Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 212007

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

.DISCUSSION...(This Evening Through Saturday)
Issued at 200 PM MDT Sat Apr 21 2018

The upper low is continuing its slow trek eastward, currently
centered over western KS. Weak ridging is moving over the Rockies
and northern plains regions, while the next wave to affect the
area is over the Pacific Northwest. Showers and low clouds
continue to gradually dissipate, and temperatures are rising into
the 50s.

Weak upper ridging between systems will allow for a mild and dry
Sunday. Under mostly sunny skies, winds will be light and variable,
and highs will be in the 60s.

The Pac NW wave will strengthen as it approaches the northern plains
Monday. Models are starting to come into better agreement on this
system, but there are still some distinct differences. The GFS is
the outlier in its more northerly storm track; the Canadian, ECMWF,
and NAM show the 700 mb low sliding through northeastern WY and
southwestern SD, into Nebraska. Therefore, highest amounts of
forecast QPF have shifted southward a bit, and with plenty of
available moisture, some places could receive around an inch of
moisture. Also with the more southerly track, colder air being
pulled into the region will result in more snowfall across
northeastern WY and the Black Hills. The NAM has the most intense
solution of these models, showing quite a bit of snow for the
northern Hills. Current forecast shows 3-5 inches possible across
northeastern WY, and up to 8 inches in the northern Hills. Strong
pressure rises will occur over the region late Monday, resulting
in gusty northwesterly winds, mainly in the evening and overnight.
Models are in better agreement about a slower exit of this
system, showing precip lingering into Tuesday afternoon, but the
ECMWF remains the slowest.

Cool air will linger into Tuesday, with below average highs
expected. The rest of the week will be generally mild and dry,
although another cold front will bring breezy winds and cooler
temperatures for Thursday.


.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1107 AM MDT Sat Apr 21 2018

MVFR/IFR CIGS across parts of northeast WY into southwest/south
central SD will slowly improve through this evening with mainly
VFR conditions prevailing after 06z. Local IFR VSBYS near the
Black Hills toward the SD/NE border will lift by late afternoon.
Elsewhere across northeast WY/northwest SD VFR conditions expected
through the period.




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