NE
border with an inch or less I35 and southeast with 1-2 in between.
West of Manhattan may see half an inch before midnight with rest of
the area seeing accumulations mainly in the midnight to 6am window
with some diminishing light amounts before noon.

Battle with the dry air then becomes the focus, and whether or not
there will be enough ice for remaining light precip in the afternoon
to stay snow or changeover to light freezing drizzle.  NAM is
coldest of them all and keeps top of the mixed layer and lift
generally in the -10 to -12 range, while GFS is coming in warmer and
less unstable down in the lowest levels.  Think the colder solution
is more appropriate given dynamic cooling with the precipitation,
but with the differences between the temperature guidance and the
increasing depth of the dry air in the snow growth layer, will add a
chance for light freezing drizzle east and south of Topeka for the
afternoon hours.  With most accumulations falling before the
afternoon, not expecting much either way in terms of snow or drizzle
accumulation in the afternoon for this area.  Lows fall to the teens
tonight but increasing clouds and a shift around late day to
southerly winds at the surface should bring highs back into the 20s
on Sunday.

.LONG TERM...(Sunday Night through Saturday)
Issued at 246 PM CST SAT DEC 7 2013

Late Sunday the mid level shortwave responsible for the snow lifts
NE of the area into the upper Midwest. That system will drive a
reinforcing shot of cold air behind a weak front that moves through
the region Sunday evening. By 00Z Monday the front should be located
across the forecast area increasing the low level lift as it
progresses southeastward. Forecast soundings show dry mid levels
before the front arrives although the low levels maintain saturation
especially in the eastern portion of the forecast area. Temperatures
within this layer of lift and saturation range from -5 to -12, which
is cold enough for snow, but could not rule out the formation of
freezing drizzle as well. This front and associated lift quickly
exits the area by 03Z Monday with very little measurable
precipitation if any at all.

The reinforcing shot of cold air brings low temperatures back into
the low 10s in east central KS to near zero in north central KS for
Monday morning. Wind chill values will again approach -15 in
northern KS. During the day Monday skies will be partly cloudy with
highs in the mid to upper 10s. On Monday night the main trough
swings out of the SW CONUS bringing a slight chance of snow just
south of the area as an area of frontogenesis and upper level
divergence coincide over southern KS. Tuesday morning low
temperatures range from the mid 0s across northern KS to the low 10s
in east central KS. A slight warming trend will then begin as the
mid/upper level pattern becomes less amplified across the western US
and eastern pacific. The flow will remain out of the NW so expect
temperatures still below normal, but moderating from this recent
arctic outbreak. There will also be a series of cold fronts that
push through the area although the lack of moisture keeps things
dry. With the exception of Wednesday highs will generally be in the
30s even close to 40 by Friday...with overnight lows in the 10s and
20s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Sunday Night)
Issued at 1137 PM CST SAT DEC 7 2013

For the 06z TAFs, areas of light snow had begun to develop during
the evening hours over far north central Kansas. This activity is
expected to become more widespread through the overnight hours into
Sunday morning. With this developing snow, expect cigs/vis to drop
to MVFR conditions, however borderline IFR/MVFR cigs cannot be ruled
out in any areas of heavier snow. This precipitation will begin to
diminish in intensity by late morning into the afternoon hours. It`s
worth noting that model soundings continue to show the potential for
some light freezing drizzle to mix in with light snow near KTOP/KFOE
during the afternoon and early evening hours. Any lingering light
precipitation should finally exit the area by 00z-03z Monday with
cigs slowly improving to high-end MVFR conditions.



&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...67
LONG TERM...Sanders
AVIATION...Hennecke