Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 152316
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
416 PM MST Mon Jan 15 2018

.DISCUSSION...(This Evening Through Monday)
Issued at 137 PM MST Mon Jan 15 2018

20z surface analysis had arctic high over western ND with
clearing skies over the CWA. Main concern this forecast wind
chills.

Tonight into Tuesday morning, arctic high shifts slowly southeast.
Excellent radiational cooling in place with snow cover over 80%
of the CWA. Northerly winds will subside this evening, but then
pick back up some overnight into Tuesday morning as return
southerly flow. Wind chills will bottom out between -15F and
-35F, so will continue current headlines as well as expanding
slightly northwest into far northeast WY.

Tuesday afternoon into Wednesday, fast moving shortwave trough moves
across south central Canada with associated surface low. This low
will drag a warm front through the CWA as upper level ridge pushes
into the northern Plains. Much warmer temperatures expected.

Thursday/Friday, upper/thermal ridge dominates with temperatures
10-15F above normal.

Later Friday into next weekend, pseudo-split flow develops with
weaker northern stream bringing minor disturbances, some PoPs and
cooler temperatures to the CWA. Main storm track looks to remain
southeast of the CWA evidenced by majority of latest ensemble
data. Temperatures will be tricky with tight low level baroclinic
zone hanging out.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 416 PM MST Mon Jan 15 2018

Lingering MVFR ceilings across southwestern and south central SD
will dissipate after dark, giving way to VFR conditions across the
area through the TAF period. There is potential for a few hours of
gusts 20-25 kt at KGCC Tuesday afternoon. However, have left this
out of the TAF for now, as stout low-level inversion is expected
to limit mixing of stronger winds to surface.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Chill Advisory until 11 AM MST /noon CST/ Tuesday for
     SDZ001-002-012>014-025-031-032-042>044-046-047-049-072-073.

WY...Wind Chill Advisory until 11 AM MST Tuesday for WYZ054-056-071.

&&

$$

DISCUSSION...Helgeson
AVIATION...Sherburn



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