Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 172040

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
240 PM MDT Wed May 17 2017

.DISCUSSION...(This Evening Through Wednesday)
Issued at 232 PM MDT Wed May 17 2017

Upper level analysis has one low spinning over central
KS, and another over ID. Skies are mostly cloudy across the northern
plains. Showers continue over south central SD, and a line of
thunderstorms has moved into northeastern WY. At the surface,
lows sit over central WY and eastern NE. Winds across the CWA are
northeasterly around 10-15 kts. Temperatures are in the 50s.

Some strong afternoon thunderstorms within the northeastern WY
line may be supported by MUCAPE of 500-1000 J/kg and 0-6 km shear
around 30 kts, but CAPE and shear diminish during the late
afternoon hours.

As the central plains low shifts northeastward into MN tonight,
precip will end across central SD. Showers will continue across
northeastern WY, the Black Hills, and southwestern SD. Rain will
change to snow across the higher elevations of the Black Hills, but
accumulations tonight will be minimal. Lows will range from the
lower 30s in the Hills to the lower 40s across south central SD.
Some mid 30s and decreasing cloud cover across northwestern SD may
result in a little patchy frost there, so added mention in grids.

On Thursday, western low pressure system will shift into CO. Showers
will spread across mainly the southwestern half of the CWA, but
thunderstorms are not expected. Highs will be in the 40s and 50s. As
cooler air wraps into the region Thursday night, lows will dip into
the lower 30s across northeastern WY and the Black Hills, and the
continuing precipitation will mix with and change to snow. Models
are actually showing snow beginning as early as Thursday
morning/afternoon, but temps should be warm enough to remain rain
during the day. Accumulating snow is expected across northeastern WY
and the Black Hills late Thursday night and into Friday morning.
Currently thinking the models are overestimating snowfall amounts,
and going with generally 1-3 inches, with locally higher amounts
possible in the higher elevations of the Black Hills. Latest SREF
snow probability supports this, showing 60% chance of greater than 1
inch and 20% chance of greater than 4 inches in the Hills.

Precip will continue Friday as the upper low shifts into the
northern plains, and then will gradually diminish on Saturday.
Upper flow will become northwesterly for the weekend, with mainly
dry weather and warmer temperatures. Chances for showers and
thunderstorms return early next week.


.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1132 AM MDT Wed May 17 2017

Widespread MVFR/IFR ceilings will persist this morning, with some
LIFR conditions around the Black Hills. Lower flight conditions
will continue through today and Wednesday as showers and isolated
thunderstorms continue to affect the area.




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