Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 250946
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
346 AM CST Sat Feb 25 2017

.SHORT TERM...(Today and tonight)
Issued at 343 AM CST Sat Feb 25 2017

Early this morning the region was under northwesterly flow aloft as
the mid-level trough continued to shift eastward into the Great
Lakes region.  Surface high pressure was situated over western KS,
so the combination of clearing skies and northwesterly winds was
resulting in decent cold-air advection with low temperatures
plunging into the mid teens to mid 20s from north central to east
central KS.  This surface high will shift southeastward into
Oklahoma today, which will cause northwesterly winds to back to the
south/southwest this afternoon.  While afternoon temperatures are
expected to remain cooler than the seasonal normals, the afternoon
wind shift to the south will help to at least boost highs into the
upper 30s to mid 40s.

These southerly winds will persist tonight, but models show the wind
speeds increasing a bit overnight which will cause temperatures to
actually rise a few degrees after midnight into Sunday morning.
Fairly zonal mid-level flow will set up over the central U.S. behind
the exiting trough, with models showing an embedded weak shortwave
trough approaching the area by Sunday morning.  Model soundings show
increasing mid-level moisture after midnight across central KS ahead
of this approaching wave, but there is low-level dry air that will
need to be overcome.  While there are some slight model
discrepancies with regards to how quickly this mid-level moisture
overcomes the dry air, several models suggest that some light
scattered precipitation may begin to develop across central KS by
the 09z-12z period, so have added slight chance PoPs.  Despite the
slowly rising temperatures into Sunday morning, conditions should be
cool enough for any initial precipitation to be in the form of
snow.

.LONG TERM...(Sunday through Friday)
Issued at 343 AM CST Sat Feb 25 2017

The mid/long term period continues to show signs that temperatures
will be near or above normal through the period. Also, while
previous model runs had a rather muddled depiction of the timing of
various short wave troughs early this week, we are now seeing
significantly greater agreement focusing on Sunday morning, Monday
evening, and Tuesday night for precipitation chances. These precip
chances will directly impact temperatures as any locations with
precip especially early Sunday and Tuesday night will be markedly
cooler due to wet bulb effects but at this point have played more of
a middle ground on temperatures given general uncertainty in timing,
intensity, and location of precip.

Precip chances early Sunday will be driven by a combination of DPVA
and jet speed divergence aloft while focused isentropic ascent will
be ongoing in the lower levels. There is also a fair amount of dry
air to be overcome in the low levels but vertical motion seems to
probably be sufficient to overcome the dry air and result in an area
of generally light precipitation mainly focused in east central KS.
Precip type is also tricky as wet-bulb effects will play a role and
could see transition between rain and snow with the heaviest precip
areas more likely to favor a change over to snow.

In the wake of that system, a new surface cyclone will develop in
eastern Colorado Monday evening. Warm advection and isentropic
ascent over eastern KS may support development of rain showers
Monday evening as the surface low develops east and strong moisture
advection focuses into the eastern half of the forecast area. This
activity will rather quickly  move east, and could develop north and
east of the local forecast area entirely but at least warrants small
chances for rain.

Perhaps the best looking chance for interesting precipitation in the
area will be on Tuesday night into Wednesday morning. This comes in
response to a decent vorticity maximum moving overhead with ample
mid/upper level moisture and rather impressive frontogenesis across
the forecast area. There are two main questions in this period: 1)
Will the lift be sufficient to overcome substantial dry air in the
low levels? 2) Will the low level temperature profile support rain,
snow, or a mix? Current thought is that the lift will be strong
enough to overcome the dry air, especially in a band oriented
somewhere in this general region where the stronger frontogenesis
pairs with the mid level moisture and slantwise or even convective
instability. Also have support from nearly every member of the
GEFS for some modest precipitation in the forecast area. Would
also expect this precip to start off as rain but then to change
over to snow especially where the heaviest precipitation develops
and the temperature profile wet-bulbs down to support snow. After
this point, expect a dry and generally warm period through
Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1138 PM CST Fri Feb 24 2017

Expect VFR conditions for the next 24 hours.


&&

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

$$

SHORT TERM...Hennecke
LONG TERM...Barjenbruch
AVIATION...Gargan



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