Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 090526

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1026 PM MST Thu Dec 8 2016

Issued at 747 PM MST Thu Dec 8 2016

Main fcst challenge this evening revolves around how low temps
will get over snow covered areas before waa push stops the fall.
Satellite pictures show thin veil of high clouds dissipating as it
moves over wrn SD with with main veil of clouds still over sern
WY. 2WX/GCC and SPF have already fallen past current fcst lows and
cont to slowly fall under good radiational cooling conditions with
IEN/PHP/D07 also quickly approaching fcst lows. Have knocked some
places down a category and may need to chase them further but will
see what cloud cover looks like by 05z.


.SHORT TERM...(This Evening Through Friday Night)
Issued at 154 PM MST Thu Dec 8 2016

Deep cyclonic flow continues across the eastern two thirds of the
CONUS. Arctic high pressure remains over the region with 1045mb
center stretching across the MT/ND border into western/central SD.
Temps today have risen into the single digits to lower teens.
Tonight...temps will again drop especially this evening as
radiational cooling increases with light winds and mostly clear
skies. Lows will drop below zero again across most areas. As the
center of the surface high slides eastward...return flow will set up
across the CWA late tonight into Friday morning. Models are showing
weak overrunning developing primarily across southwest SD late
tonight as the frontal boundary slides back northward...then this
low level forcing will shift into central SD through the mid to late
morning hours. This may bring light snow to these parts of the area
but any accumulations will be minimal. Highs Friday will again reach
the single digits north of the front across northwest SD...and teens
to lower 20s across northeast WY and western SD along the Nebraska
border. Upper flow will become zonal Fri night as a series of waves
cross the region. Upper forcing along with isentropic lift along the
baroclinic zone will bring increasing chances of light snow mainly
across western SD. The timing of this snow will be more toward
late Friday night into Saturday.

.LONG TERM...(Saturday Through Thursday)
Issued at 154 PM MST Thu Dec 8 2016

Fast moving shortwave crosses the area Saturday. Best isentropic
lift moves east of the forecast area Saturday morning. Arctic
boundary shifts northward slightly for the weekend. Warmest
temperature will be for higher elevations of the Black Hills and
areas of southwest South Dakota with lack of snow cover. Second
shortwave crosses the area Sunday which will bring small chances
of snow. Next surge of arctic air will arrive on Monday, will
falling daytime temperatures. Cold temperatures expected for the
remainder of the week, with increasing chance for snow for the end
of the week.


.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1025 PM MST Thu Dec 8 2016

Starting to see high clouds and moisture move into the region at
this hour as weak weather system approaches. Light snow showers
could start as early as 9z across Southwestern SD before moving
eastward toward Central SD late Friday morning. IFR/MVFR cigs
possible across Western SD and Northeastern WY after 9z through
late morning.




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