Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 192335
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
435 PM MST Sat Jan 19 2019

.DISCUSSION...(This Evening Through Saturday)
Issued at 210 PM MST Sat Jan 19 2019

Current surface map places 1038mb arctic high near Lake Winnipeg,
with high pressure extending southward into the eastern Dakotas.
Return flow on the back side of the high keeping temperatures in
the teens across the plains of western South Dakota, with
temperatures into the lower 40s in the higher elevation of the
Black Hills. Northwest flow aloft tonight, with shortwave
tracking through eastern Montana/North Dakota. This may bring some
spotty light snow to portions of northeast Wyoming into the
northern Black Hills tonight/early Sunday.

Upper level ridge builds across the Northern Plains Sunday...with
a period of moist 850-700mb isentropic lift over far northwest
South Dakota Sunday night. Warm nose approaches 0C Sunday night
across northwest South Dakota after best lift shifts north and
east of the forecast area...so not expecting any freezing rain.
However, if sufficient low level moisture lingers there may be a
small threat of freezing fog/freezing drizzle.

Models in decent agreement with upper trof crossing the Great
Basin and Central Rockies Monday...with mid level low briefly
closing off over the central plains Tuesday morning. Best forcing
sets up across northeast Wyoming/far western South Dakota Monday
afternoon...then shifts into south central South Dakota Monday
night. With best lift behind cold front/inverted trof, thermal
profiles suggest most of the precipitation will fall as snow.
Several inches of snow likely along and south of I-90. Favorable
conditions for upslope enhancement late Monday afternoon through
Tuesday morning could result in some 4-6" snow amounts for the
northern Black Hills...with locally higher amounts possible in the
Four Corners-Cheyenne Crossing area.

For the last half of the week into next weekend, global models
continue to show strong Hudson Bay low, with arctic air spilling
into the Upper Midwest and Great Lakes. Very low confidence in
temperatures and snowfall potential across the forecast area due
to run to run consistency and timing with the westward extent of
the arctic air. Ensemble members showing 25-35F spread in high
temperature forecast for Thursday and beyond.

&&

.AVIATION...For the 00Z TAFS Through 00Z Sunday Evening
Issued At 426 PM MST Sat Jan 19 2019

Mid-level VFR cigs will spread across the area tonight as upper
system crosses MT into ND. Some MVFR cigs/vsbys may occur w/ light
snow over the Black Hills and nern WY late tonight into Sunday
morning. Cigs will lower along the ern Black Hills Sunday as
southeast upslope winds develop ahead of stationary front across
ern WY, where winds will be mainly southwest.

&&

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

$$

DISCUSSION...7
AVIATION...55



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