Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 172043

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
243 PM MDT Mon Apr 17 2017

.SHORT TERM...(This Evening Through Tuesday Night)
Issued at 242 PM MDT Mon Apr 17 2017

Upper ridging across the region is giving way to a strong
shortwave cross the northern Rockies into central MT. A secondary
weak shortwave is pushing across northeast WY and approaching the
Black Hills. This secondary wave is bringing clouds to the area at
this time. Deep southerly low level flow continues across the CWA
with temperatures reaching into the 50s and 60s. Instability
across the Nebraska panhandle is sliding northward into southwest
SD. Models are showing SBCape values reaching 1500 j/kg over the
panhandle which will slide northward into southwest SD over the
next couple hours. The HRRR is showing storm development
associated with the weaker wave initiating in the late afternoon
hours over parts of northeast WY...then sliding eastward over the
southern Black Hills into southwest SD. There is enough shear for
one or two supercells to develop. The toughest hinderance to
storms will be the cap in place...but could see a few storms break
through as the wave crosses the area. Storms will move E/NE into
central SD this evening while a secondary area of showers develops
just ahead of the main wave across northwest SD and a surface
cool front pushing through. Upper ridging and dry weather will
return Tuesday behind the departing wave. Highs will be in the 60s
to low 70s...with the warmest spots across south central SD. A
broad upper trough will push into the western CONUS with a strong
upper wave across the Great Basin. This system will bring
increasing clouds late Tuesday...and chances for precip late
Tuesday night.

.LONG TERM...(Wednesday Through Monday)
Issued at 242 PM MDT Mon Apr 17 2017

Rain and showers will continue on Wednesday, with decent precip
amounts expected in some areas by the time the system exits
Wednesday evening. Models continue to show QPF amounts of close to
an inch or more. The 12z GFS shows some parts north of the Black
Hills reaching close to 2 inches. Some snow accumulation is
possible across the highest elevations of the Black Hills
Wednesday morning, but this would likely be limited to the highest
elevations where up to two or three inches of accumulation are
possible. Cool conditions on Wednesday, with highs in the 40s and
lower 50s. A brief break from pcpn is expected on Thursday before
the next system digs southeast from the Northern Rockies to the
Central Plains Thursday night and Friday. Models have continued
the northward trend. This system will bring rain to the
area...though the higher Black Hills could see another inch or two
of snow. Drier weather is then expected for the weekend as an
upper ridge builds across the region.


.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1115 AM MDT Mon Apr 17 2017

Gusty south/southeast winds over nern WY and far wrn SD will
continue to spread east this afternoon. Winds will then shift to
the west/northwest this evening as a cold front moves through.
Areas of MVFR cigs over swrn SD this morning will slowly lift to
VFR this afternoon. Showers and thunderstorms will move from west
to east across the area this afternoon into tonight along the cold
front. Local IFR conditions expected with the thunderstorms.




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