Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 130939
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
239 AM MST Wed Dec 13 2017

.DISCUSSION...(Today Through Tuesday)
Issued at 235 AM MST Wed Dec 13 2017

Upper shortwave is diving south through the northern plains,
along with an 85-kt jet. The cold front has made its way through
the CWA, and skies are clearing behind it. Northwest winds across
the western SD plains are very strong, sustained at 25-40 mph,
with gusts of 50-60 mph. Radar continues to show the smoke plumes
associated with the Legion Lake fire, which stretch into
Nebraska.

Highest pressure rises are progged to be over the CWA between 12 and
18Z today, and so very strong winds will continue through the
morning. The pressure gradient will slacken in the afternoon, and
winds will gradually decrease. Highs today will be in the 40s on the
plains, with 30s for the Black Hills.

Another upper wave will slide through the region tonight into
Thursday. Yet another day of gusty winds is expected, not only
across the western SD plains, but also over northeastern WY. The NAM
forecast soundings are showing 25-35 kt sustained winds possible,
and the GFS is even higher, especially for the Rapid City area.
Pressure rises and 850 mb winds don`t look quite as strong as today,
though. Thinking it will be more of a Wind Advisory event, but would
not be surprised if there were a couple 60 mph gusts.

More moisture will be associated with this wave, and light snow is
expected across much of the CWA. Less than an inch of snow
accumulation is in the forecast for the plains, but the northern
Hills could see a few inches. Froude number ramps up between 09-12Z
as the winds increase. GFS and ECWMF are indicating about an inch of
snow possible, while the NAM is the outlier with 10 inches. SREF is
indicating between 1 and 4 inches will be likely, which is what is
currently in the forecast. Falling snow, combined with the strong
winds, will create some areas of blowing snow across the CWA. Highs
Thursday will dip into the 30s.

Warmer and drier air moves back into the region Friday, with highs
in the 50s. Chances for precip increase Friday night into Saturday,
as a stronger wave moves over the Rockies. Another cold front will
cool temperatures to the 30s and 40s for the weekend. Models are
then showing another large upper ridge building over the western
CONUS for early next week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1020 PM MST Tue Dec 12 2017

VFR conditions expected through Wednesday. Strong northwest winds
will spread across the area behind a cold front with gusts of
40-50kt over the South Dakota plains. The winds will diminish
Wednesday afternoon.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 3 PM MST /4 PM CST/ this afternoon for
     SDZ042>044-046-047-049.

     Wind Advisory until 3 PM MST this afternoon for SDZ001-002-
     012>014-025-030-032-074.

     High Wind Warning until noon MST today for SDZ026-031-072-073.

     Wind Advisory from noon today to 3 PM MST this afternoon for
     SDZ026-031-072-073.

WY...None.
&&

$$

DISCUSSION...Pojorlie
AVIATION...7



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