Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 160525

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1125 PM MDT Fri Sep 15 2017

Issued at 723 PM MDT Fri Sep 15 2017

01z surface analysis had low over southwest MN with cold front
into southeast WY. Water vapour loop had nice upper trough over
AB/SK stretching into the northern Rockies. Main upper low over
southwest MT/northeast ID with several shortwaves of note spinning
around it. One was over northwest ND and another over southern
WY/northern CO. This is the wave that will produce our precipitation
chances overnight, evidenced by IR enhancement/radar returns over
eastern WY into western ND. Still looks like some flakes of snow
over the higher elevations given wet bulb zero profiles.

Forecast updated for these trends: less precipitation coverage
early this evening, but then increasing from southwest to
northeast overnight, especially east of the Black Hills.


.DISCUSSION...(This Evening Through Friday)
Issued at 253 PM MDT Fri Sep 15 2017

Water vapor shows upper trof approaching the Rockies with strong
shortwave lifting through southeast Montana/southwest North
Dakota. Bulk of precipitation lifting north of forecast area with
scattered showers around the Black Hills. A few showers will
linger into tonight as secondary shortwave crosses western South
Dakota. Temperatures marginally cool enough for rain/snow mix in
higher elevations of Black Hills and northeast Wyoming. Upper
trof crosses northern plains Saturday. Steep lapse rates will
result in diurnal trend to showers. High pressure across the area
Saturday night with clearing skies. Frost likely for low lying
areas on the plains.

The models remain in decent agreement next week with another deep
trof moving into the western CONUS.  Shortwave ridging ahead of
the trof will bring warm and dry conditions Monday/Tuesday with
cold front crossing the area Tuesday night. Cooler for the second
half of the week with increasing chances of precipitation.


.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1124 PM MDT Fri Sep 15 2017

SHRA with areas FG/DZ will continue through the forecast period.
A bit of snow may occur over the higher elevations. Isolated TSRA
possible southeast of the Black Hills tonight. Widespread IFR
conditions are expected with local LIFR conditions in/near the
Black Hills and where FG/DZ occurs. Conditions will improve from
west to east Saturday afternoon into the evening hours.




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