Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 151735

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1035 AM MST Fri Dec 15 2017

.DISCUSSION...(Today Through Thursday)
Issued at 322 AM MST Fri Dec 15 2017

Upper ridging continues across the far western CONUS into the
eastern Pacific Ocean. Cyclonic flow remains over the eastern half
of the CONUS with northwest flow over the northern plains. Generally
quiet weather is expected today with highs in the 50s. Wouldn`t be
surprised if some locations east of the Black Hills pushed just into
the low 60s. Northwest winds of 10-20 kt also expected...the
windiest parts over NW SD. An upper wave will slowly cross the
western CONUS through Saturday...and northern plains Sunday. Colder
air will push into the area Saturday also bringing chances for
mostly snow to the CWA. Best chances for accumulating snow will be
across the Black Hills and northeast Wyoming with 1 to 3 inches by
end of the day Saturday. Highs will be in the 30s to low 40s. Some
lingering light snow will be possible across southwest to south
central SD heading into Sunday. Otherwise drier weather is expected
Sunday as the main trough axis crosses the CWA. Highs Sunday will be
in the 30s to near 40. Warm air advection will return Sunday night
bringing a slightly warmer pattern through Wednesday, with highs in
the upper 30s to upper 40s. Generally dry weather is expected
through the first half of next week. A big change in the pattern is
expected toward the end of the week as a trough sets of over the
western to central CONUS. Much colder temperatures are
expected...likely below average. Chances for snow are also expected
with some possible accumulations.


.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1035 AM MST Fri Dec 15 2017

VFR conditions are expected to continue across the area through
tonight. The main concern this afternoon will be a period of
gusts up to 20-25 kt at TAF sites. There may be a brief period of
LLWS approaching 30 kt at RAP early this evening as nocturnal
cooling begins, but do not have enough confidence to include at
this time.

Conditions will deteriorate late overnight as a clipper
system approaches the area. MVFR CIGS/IFR VSBYS are expected as
light snow overspreads NE WY/W SD. Occasional, localized LIFR
conditions are likely in the 12-18z period, but will hold off on
specific timing until we get closer to the event and confidence




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