Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 101756

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1056 AM MST Wed Jan 10 2018

.DISCUSSION...(Today Through Tuesday)
Issued at 240 AM MST Wed Jan 10 2018

Upper analysis shows a trough in the northern stream coming into
phase with another trough/low pressure center in the southern
stream. The combined upper trough will cross the forecast area
today and tonight. At the surface, a weak low pressure center is
currently located over northeastern Wyoming, connected by a
surface trough to the main low over central Manitoba. A cold front
extends from the Manitoba low into Montana early this morning.

The cold front will sweep southward into the forecast area a
little later this morning and then will move from north to south
today reaching south central South Dakota later this afternoon.
Post frontal lift combined with synoptic scale enhancement from
the upper trough will lead to light snow across the area today
into tonight. Due to the relatively warm surface temperatures, the
precipitation could briefly start as a little light rain, but
should quickly changeover to snow as the colder air rushes in
behind the front on gusty northwest winds. The system looks to be
moving through quite rapidly so have lowered the forecast snow
totals at most locations. Still it appears that areas with the
most snow accumulation will be across far northeastern Wyoming and
the northern Black Hills, into northwestern South Dakota during
the late morning into this afternoon with another area over far
south central South Dakota this evening. Snowfall totals will
mostly be in the 1 to 3 inch range, with some locally higher
amounts possible across far northeastern WY, the northern Black
Hills and far northwestern SD. Parts of far south central SD
could also see some locally higher amounts if the system slows
slightly this evening, as indicated by a few of the models.

Winds will be the other issue as post frontal 15 to 30 mph winds
develop across much of the area, with some gusts to around 40 mph
likely across the northwestern and west central SD plains during
the afternoon and early evening. Areas of blowing snow are
expected to develop during the afternoon with reduced
visibilities. Due to the potential for hazardous travel conditions
developing as temperatures fall, will keep the Winter Weather
Advisory in place. Snow will taper off from west to east during
the evening and into the overnight hours, with winds gradually
diminishing as well. Lows by Thursday morning will mostly be in
the 5 below to 5 above zero range with wind chills 10 below to 25

On Friday and Saturday a wide temperature spread will exist across
the forecast area with temperatures in the upper 20s to lower 30s
over parts of northeastern Wyoming the Black Hills and far
southwestern South Dakota with highs only in the single digits
above zero over parts of northwestern South Dakota. A weak
shortwave will bring another chance of light snow on Thursday
night into Friday.

A brief warmup is possible on Sunday before another shot of
colder air arrives for the early part of next week. We could also
see some light snow or flurries late in the weekend into the early
part of next week as the colder air moves in.


.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1051 AM MST Wed Jan 10 2018

A fast moving storm system will cause conditions to continue to
deteriorate this afternoon, before improving again overnight. Snow
and blowing snow will cause widespread IFR and some areas of LIFR
conditions this afternoon and evening. Conditions will improve to
MVFR and VFR overnight as this system moves eastward. Gusty
northwest winds will continue through the forecast period.


SD...Winter Weather Advisory until 11 PM MST this evening for SDZ001-

     Winter Weather Advisory from 5 PM MST /6 PM CST/ this afternoon
     to 5 AM MST /6 AM CST/ Thursday for SDZ044-046-047-049.

     Winter Weather Advisory until 2 AM MST Thursday for SDZ026-

WY...Winter Weather Advisory until 11 PM MST this evening for WYZ054-



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