Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 102056

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
156 PM MST Tue Jan 10 2017

.SHORT TERM...(This Evening Through Wednesday Night)
Issued at 153 PM MST Tue Jan 10 2017

20z surface analysis had arctic boundary from western MT into
northeast WY into central NE. Low pressure was located along
boundary in northeast WY. Arctic air oozing south as 1015mb high
scoots in from the north. Baroclinic zone along arctic boundary
main concern this forecast period.

Tonight and Wednesday morning, upper trough off the west coast spins
a shortwave from the Rockies into the northern Plains. Arctic
boundary will shift south as 1025mb high moves in from Canada as
westerly flow develops aloft over arctic air. Band of low level
frontogenesis and lift near 130kt jet streak will result in a band
of -SN moving from north to south tonight. Accumulations on the
Plains will be on the light side - around an inch or less. Froude
numbers become favorable for weak upslope enhancement later
tonight and early Wednesday, with 1-2 inches possible for the
Black Hills. Wind chills drop to -25F in the far north late
tonight and Wednesday morning, so will hoist wind chill advisory.

Wednesday afternoon and night, 1028mb arctic high pushes into the
northern Plains with weak isentropic upglide continuing. It will be
slightly enhanced in the late afternoon and early evening hours as
tail end of shortwave whips through the Dakotas from upper low in
south central Canada. Light accumulations possible on the Plains
again with weak upslope enhancement over the Black Hills. Wind chill
headlines will be needed Wednesday night, but will let later
packages determine locations.

.LONG TERM...(Thursday Through Tuesday)
Issued at 153 PM MST Tue Jan 10 2017

Another cold day is expected Thursday. Wind chills Thursday
morning will be in the teens and 20s below zero, with high
temperatures in the single digits and teens. By Friday, weak upper
ridging will develop over the northwestern CONUS, and the Canadian
low pressure systems will shift eastward, along with the arctic
airmass. This will initiate a gradual warming trend through early
next week, with temperatures returning to near average values (mid
30s) Sunday into Monday. Dry weather is also expected through the
weekend. An upper low will track under the ridge across the
central plains on Monday. EC is the only long term model that has
any precip as far north as southern SD, so only went with very
small chances across far south central SD on Monday.


.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 153 PM MST Tue Jan 10 2017

MVFR/IFR ceilings will persist across the South Dakota plains
through the late afternoon. MVFR/IFR conditions with light snow
will develop across the area this evening...with IFR/LIFR
conditions with snow expected after midnight. These conditions
will persist across SD through Wednesday morning. Some improvement
to MVFR conditions may occur across Northeast WY by Wednesday


SD...Wind Chill Advisory from midnight tonight to noon MST Wednesday
     for SDZ001-002.



SHORT TERM...Helgeson
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