Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 121730
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1130 AM MDT Sat Aug 12 2017

.DISCUSSION...(Today Through Friday)
Issued at 338 AM MDT Sat Aug 12 2017

Upper level analysis has large trough persisting across the
eastern half of the CONUS...while ridging remains over the west
coast. A strong shortwave in the larger trof is located across
southern Saskatchewan into northeast MT and northern ND. Showers
and thunderstorms associated with this shortwave are ongoing
across MT and ND this morning. At the surface, high pressure is
located across MN with weak low pressure across MT and WY.
Temperatures at 3am across the area are in the 50s, with some 60s
across south central SD. Winds are light out of the south.

Surface high pressure across MN will keep south/east flow across
the area today as the strong upper shortwave to the north swings
into the Dakotas. Weak surface low pressure and associated trough
will shift into western SD by this afternoon, with the best
instability across southwest to south central SD. MLCAPE of 1500-
2500 J/KG is progged with decent shear. It will be enough for
some storms to become strong to severe this afternoon and
evening with large hail and damaging winds. Highs will be in the
70s to low 80s. Stronger storms will shift east through the
evening, with activity ending across most of the area after
midnight. Low temperatures will be in the 50s and lower 60s.

Upper shortwave will push east of the area Sunday with weak
ridging moving into the northern Plains. Another weak impulse will
move through the ridge late in the day, with showers and
thunderstorms possible, mainly across northeast WY and southern
SD. Decent instability and shear will remain across the area, so a
stronger storm or two will still be possible. Highs on Sunday will
be in the upper 70s to mid 80s. Lows Sunday night will be in the
50s.

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 through much
of the week as a broad upper trough slowly crosses the region.
Temperatures will be close to season averages through the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1123 AM MDT Sat Aug 12 2017

Scattered afternoon/evening TSRA expected, mainly over western and
central SD. Local IFR conditions, gusty winds, and isolated
severe storms possible. Some IFR cigs/vsbys may redevelop later
tonight across northwest SD. Across northeast WY, VFR conditions
expected through the period.

&&

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

$$

DISCUSSION...15
AVIATION...Johnson


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