Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 210440

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1040 PM MDT Fri Apr 20 2018

.DISCUSSION...(This Evening Through Friday)
Issued at 155 PM MDT Fri Apr 20 2018

The upper low spins over the Four Corners region, pushing rain
northward into the northern plains. Radar shows rain expanding
across southern SD. Somewhat tight pressure gradient exists
between the surface high to the east and low to the west, creating
some breezy southerly winds this afternoon. Temperatures are in
the 40s and lower 50s.

Rain will continue tonight, especially across the southern half of
the CWA. Rain will change to snow over the Hills, resulting in an
inch or two of snowfall by Saturday morning. As the low shifts
eastward, precipitation will end Saturday. Skies will remain mostly
cloudy during the day, and highs will be in the 50s.

Brief upper ridging will allow for a mild and dry day Sunday, with
highs in the 60s. However, rain returns Monday as a shortwave pushes
through the region. The Canadian is now aligning more with the ECMWF
and GFS, holding off rain until Monday afternoon. The ECMWF is the
slowest of the three, showing precip lingering into Tuesday
afternoon. Isolated thunderstorms will be possible Monday afternoon
and evening, and then rain will change to snow across northeastern
WY and the Black Hills Monday night. One or two inches of snow will
be possible in those places. A half to three-quarters of an inch of
rain will be possible across parts of the area; models are currently
indicating northwestern SD and far northeastern WY will receive the

Upper ridging should keep weather dry and mild much of next week.
The ECMWF and GFS are hinting at a fast-moving Canadian shortwave
diving into the northern plains Wednesday night, but the forecast
remains dry at this time.


.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1040 PM MDT Fri Apr 20 2018

IFR/LIFR cigs will continue over the Black Hills and near the
eastern/southern foothills overnight, including at KRAP. Higher
elevations will also experience IFR/LIFR vsbys in FG. Surrounding
this area, MVFR cigs are expected over southwestern SD and
portions of northeastern WY. MVFR cigs could temporarily impact
KGCC through about 10z, but VFR conditions should prevail.

MVFR cigs may linger over portions of southwestern/south central
SD through early Saturday afternoon. Otherwise, VFR conditions are
expected across the area after daybreak.




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