Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 141711

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1011 AM MST Sun Jan 14 2018

.DISCUSSION...(Today Through Saturday)
Issued at 234 AM MST Sun Jan 14 2018

One more potent backside impulse and associated jet streak will
advect SE through the region today, supporting more rain/snow
along with one more west push of the arctic front. The persistent
eastern CONUS trough will breakdown early this week, allowing the
western NOAM ridge to shift east and support a warming trend mid
week on.

WAA ongoing ahead of the next jet streak/impulse. SFC low will
shift through the region today with warm westerly flow ahead of
the low supporting temps into the 40s in the lee of the BH, with a
brief respite from arctic air over the rest of the area as temps
rise into the 20s and 30s. Strong lift/sufficient moisture, and
strong ll convergence with the arctic front will support another
band of snow across the region today, shifting SW through evening.
Expect 1-2 inches of snow across much of the plains (away from
downslope areas SE of the BH), with upslope enhancement in the
northern BH. Given thermal profiles suggesting steep LL lapse
rates into the DGZ and strong near saturated flow, expecting 3-5
inches in the northern BH, with locally 6 possible above 6kft.
Will issue a ww adv there. Precip may start as or mix with rain
over the SW third (outside the BH) given warm thermal profiles.
Strong NW winds with the clipper system will support patchy
blowing snow over much of the area when CAA revs up this
afternoon. Snow will end this evening all places as very cold dry
air settles into the region under a building sfc high. Expect lows
below zero tonight most places tonight and esp Monday night with
the sfc ridge over the area. Arctic air combined with NW winds
ahead of the high will support wind chills below -25 on the SD
plains later tonight and again Monday night. Will issue a wind
chill adv for this and make it simple going through the entire
period even though wind chills will rise above criteria Monday
afternoon for a while.

Upper level ridge will shift east after Monday, with WAA Tue
through Thur. Dry weather expected through the work week.
ECMWF/GFS/GEM continue to shift the eastern PAC trough onshore by
Friday. Given progressive flow downstream, this longwave trough
will shift east into the central CONUS toward the weekend,
supporting a sfc cyclone in the central CONUS. The path of this
cyclone will depend on the degree/period of jet streak digging
over the western CONUS. Some precip can be expected over the FA as
the upper trough pushes through the region next weekend. However,
heavier banded precip will be dictated by the path of the
cyclone, which remains unknown attm. Cooler weather can be
expected for next weekend behind this system.


.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1008 AM MST Sun Jan 14 2018

MVFR/IFR conditions will spread across the area this afternoon as
the next round of snow moves through. By 06z the snow will be
mostly southwest of the area, with gradual improvement to VFR
condtions expected after 06z as drier air moves in and snowfall
ends. Otherwise, gusty northwest winds will producing blowing snow
this afternoon and evening across the plains.


SD...Winter Weather Advisory until 11 PM MST this evening for SDZ024-

     Wind Chill Advisory from 11 PM MST /midnight CST/ this evening
     to 11 AM MST /noon CST/ Tuesday for SDZ001-002-012>014-031-

WY...Winter Weather Advisory until 11 PM MST this evening for WYZ057.



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