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Area forecast discussion for western South Dakota and northeastern Wyoming
National Weather Service Rapid City South Dakota
1022 PM MST Wed Dec 11 2019

issued at 543 PM MST Wed Dec 11 2019

00z surface analysis showed Arctic boundary has slipped a bit
southwest late this afternoon. A look out the window and a call
from the public indicate some patchy fog may be developing on the
north through east foothills areas this evening so have added to
the forecast.


Discussion...(this evening through wednesday)
issued at 230 PM MST Wed Dec 11 2019

Current surface analysis shows nearly stationary frontal boundary
stretching from eastern Montana to the Black Hills area and central
NE. Milder air is in place to the south and west of the boundary,
much colder air to the north and east. Skies are mostly cloudy
across much of the area with temps ranging from the upper teens
over parts of northwest South Dakota to near 40 over southern parts of
northeast Wyoming. Winds are southwesterly to the west of the front,
southeasterly to the east of it.

Fairly active northwesterly flow aloft will persist through the
forecast period. This will result in weak systems moving through
from time to time, with chances for mostly light snow. Temperatures
will bounce around some as we remain in the battle zone of air
masses, Arctic air to the northeast and milder air to the southwest.

For tonight, a weak upper level wave will pass mostly north of the
area. A little light snow could clip far northwest South Dakota and develop
over the northern Black Hills this evening. Any accumulations will
generally be a dusting. Skies will be variably cloudy with lows
mostly in the mid teens to mid 20s. Front will shift a little
further north and east across the area as a warm front on Thursday,
allowing for a warmup across the area Thursday into Friday. Highs
will generally be in the 30s and lower 40s Thursday, with mildest
temps across southern areas on Friday. The next system will move
further south across the region, dragging a cold front across the
area as well, on Friday. Areas of light rain and snow look more
likely, especially in the late morning and afternoon. Snow
accumulations of up to an inch look possible, especially from
northeast Wyoming to the Black Hills and southwest South Dakota. Up to a couple of
inches is possible over the northern Black Hills. Breezy
northwesterly winds will develop behind the front.

Colder air will settle back into most of the area for the weekend,
especially for areas north and east of the Black Hills. Highs on
Saturday will range from the teens north and east of the Black Hills
to around 30 over northeast Wyoming and far southwest South Dakota. Temps should be
a bit higher on Sunday for most areas, but still below average
levels. Another weak upper level system could clip mostly western
and southern parts of the forecast area sometime Saturday into
Saturday night, with a chance for additional light snow.

Looks like ridging will build across the interior of the western US
for at least the first half of next week, if not most of the week.
This will bring mainly dry conditions to the area. The region should
see a gradual warming trend early to mid week, with above average
temps possible by next Wednesday.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1019 PM MST Wed Dec 11 2019

Leftover IFR/MVFR ceilings associated with patchy light snow over
northwest South Dakota will persist overnight, but then move out Thursday
morning. Otherwise, VFR conditions expected across the area.


Unr watches/warnings/advisories...
South Dakota...none.


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