Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201136

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
436 AM MST Fri Jan 20 2017

.SHORT TERM...(Today Through Saturday Night)
Issued at 231 AM MST Fri Jan 20 2017

Water vapor shows large upper trof along the west coast, with lead
short wave ejecting through the Four Corners. At the sfc, trof is
located over cntrl SD with weak cdfnt shifting east of the
nrn/cntrl Rockies.

Short wave over the Four Corners will continue tracking newd today
and into the cntrl plains by tonight. Weak cdfnt will shift ewd
into the nrn plains today and tonight, resulting in some light
rain/snow across nern WY today and the Blkhls and southern SD
tonight. Moisture is limited so nothing significant expected.
Temps will be cooler than yesterday, but still a few degrees above

Similar temps expected on Saturday but with a bit more wind
behind the departing wave. Could see a bit of light snow across
far nwrn SD Saturday night as moisture wraps around newly formed
upper low over the upper midwest.

.LONG TERM...(Sunday Through Thursday)
Issued at 231 AM MST Fri Jan 20 2017

Dry weather is expected Sunday into Monday as an upper level low
drifts well northeast of the region and weak ridging crosses the
northern high plains. Highs on Sunday and Monday in most areas
will be near average.

A broad upper level trough will cross the Rockies Monday into Monday
night and then across the plains through Tuesday. Latest medium
range models all show an upper low developing somewhere across
Nebraska as the trough moves east across the region. Still have some
differences between the models with regard to timing and track of
the system, but they look to be in better agreement compared to 12Z
Thursday runs. GFS is still more northerly with the track of the low
and a bit faster compared to the EC and GEM, but all show a fairly
quick moving system. The focus for more significant snowfall at this
time looks to be across portions of eastern WY, southern SD, and
northern Neb, where there is potential for several inches of snow
with the current projected track for later Monday night into
Tuesday. With the system still several days away, there is still
plenty of uncertainty at this point and any shift of the system to
the north or south would obviously affect snowfall potential across
the forecast area.

Below average temperatures look likely for the middle of the week.
Weak disturbances passing through the back side of the trough could
bring some snow showers at times, especially across far northeast WY
and the northern Black Hills area.


.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 435 AM MST Fri Jan 20 2017

Western edge of low clouds will clip far eastern portions of the
forecast area this morning, with IFR/LIFR cigs and patchy fog near
and especially east of a line from HEI to D07 to PHP to ICR. An
upper level disturbance will slowly move north and east into
western portions of the CWA later this morning, with MVFR/IFR
conditions developing over northeast WY, along with areas of light
snow and flurries. These conditions will spread east into portions
of western SD later this afternoon and evening.




SHORT TERM...Johnson
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