Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 212012

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
112 PM MST Tue Nov 21 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 111 PM MST Tue Nov 21 2017

Upper level flow will remain amplified, but progressive in the
period, bringing unseasonably warm weather with periodic ridge
topping/flattening impulses in the flow. Staunch WAA ongoing and
will intensify tonight as fast moving lead impulse progresses
through the region Wed. This system will support a mild but breezy
day Wed, with temps in the 50s and 60s, possibly near 70 east of
the Black Hills. Gusty NW winds can be expected on the NW SD
plains. Have increased winds, but remained in the 50 percentile
per numbers, with even breezier conds possible there. WAA will re-
initiate quickly behind Wed/s system with very warm air moving in
aloft. This will support very warm conds Thur, esp on the plains
east of the Black Hills, where record temps will be possible at
downtown Rapid and the airport. Current records at Downtown Rapid
City and at KRAP are 67 and 69 respectively, with current forecast
numbers above those values. Vigorous mid level impulse will push
into the region Thur night int Fri, supporting a cold front and
some precip chances over the western 1/3. Adv to warning wind
speeds will be possible across much of the SD plains Friday given
linked flow and expected decent mixing in a CAA regime. Beyond
Friday, mild weather will continue as another period of WAA and
ridging can be expected into early next week before an expected
longwave trough pushes into the region, supporting rain/snow
chances and a cool down mid next week. ECMWF/GFS/CMC are in pretty
good agreement with the large scale pattern by mid next week, the
differences lie in the low level details per sfc low development,
which continues to differ with each model run with MSLP GEFS
ensemble spread remaining quite high.


.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 952 AM MST Tue Nov 21 2017

MVFR CIGS will continue to dissipate early this afternoon as
drier air moves into the area. VFR conditions are then expected
through the rest of the forecast period.




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