Area Forecast Discussion
Issued by NWS Rapid City, SD

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646
FXUS63 KUNR 211121
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
521 AM MDT Sat Apr 21 2018

.DISCUSSION...(Today Through Friday)
Issued at 353 AM MDT Sat Apr 21 2018

Upper level analysis has slow moving closed low over southeast
Colorado, pushing bands of clouds northward into southern South
Dakota. Very light precip is occurring in these bands across the
southern South Dakota plains. At the surface, weak high pressure
is in place across the eastern Dakotas, with weak lee trough
across central Montana. Temperatures at 4am are in the 30s to
lower 40s, with southerly winds of 10 to 20 mph.

Upper low will continue to slowly shift east under the broader
ridge across the central CONUS. Chances for very light rain will
persist across southern South Dakota for much of the day. Highs
will warm into the 50s to lower 60s, warmest in northern and
western areas where cloud cover should start to break up by late
afternoon. Precip should wain by late afternoon into the evening
with lows tonight in the 30s.

Brief upper ridging will allow for a mild and dry day Sunday, with
highs in the 60s. However, rain returns Monday afternoon as a
shortwave pushes through the region. ECMWF is the slowest of the
medium range models, 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 quarter to half
an inch of rain will be possible across parts of the area, with
models currently indicating northwestern SD and far northeastern
WY will receive the most.

Upper ridging should keep weather mainly dry and mild much of
next week. Models are hinting at a fast-moving Canadian shortwave
diving into the northern plains Wednesday night, likely bringing
some windy conditions to the area, along with some spotty light
precip across northeast Wyoming and the Black Hills.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 516 AM MDT Sat Apr 21 2018

MVFR-IFR CIGS will gradually clear west to east, lingering over
portions of southwestern/south central SD through early afternoon.
Otherwise, VFR conditions are expected most places by afternoon.
IFR-MVFR CIGS may spread back north into scentral SD late
tonight.

&&

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

$$

DISCUSSION...15
AVIATION...JC



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