Area Forecast Discussion
Issued by NWS Rapid City, SD

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713
FXUS63 KUNR 222333
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
433 PM MST Sun Jan 22 2017

.SHORT TERM...(This Evening Through Monday Night)
Issued at 158 PM MST Sun Jan 22 2017

Deep upper low will fracture and eject toward the region in the
period, supporting cyclogenesis over the central plains and
increasing chances for accumulating snow across the region.
Forecast models continue to struggle with the details of this
system given a fracturing wave and tendencies to close an upper
low over the northern plains, not to mention the track of this
potential closing upper low. This then leads to a whole set of
issues WRT moisture transport, FGEN band location, and potential
CSI banding given potential instability indicated in model
forecast soundings. The most probable scenario was trended to in
the forecast database, one where SW-Central SD sees warning snows
in addition to the northern Black Hills, with general adv amounts
or less elsewhere, esp in the lee of the Black Hills if NW h7
winds materialize early. At this point feel confident to issue a
winter storm watch from the BH, SE. CAA/Pressure falls associated
with cyclogenesis will support breezy/gusty winds on the SD plain
Tues, further supporting a lean toward a watch.

Brief WAA surge may support some light snow over the western BH
tonight spreading NE onto the NW SD plains Monday morning. Any
precip may mix or fall as rain Monday morning, albeit very light.
Patchy fog can be expected over NW SD into scentral SD tonight.
There are a few model members indicating the potential for some
light freezing drizzle there, late tonight into the Monday
morning. However, confidence in this remains low. FGEN zone will
setup over the far NW Monday and may support periods of light snow
there Monday afternoon and evening. Main wave and pos theta-e
surge snows will arrive late Monday night and continue into Tues,
tapering off NW-SE Tues evening. Upslope enhancement can be
expected in the northern BH Tues, offering decent snow rates there
at times Tues. Current forecast thoughts are for 6+ inches in the
northern Black Hills and scentral SD, with 2-5 inches elsewhere.
Locally higher amounts will be possible if FGEN banding develops
and persists.

.LONG TERM...(Tuesday Through Sunday)
Issued at 158 PM MST Sun Jan 22 2017

Upper low lifts into the Great Lakes region on Wednesday with
broad trof remaining over the northern CONUS. some residual
flurries will be possible over Northeast WY and the Black Hills,
along with far south central SD for much of the day. Dry weather
is expected for the rest of the extended period with ridging
building across the Northern Plains by the weekend. Temperatures
will gradually warm from the 20s early in the period, to the upper
30s and lower 40s by the weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 428 PM MST Sun Jan 22 2017

Stratus from southeast MT into south central SD will persist
tonight with IFR CIGS/VSBYS. Mainly VFR conditions are expected
over northeast WY and the rest of western SD tonight, but a bit
of -SN may develop with local MVFR conditions late. Mainly VFR
CIGS over the southwest will lower and thicken through the day
Monday with local IFR conditions developing across northeast WY
into northwest SD late in the day. A winter storm will then take
aim on the area Monday night into Tuesday with an array of poor
aviation weather conditions.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from Monday evening through late Tuesday
     night for SDZ024>032-041>044-046-047-049-072>074.

WY...Winter Storm Watch from Monday evening through late Tuesday
     night for WYZ057.

&&

$$

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



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