Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 112331

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
531 PM MDT Fri Aug 11 2017

.DISCUSSION...(This Evening Through Friday)
Issued at 135 PM MDT Fri Aug 11 2017

Upper trough continues across the eastern half of the CONUS...while
ridging remains over the west coast. A series of shortwaves are
pushing southeast across the northern High Plains...all the way into
Canada. This will allow for active weather over the next couple
days. Storms have quickly developed over the last hour across
northeast WY and the Black Hills area. Models continue to show
relatively weak CAPE of 800-1200 J/KG and decent shear. A few storms
could end up severe...but generally most storms are expected to be
weak to moderately strong with small hail and gusty winds. HRRR
shows the developing line of storms moving eastward over the next 6
hours crossing the Black Hills area...then pushing into central SD
through the evening.

Surface high pressure across the MS Valley will keep south/east flow
across the area Saturday as a shortwave crosses the region. A
surface trough will straddle the CWA through the day with the best
instability across southwest to south central SD. MLCAPE of 1500-
2500 J/KG is expected with decent...but not great...shear. It will
enough for some storms to become strong to severe Monday afternoon
and evening. Highs will be in the 70s to low 80s. Upper wave will
push east of the area Sunday with drier weather expected. The ridge
axis will cross the northern plains Monday morning with southwest
flow developing by Monday evening. Another round of storms are
possible Monday evening with some severe storms possible as a strong
upper wave crosses the region along with a surface trough. Daily
chances for storms are expected next week as a broad upper trough
slowly crosses the region.


.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 526 PM MDT Fri Aug 11 2017

A broken line of thunderstorms will continue to shift east across
the southeast third this evening. Gusts to 45 knots will be
possible with these storms. Other isolated TS are possible across
NW SD this evening, with large hail and gusts over 45 knots
possible there. Local IFR conditions are possible with the
thunderstorms. There may be some patchy fog in the early morning
adjacent to the Hills. Otherwise, TS will develop once again
across western SD, esp scentral SD Sat afternoon. A few strong to
severe storms will be possible as well as local MVFR/IFR conds.




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