Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 201958
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
158 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
most.

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 18Z TAFS Through 18Z Saturday)
Issued At 1106 AM MDT Fri Apr 20 2018

Moist southeast flow will bring lowering clouds through tonight as
a storm system passes to our south. MVFR CIGS will push into
southern portions of the area by 21z and then struggle to push
north into far northwest SD. IFR CIGS will develop across
southwest SD/Black Hills this evening. -SHRA will occur through
tonight across southern portions of the area and then east of the
Black Hills Saturday; some -SHSN over the higher Black Hills.

&&

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

$$

DISCUSSION...Pojorlie
AVIATION...Helgeson



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