Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 162201
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
301 PM MST Sat Dec 16 2017

.DISCUSSION...(This Evening Through Saturday)
Issued at 300 PM MST Sat Dec 16 2017

Current surface analysis shows low pressure over northern IA,
with cold front well south and east of the area at this time.
Upper level analysis shows shortwave trough over the Northern
Rockies, with jet streak ahead of it across the Northern Plains.
Jet energy is helping to produce light pcpn, mostly snowfall
across northeast Wyoming and the Black Hills. Drier air at the
lower levels to the north and east is helping to keep the rest of
the area mainly dry. Accumulations so far have generally been in
the 1 to 2 inch range over much of the Black Hills and at least
southern portions of northeast WY. Temps are in the upper 20s and
30s, with some lower 40s over south central SD. Winds are
northerly at 10 to 20 mph in most areas.

Light snow will continue into the evening over northeast WY and
southwest SD, tapering off overnight from north to south as the
trough digs further southwest of the region. Additional
accumulations will mostly be an inch or less, with up to 2 inches
possible over southern Campbell County. Lows will be in the upper
teens and 20s. Sunday will be seasonable with decreasing clouds.
Highs will be in the 30s.

Milder air will push back into the area for Monday and the first
half of next week as ridge rebuilds over the Rockies and eventually
moves into the Plains. Highs will mostly be in the 40s and lower 50s
each day, with Monday looking to be the warmest day. Mainly dry
weather is expected through this period, with breezy conditions on
Monday as the warmer air pushes in.

A significant change in the weather pattern will then take place for
the second half of the week and likely persist through the holiday
weekend. Large upper trough will sink south out of western Canada
late Wednesday and Wednesday night, dragging a strong Canadian cold
front across the area. Temperatures will drop below average for
Thursday and the rest of the week. The initial front will likely
bring strong gusty winds and a period of snowfall Wednesday night
into Thursday. Additional weak disturbances could bring some light
snow/flurries at the end of the week. Looking ahead toward Christmas
Eve and Christmas Day, temperatures are likely to stay below
average, with the possibility of a reinforcing shot of colder air
bringing bitter cold temps by Christmas Day.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1046 AM MST Sat Dec 16 2017

IFR (local LIFR) conditions due to low stratus and -SN will
persist through evening around the Black Hills and west. Expect
MVFR conds east of the Black Hills with areas of IFR conds in
snow. Mainly VFR to high end MVFR can be expected over the NE
third. IFR to MVFR conds will linger through the night SW third,
esp around the Black Hills, with some improvement NE-SW as drier
air works into the region.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Winter Weather Advisory until midnight MST tonight for WYZ055.

&&

$$

DISCUSSION...26
AVIATION...JC


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