Area Forecast Discussion
Issued by NWS Rapid City, SD

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234
FXUS63 KUNR 052341
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
441 PM MST Mon Dec 5 2016

.SHORT TERM...(This Evening Through Tuesday Night)
Issued at 310 PM MST Mon Dec 5 2016

Current surface analysis shows arctic cold front now southeast of
the forecast area, with gusty northwest winds and slowly falling
temperatures behind it. Secondary front across ND and MT. Upper
level analysis shows low over south central Canada, with broad
trof sweeping across the northern high plains right now. Areas of
snow are mostly confined from central SD to southwest SD now, with
some snow showers persisting over the northern Black Hills area.
Conditions have significantly improved over northeast WY, so have
cancelled the winter wx advisory with the afternoon package. Wind
gusts to 50 mph and patchy blowing snow across northwest and west
central SD will continue through the late afternoon and then winds
will gradually decrease this evening.

Arctic air will continue to surge into the area over the next 36
hrs, with the coldest air aloft pushing in late Tuesday
night/Wednesday morning. Areas of snow will taper off quickly
over the area late this afternoon, with only patchy light
snow/flurries expected into tonight over the northern Black Hills
and far northwest SD. Winds will gradually decrease tonight, but
remain breezy over much of the SD plains. Temps will drop into the
single digits and lower teens by early Tuesday morning, with wind
chills mostly in the zero to 15 below zero range by late tonight.

Temps will not rise much on Tuesday, with weak cold air advection
still taking place. Some sun will help to raise temps into the teens
to around 20 degrees. Brisk winds to the northeast of the Black
Hills will keep wind chill values near or below zero during the day
in these areas. The next shortwave will move quickly across the
northern Rockies on Tuesday and into the Central Plains Tuesday
night. Most of the models have pcpn staying south of the forecast
area Tuesday night, but the EC does have some light qpf clipping far
southern portions of northeast WY and far southwest SD, so will keep
low pops there for late Tuesday night. Lows will be near or below
zero in most areas, with wind chills 10 below to 25 below zero. A
wind chill advisory may be needed for a few areas, especially far
northwest SD.

.LONG TERM...(Wednesday Through Monday)
Issued at 310 PM MST Mon Dec 5 2016

Mean troughing over northern NOAM will remain in place through
the period with the region on the northern edge of the jet
stream/storm track. This will support very cold conds as a
modified arctic airmass remains in place. Active shortwave storm
track will support chances for snow once again across the area
this weekend, as a pac origin system traverses fast westerly flow.
The main belt of snow associated with this system looks to remain
over the northern half and north given collocation of
fgen/forcing. Otherwise, the GFS and ECMWF start to deviate
outside of the period toward early next week, with flow/height
differences supporting varying forms of another possible arctic
outbreak, which will likely be driven by the amount of ridging in
the eastern pac (into the western CONUS).

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 437 PM MST Mon Dec 5 2016

Arctic air will continue to pour into the area through the
forecast period with gusty northwest winds on the SD Plains. Areas
of MVFR/IFR CIGS expected. Local IFR VSBYS due to leftover -SN
will end on the SD Plains this evening.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 9 PM MST this evening for SDZ001-002-012>014-
     025-026-031-032-072-073.

WY...None.
&&

$$

SHORT TERM...26
LONG TERM...JC
AVIATION...Helgeson



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