Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 120512
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1012 PM MST Sun Feb 11 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 300 PM MST Sun Feb 11 2018

Current surface analysis shows next arctic front sagging
southward across western SD and northeast WY this afternoon. Upper
level analysis shows northwesterly flow across the region, with
strong jet across the Northern Plains. One shortwave system is
noted over the Pacific NW, while another is located over the
Canadian Rockies, moving southeast into MT. Skies are variably
cloudy, with the most clouds over northwest SD. A few areas of
light snow or flurries are noted over far northwest SD. Temps
range from the lower teens over northwest SD to the upper 20s over
parts of northeast WY and southwest SD. Winds are northerly
behind the front, westerly or light and variable ahead of it over
southern SD.

Arctic air will slide back into the area tonight as front continues
to slide south of the area late this afternoon and early evening.
Lows tonight will be near or below zero across the area, with wind
chills as lows as 20 below to 25 below over parts of northwest SD.
The shortwave moving into MT now will slide southeast into our
region later this evening and overnight, bringing some light
snowfall to much of the area into Monday, especially across far
northeast WY, the northern Black Hills area, and parts of northwest
and west central SD. Upslope east to northeast low level flow will
also help to wring out what moisture is available. Snowfall amounts
later tonight into Monday will mostly be in the one to two inch
range across much of the earlier mentioned areas, with 3 inches or
so a possibility for some locations from the northern Black Hills
area to far northeast WY. Highs on Monday will mostly be in the 5 to
15 degree range. Another band of light snow could develop late
Monday into Monday evening over southwest SD and track quickly east-
northeast into south central SD, with accumulations up to an inch
possible in those areas.

Medium range models are in good agreement that the arctic air will
only be here for a brief time as much milder air builds in for the
middle of the week. Highs by Wednesday will mostly be in the 40s.
The next chance for pcpn is likely to come Wednesday night into
Thursday as colder air returns. Some light snow accumulations are
possible again, especially from northeast WY to the Black Hills.
There is still inconsistency between the models on how much cold air
will build in and for how long late in the week. 12Z GFS only keeps
the coldest air in through Thursday night while the EC holds it in
through Friday.

Up and down temperature pattern will continue through the weekend as
more seasonable temperatures likely return for Saturday and possibly
Sunday. However, much colder air could return again by the end of
the weekend or early the next week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1009 PM MST Sun Feb 11 2018

Areas of IFR conditions will develop during the rest of the night
mainly over northeastern Wyoming, the Black Hills area and
southwestern South Dakota continuing into Monday afternoon as
light snow spreads across the region. Local LIFR conditions
possible near the Black Hills and far southwestern South Dakota
through Monday morning.

&&

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

$$

DISCUSSION...26
AVIATION...10



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