Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 202321
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
521 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 00Z TAFS Through 00Z Saturday Evening)
Issued At 521 PM MDT Fri Apr 20 2018

MVFR cigs will overspread western SD and portions of northeast WY
through the evening hours as moist southeasterly flow and SHRA
continue. Upslope flow along the southern and eastern periphery
of the Black Hills will likely lead to IFR cigs later tonight in
these areas, including at KRAP. IFR to occasional LIFR conditions
are expected in higher elevations of the Black Hills, where SHSN
are possible through much of the night. Across portions of
northeastern WY, including at KGCC, prevailing conditions may
actually remain VFR tonight, with better moisture and the majority
of SHRA remaining to their south and east.

On Saturday, MVFR cigs will linger over the Black Hills and far
southern SD as an upper-level disturbance gradually moves
eastward away from the area. Elsewhere, VFR conditions are
expected by Saturday afternoon.

&&

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

$$

DISCUSSION...Pojorlie
AVIATION...Sherburn



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