Area Forecast Discussion
Issued by NWS Rapid City, SD

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175
FXUS63 KUNR 181128
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
428 AM MST Thu Jan 18 2018

.DISCUSSION...(Today Through Wednesday)
Issued at 245 AM MST Thu Jan 18 2018

Mild westerly flow across the forecast area this morning, with
temperatures currently in the 20s to mid 30s...some lower 40s in
downslope areas on east side of Black Hills. Upper level ridge
builds across the area today as trof begins moving into Pacific
Northwest. Highs around 20F above average today. Warmest locations
will be from Rapid City into southwest South Dakota with lack of
snow cover. Thick cirrus moving into the area may keep temperatures
from reaching full potential. Gusty southwest winds expected
across the Black Hills and portions of northeast Wyoming tonight.
Another mild day on Friday, though cooler than today as low level
thermal ridge shifts east.

Focus turns to snow event for the weekend with increasing confidence
in accumulating snow. As upper trof moves through the western
CONUS Saturday, forecast area will be in right entrance region of
jet steak from eastern Montana into the Great Lakes.
Frontogenitical forcing along low level baroclinic zone sets up
across east central Wyoming into southwest South Dakota. As the
upper trof moves into the plains Sunday, low cuts off across the
central plains and tracks northeast. Models have been fairly
consistent in showing the large scale setup last two days. Model
QPF/snow totals have been increasing for the Black Hills/southwest
South Dakota over the last several runs, with 06Z NAM/GFS
indicating that snow totals could exceed 8-10 inches. However,
ensemble members show wide spread ranging from 2 to 10 inches. At
this time, snow totals are hard to pin down. Best lift
Saturday/Saturday night will be in a narrow axis so any shift
north/south during the event have big impact on storm totals. Snow
shifts from western South Dakota into south central South Dakota
Sunday as deformation zone develops on back side of upper low.
Current snow amounts in the forecast are near ensemble mean.

Near average temperatures and mainly dry conditions expected for
the first half of next week.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 427 AM MST Thu Jan 18 2018

VFR conditions will continue through the forecast period.
Gusty southwest winds will develop over northeastern Wyoming late
today into tonight.

&&

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

$$

DISCUSSION...7
AVIATION...13



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