Area Forecast Discussion
Issued by NWS Rapid City, SD

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450
FXUS63 KUNR 211007
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
407 AM MDT Fri Apr 21 2017

.SHORT TERM...(Today Through Saturday Night)
Issued at 332 AM MDT Fri Apr 21 2017

Upper level analysis has weak ridging across the Northern Plains
with negatively tilted trof crossing the northern and central
Rockies at the moment. At the base of the trof, closed low is
currently crossing the Colorado Rockies. Skies are partly cloudy
across northern SD, and mostly cloudy across Northeastern WY and
southwestern SD. Very patchy fog is also present across
northwestern SD. Some weak radar returns are present along the
southwest edges of the forecast area. At the surface, high
pressure is centered across North Dakota, with surface trof
extending from north central Montana into central Colorado.
Temperatures at 3am are in the mid 30s to mid 40s with light south
to southeast winds.

Today...Clouds will continue to increase from the west today as
the upper level trof and associated surface trof shift into
eastern Montana and Wyoming. Southeast winds will increase through
the day, with breezy conditions expected across parts of Northeast
WY and northwestern SD as the pressure gradient increases between
the departing surface high to the east and approaching surface
trof to the west. Light rain showers will persist across
Northeast WY and spread east into the Black Hills/far southwest SD
by early afternoon. Highs will range from the mid 40s to mid 50s
across northeast WY and the Black Hills to the upper 50s to lower
60s over northwest to central SD.

Tonight...Surface trof stalls out and weakens across the Black
Hills area late tonight as weak upper ridge remains across the
Dakotas. Upper low over Colorado will slide south of the area over
night with just some light showers lingering across far western
and southern portions of the area. Lows tonight will fall into the
30s.

Saturday...Upper ridging remains across the Dakotas on Saturday
with cloudy skies persisting across Northeast WY and southwestern
SD. Temperatures will be a few degrees warmer, with highs in the
50s to mid 60s. Variably cloudy skies will persist into Saturday
night with low temperatures in the 30s to lower 40s.

.LONG TERM...(Sunday Through Thursday)
Issued at 332 AM MDT Fri Apr 21 2017

Upper ridge remains over the area early Sunday with mostly sunny
skies expected. Highs will climb into the 70s across a good
portion of the plains. By Sunday night, the ridge breaks down with
active southwest flow setting up over the area. Weak shortwave
energy in this flow could bring a few showers to the area after
midnight. Lows will fall into the 40s.

Next week looks to be unsettled and on the cool side as the next
series of disturbances cross the region. Daily chances for
showers are expected in most areas, with the best chances of
precipitation on Tuesday and again on Thursday. Colder air later
in the week could bring some overnight/morning snow to some areas
depending on the timing of the systems. High temperatures will be
near average early in the week, dropping below average mid to late
week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1056 PM MDT Thu Apr 20 2017

Scattered rain showers with areas of MVFR ceilings will develop
over northeastern Wyoming and parts of far western South Dakota
late tonight and continue through Friday afternoon. Areas of MVFR/IFR
ceilings are expected over the rest of western South Dakota late
tonight/early Friday as fog and stratus develop. Ceilings will
improve over western South Dakota late Friday morning with VFR
ceilings Friday afternoon. MVFR conditions will persist in northeastern
Wyoming Friday night as rain showers and low clouds linger.

&&

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

$$

SHORT TERM...15
LONG TERM...15
AVIATION...Helgeson



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