Area Forecast Discussion
Issued by NWS Topeka, KS

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836
FXUS63 KTOP 012125
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
325 PM CST MON FEB 1 2016

.SHORT TERM...(This Evening through Tuesday Night)
Issued at 250 PM CST MON FEB 1 2016

The incoming storm system is, more or less, evolving as advertised
this Monday afternoon. Surface cyclogenesis is ongoing while a broad
but so far loosely organized precipitation shield is overspreading
much of western Kansas, Colorado, and into Nebraska. In the local
area, light rain will be possible into early evening as these weak
impulses move across the region with areas of light precipitation.
This may mix with periods of snow mainly in/near Republic county but
accumulation should be pretty much 0 through 9 PM or so.

The main precipitation shield will move out of central Kansas and
across the local area between roughly 10 PM and 6 AM. Expect to see
embedded thunderstorms within this area of moderate rain, with an
isolated lightning strike or two not out of the question even within
the snow area. Instability is not particularly strong and the storms
will be mainly elevated, but with the very strong winds just above
the surface, there is a small chance for a few downdrafts to bring
some locally stronger winds down to the surface. Within the rain
area, expect generally from 0.50 to 1 inch of rain.

The snow forecast remains quite difficult even only a few hours in
advance of the storm. And really, the only reason it remains
difficult is because the rain/snow cutoff line continues to
fluctuate slightly regarding the location of what should be a very
sharp gradient in snow amounts. Additionally, warm ground
temperatures and even warm air temperatures during snowfall will
induce a bit of melting and compacting more than normal. At the same
time, when the snow does begin, the rates should be extremely heavy
with convective snowfall initially and transitioning to more of a
frontogenesis and dynamics-driven snowfall which should still see
moderate rates. Would not be surprised to see snowfall rates exceed
2" per hour for a couple of hours within the heavy snow area. Models
remain in fairly good agreement in terms of where the snow/rain
cutoff will be throughout the night, but still with enough of a N/S
variation to keep question marks in the snow total forecast. High-
Res guidance such as the HRRR and RAP seem to be initializing a bit
warm but still get cold enough in far northwest parts of the CWA
during the heavy precip period to support heavy snow accumulation.
Still looking for the winter-storm-type accumulation amounts near
and north of the Concordia to Washington line, with sharply lower
amounts south of that line.

There appears to be a high likelihood that the dry slot will
overspread the majority of the forecast area during the day on
Tuesday, although again with a rather sharp dry-to-snow cutoff in
the far northwest corner of the forecast area so some additional
snow will remain possible during the morning within the warned area.
Then during the afternoon or early evening, a vort max will wrap
around the main system and may support another quick shot of light
snow on the order of an inch or more, mainly in areas north of I-70.
Winds will continue to be an issue for any areas that experience
heavy snow as there will be some reduced visibility and drifting.
Should note though that the winds appear to have a lull on Tuesday
as the center of the surface low moves overhead.

.LONG TERM...(Wednesday through Monday)
Issued at 250 PM CST MON FEB 1 2016

No major changes needed in the extended as upper wave pattern favors
a dry northwest flow with upper troughs passing to the northeast and
southwest of the CWA. Northwest winds are initially gusty behind the
departing wave Wednesday morning, before gradually diminishing to
around 10 mph at sunset. Cold air advecting from the snowpack in
Nebraska was shown in decent agreement with respect to temperatures
on Wednesday and Thursday with readings in the 30s and overnight
lows in the teens and 20s. Southerly winds return Thursday onward
with mostly sunny skies return and highs rebound to the upper 40s
through the weekend. Next cold front and potential system arrives by
Monday with much uncertainty in guidance on any available
moisture.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1144 AM CST MON FEB 1 2016

Very challenging 24 hour period for the 18z TAF forecast.
Generally, this afternoon should remain VFR with increasing
easterly winds beginning to gust into the 20kt range. Into the
overnight period expecting precip in the form of rain and even
some thunderstorms at the KTOP/KFOE terminals. As the storm system
approaches the terminals and begins to deepen more, winds will
continue to increase and gust up to the 30kt range. Beginning
around the 4z and up until the 13z time frame, expect to see
CIG/VIS reach into IFR categories. Not ruling out lower categories
at this time with heavier areas of rain. Lower confidence in that
at this time though, so have only decreased categories to IFR. By
morning though, it is reasonable to believe we improve back to VFR
quickly as the dry slot of air gets pulled into the region before
the winds shift again but likely after or near the very end of the
forecast period as the low center passes nearly right over the
terminals. Have not included a wind shift veering all the way to
the WNW as a result and winds could vary in speed a bit during the
early morning hours as the change takes place.


&&

.TOP Watches/Warnings/Advisories...
Winter Weather Advisory from 6 PM this evening to 6 PM CST
Tuesday for KSZ010-011-021-022-034.

Winter Storm Warning from 6 PM this evening to midnight CST
Tuesday night for KSZ008-009-020.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Bowen
AVIATION...Drake



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