Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201116

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
516 AM MDT Sun Aug 20 2017

.DISCUSSION...(Today Through Saturday)
Issued at 203 AM MDT Sun Aug 20 2017

A weak upper wave pushing through MT is creating some
showers and thunderstorms across northwestern SD and far
northeastern WY. At the surface, high pressure is moving into the
northern plains behind the cold front, and a low sits over central
SD. Winds across the northwestern 2/3 of the CWA are northerly
around 10 kts, with southerly winds across south central SD.
Temperatures are falling into the 60s.

Showers and thunderstorms will gradually dissipate and move out of
the CWA this morning. As the surface high slides through ND,
east/southeast winds will become a little breezy. Models continue to
show less CAPE across the CWA, as well as plenty of CIN, although
there could be a few storms that clip south central SD this
evening. Low-level jet ahead of an approaching trough will result
in increased instability across northeastern WY and portions of
western SD overnight, and the cap may weaken enough across
northwestern SD for a few thunderstorms to develop; however, CAMs
are not in agreement about that. Shear around 50 kts could support
an isolated severe storm. Highs today will be in the 80s, with
lows tonight in the upper 50s.

Overnight showers and thunderstorms may continue into Monday morning
across parts of western SD. The GFS and ECMWF are more excited about
morning precipitation than the Canadian, NAM, and many of the CAMs.
It`s still looking like there will be clouds around during the
eclipse, more so across western SD than northeastern WY. However,
models are hinting at some clearing more than they were yesterday.

Upper ridge will bring warm and dry weather for Tuesday and
Wednesday, with highs in the 80s. Chances for precipitation will
return towards the end of the week, as a trough begins to break down
the ridge and places the area in more active southwest flow.


.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 514 AM MDT Sun Aug 20 2017

Isolated showers and thunderstorms will end early this morning
across northwest South Dakota. Additional thunderstorms will
develop late this afternoon, with coverage increasing across
western South Dakota this evening/overnight. MVFR/Local IFR
conditions with the thunderstorms, especially tonight. Otherwise,
VFR conditions expected.




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