Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 231714

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1014 AM MST Fri Feb 23 2018

.DISCUSSION...(Today Through Thursday)
Issued at 246 AM MST Fri Feb 23 2018

Current upper level analysis has large positively tilted trof
across the western CONUS with ridging along the East Coast. Within
the trof, at least a couple of shortwaves can be seen via water
vapor imagery. Skies across the northern plains are variably
cloudy, with cloudy skies across eastern SD, and clear skies
across western SD. At the surface, arctic high resides across
much of the area, with temperatures in the single digits either
side of zero at 3am. Winds are out of the northwest.

Large western trof will amplify today as shortwave energy begins
to eject out of the trof across the central Rockies. Arctic
surface high will shift southeast across the Dakotas, with light
southerly return flow beginning across northeast WY and far
western SD during the day. Skies will be mostly sunny today, with
temperatures remaining below average - in the teens to mid 20s.

Upper trof begins to shear out tonight as the arctic surface high
shifts further east. Developing shortwave in the upper trof will
lift northeast into southern SD overnight, bringing a chance of
light snow to that area. Lows will fall into the single digits.

Developing upper shortwave lifts through southern and central SD
on Saturday, with accumulating snowfall likely across south
central SD. Snowfall totals of 1 to 3 inches are expected across
Mellette, Todd, and Tripp counties, with the higher amounts across
Tripp County. Further west across the western SD plains, cloudy
skies and light to no snowfall is expected. Highs on Saturday will
be a bit warmer, in the 20s to lower 30s. System shifts quickly
northeast Saturday night.

Psuedo zonal upper flow takes over for Sunday into next week with
mainly dry conditions expected, and temperatures moderating into
the 30s. A couple of very weak shortwaves may bring some very
light snow to parts of the area on Tuesday, and again on Thursday,
but no appreciable accumulations are expected.


.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1011 AM MST Fri Feb 23 2018

VFR conditions across the CWA should persist through about 03z.
Conditions will begin to deteriorate across southwestern and
central SD late tonight as snow spreads in from the south, with
MVFR/IFR conditions expected. MVFR conditions expected to just
reach KRAP and last until about 16z, but KGCC is expected to
remain VFR through the period.




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