Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 231022

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
322 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 06Z TAFS Through 06Z Friday Night)
Issued At 1017 PM MST Thu Feb 22 2018

In the wake of this evening`s light snow, MVFR/IFR cigs have
developed across portions of the SD plains, particularly along and
east of a line from KD07 to KIEN. These are expected to drift
southeastward out of our area by 10z, allowing VFR conditions to
prevail area-wide through Friday afternoon.

Conditions will begin to deteriorate from south to north across
eastern WY/western NE late in the TAF period as snow overspreads
the region. Associated lowered cigs/vsbys could reach the southern
Black Hills, and potentially even approach our TAF sites, by 06z
tomorrow evening. For now, however, expecting VFR conditions to
prevail through the TAF period at KRAP/KGCC.




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