Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 201121
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
421 AM MST Tue Feb 20 2018

.DISCUSSION...(Today Through Monday)
Issued at 326 AM MST Tue Feb 20 2018

Current surface analysis shows low pressure now well south and
east of the region, with arctic high pressure over MT. Upper level
analysis shows trough axis now over eastern MT and WY, weakening
and speeding up as it moves into the Plains. KUDX radar shows very
light snowfall and flurries east of the Black Hills moving
eastward, with regional radars showing heavier snowfall over north
central NE into portions of far south central SD. Have cancelled
warnings for everywhere except Todd and Tripp Counties, but snow
should taper off and end there over the next couple of hours.
Skies are still mainly cloudy across the area, though some breaks
in the clouds have started to move into northeast WY. Temps are
near or below zero across the area, coldest over northeast WY
where some areas are around 15 below. Wind chills range from 10
below to 30 below zero, lowest over southern portions of northeast
WY. Will issue a wind chill advisory for southern Campbell and
Weston Counties for early this morning.

The forecast looks relatively quiet for the rest of the week, though
it will remain bitter cold through midweek as arctic high pressure
slowly passes over and eventually east of the area. Clouds will
gradually decrease from west to east today, with lingering snow
exiting far eastern portions of the CWA by mid morning. High
temperatures will mostly be in the single digits with wind chills
remaining near or below zero. Mostly clear skies, light winds, and
fresh snowcover tonight will allow temps to drop well below zero in
most areas. Some favored locations will likely be in the 20s below.
Wind chill headlines will be needed for at least portions of the
area. Will let dayshift have a final look at where they will be
needed. Wednesday will be a bit milder, but still well below
average, teens to mid 20s.

Below average temperatures will persist through at least Friday. A
large scale trough will dig south across the western state mid to
late week, with southwesterly flow aloft developing from the Four
Corners region to the Plains. A shortwave will eject out of the
trough and cross the Central Plains on Thursday. Some snow could
clip south central SD, with light accumulations possible. Otherwise,
mainly dry weather is looking likely through the weekend. Flow aloft
will become northwesterly again over the weekend and a weak
disturbance or two could bring a few snow showers to mainly
northeast WY and the Black Hills late in the weekend or early next
week. Temperatures will likely get back closer to average levels
over the weekend, but significant snowcover in many areas should
limit warming potential.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 419 AM MST Tue Feb 20 2018

MVFR to localized IFR conditions in light snow across parts of
western and central SD will gradually become VFR by late morning.
VFR conditions expected through the period across northeastern WY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning until 9 AM CST this morning for SDZ047-049.

WY...Wind Chill Advisory until 9 AM MST this morning for WYZ055-058.

&&

$$

DISCUSSION...26
AVIATION...Johnson



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