Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 202050

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
150 PM MST Sat Jan 20 2018

.DISCUSSION...(This Evening Through Saturday)
Issued at 117 PM MST Sat Jan 20 2018

Water vapor shows deep trof over the western CONUS with strong
jet extending from just west of the Four Corners northeastward
through WY and SE MT, then eastward across ND and northern
MN. Cloud tops are expanding/cooling across central/eastern WY. At
the surface, low center continues to deepen over SE CO. A band of
rain/snow mix extends from far SW SD through central SD, but
relatively warm surface temps not allowing any snow accumulation
quite yet.

Expect snow to gradually expand northeastward this evening and
overnight as right entrance region to strongest part of
aforementioned jet spreads into western SD. Overall, not a lot of
change to the forecast with models in fairly good agreement
placing the heaviest band of snow towards the NEB border. Warning
type snows expected along our southern tier of counties in SD,
with advisory snow further north to near the I-90 corridor in
western SD. Advisory snows also expected across southern Campbell
and Weston counties in NE WY. The only appreciable change to the
current headlines was to add Haakon county to the Winter Wx
Advisory as it`s possible Philip in far southern Haakon could get
several inches.

Snow will begin to wind down in NE WY early Sunday, then across
western SD during the afternoon hours, and finally across South
Central SD in the evening and overnight. Winds are not expected to
be particularly strong with this system, but some blowing snow
possible Sunday afternoon/night on the plains of SW and South
Central SD as stacked low winds up over KS. However, snow is
expected to be fairly wet and do not expect any major impacts from
any blowing snow. It still looks as if South Central SD will
remain just to the northwest of developing TROWAL Sunday night.

Dry and cool conditions then will prevail through much of the
week. Next upper trof will cross the Plains Friday-Saturday and
may bring widespread precipitation.


.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1013 AM MST Sat Jan 20 2018

Areas of MVFR conditions with light snow or mixed pcpn will
persist over much of northeast WY and parts of western SD this
afternoon. Snow in IFR conditions with the main storm system
will expand across northeast WY in the afternoon and then across
the Black Hills and southern SD late this afternoon and tonight.
MVFR/IFR conditions can be expected across these areas with the
snowfall, along with some areas of LIFR conditions, especially
across the Black Hills and far southern SD. Mostly VFR conditions
are expected across far northeast WY into northwest SD this
afternoon and tonight with little or no snowfall.


SD...Winter Storm Warning from 5 PM this afternoon to 2 AM MST Monday
     for SDZ042>044.

     Winter Storm Warning from midnight tonight to 6 AM CST Monday
     for SDZ046-047-049.

     Winter Storm Warning until 5 PM MST Sunday for SDZ027-029-041.

     Winter Weather Advisory from 5 PM this afternoon to noon MST
     Sunday for SDZ026-028-030-031-074.

     Winter Weather Advisory from 8 PM this evening to 2 AM MST
     Monday for SDZ032.

WY...Winter Weather Advisory until noon MST Sunday for WYZ055-058.



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