Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 071715

National Weather Service Topeka KS
1115 AM CST Wed Dec 7 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 321 AM CST Wed Dec 7 2016

Flow aloft remains rather quick in longwave troughing with deep
upper low over southwestern Ontario and another weaker wave making
its way east into Wyoming and Colorado early this morning. Weak
north low level flow continues in northern Kansas on the south
edge of a broad surface ridge. Increasing mid cloud has kept
temperatures fairly steady in recent hours but dewpoints continue
to fall with some values near 10F in northeast Kansas. Radar
imagery showing a few areas of dBZ values above 20, but much of
this is near 10kft above the surface. Light snow was falling over
extreme northwest Kansas where ceilings are around 4kft.

Much of the model guidance is similar with a couple of areas of
enhanced light snow chances today. Band of snow developing in
northwest Kansas to continues to form east-southeast to along I-70
this morning, with a second area forming this afternoon along and
southeast of I-35 where best frontogenesis occurs in weakly stable
air and temperatures in this enhanced lift are in/near dendritic
snow growth values. Both bands are rather short-lived and
ageostrophic responses are rather weak however. Models are in
general over- forecasting overnight precip amounts and continue to
keep low levels rather dry, keeping anticipated snow totals low.
Still looking like most locations will see less than an inch, with
some isolated areas to near 2 inches possible. Temperatures should
stay rather steady with cloud cover being thick through much of
the day but column still supports all-snow and somewhat higher-
than-normal snow ratios in cold air aloft. The passage of the
upper wave brings a quick loss of isentropic lift and any snow to
an end early this evening with lows in the 8-16 range tonight as
skies clear and Canadian surface ridge pushes in.

.LONG TERM...(Thursday through Tuesday)
Issued at 321 AM CST Wed Dec 7 2016

A rather benign extended forecast awaits for NE Kansas with
multiple rounds of cold weather being the biggest headlines.
Surface ridge axis centered over the High Plains at the onset of
the period will slide eastward during the day on Thursday and
early Friday, bringing the coldest temperatures of the season on
Friday morning. Current forecast lows for Friday morning follow
close to MOS, which given the light winds and possibility of some
snow cover (especially in the western CWA), would be more
realistic than the much warmer raw model guidance.

Good return flow sets in behind the departing ridge by late
Friday into Saturday. GFS soundings show excellent daytime mixing
in the BL with winds at the top of the layer pushing 35+ kts.
Upped highs by several degrees for Saturday as a result. This
warm-up will be short-lived as a Southern Plains cyclone ejects
E/NE and drags a cold front south, which will herald the arrival
of more arctic air for the early to middle part of next week.
While solutions vary on the evolution of the surface cyclone and
resultant precipitation placement, there is a much stronger CAA
signal amongst the GFS/EC/Canadian. Started trending down highs
below the blended solution for Monday and Tuesday to better
reflect the increasing likelihood of this scenario.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1114 AM CST Wed Dec 7 2016

Reduced visibilities and ceilings are now being seen at all sites.
Light snow will continue to fall for the next couple hours with
the highest intensities and lowest visibilities until 19Z. Skies
will begin to clear from northwest to southeast late in the
afternoon with VFR conditions expected after 22-23Z.




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