Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 120423
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1023 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 06Z TAFS Through 06Z Saturday Night)
Issued At 1021 PM MDT Fri Aug 11 2017

Mainly VFR conds in the period. A few thunderstorms are possible
across the far north and east tonight. There may be some patchy
fog in the early morning on the plains. 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.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...13
AVIATION...JC



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