Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 221132
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
532 AM MDT Fri Mar 22 2024

.KEY MESSAGES...
222 AM MDT Fri Mar 22 2024

-Winter storm will impact the area this weekend. Highest snowfall
 amounts northwest Dakota into central South Dakota.

-Blizzard conditions possible later Sunday through Monday
 morning, especially on the plains east of the Black Hills into
 central South Dakota.

-Greatest uncertainty in snowfall amounts for parts of
 southwestern South Dakota, including the Rapid City area.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 222 AM MDT Fri Mar 22 2024

Current surface map has cold front dropping through the Central
Plains with cold high pressure extending across Canadian Prairies
into the Northern Plains. Water vapor shows shortwave moving
across eastern South Dakota, with flat ridge across the northern
Rockies. Upper ridge shifts eastward today/tonight. Sufficient
low/mid level moisture and very week upslope flow may be enough
for some light snow showers/flurries today...mainly around the
Black Hills area.

Focus turns to western CONUS trough. Upper flow becomes
southwesterly on Saturday with initial shortwave lifting through
Wyoming into easter Montana. Increasing isentropic
lift/frontogenesis will bring some light snow during the day
Saturday, mainly north and east of the Black Hills. Accumulations
during the day Saturday will generally be an inch or less.
Further south and west, showery precipitation is expected during
the day.

Strong shortwave ejects from the trough this weekend. Surface low
deepens across western Kansas Sunday and lifts into northern
Iowa/southern Minnesota on Monday. Strong lift associated with isentropic
lift/frontogenisis will reside across eastern Montana into
northwest South Dakota/southwest North Dakota Saturday night/early
Sunday, with best forcing shifting into central South Dakota on
Sunday. Well defined deformation zone develops across south
central South Dakota later Sunday into Sunday night. Guidance
still fairly consistent with higher snowfall totals, with 70-90%
probability of >6" of snow across northwest/central South Dakota,
but has also crept up into the 50-70% range for the northern Black
Hills/Rapid City area. It`s in this area where large scale forcing
is a bit uncertain, but upslope enhancement is more likely.
Froude/RH profiles favorable for upslope enhancement, especially
Sunday night. Low level flow also maintains N-NE winds, so Rapid
City should avoid the downslope hole. Thermal profiles support
potential for a bit of rain/freezing rain early Sunday across
south central South Dakota.

Went with Winter Storm Watch for much of the area north and east
of the Black Hills. With the stronger winds on the plains, gust
45+ mph, included blizzard wording in the Watch. Will likely need
some fine tuning on start/end times of the hazards as we get
closer to the event.

Will be chilly after the snow as high pressure drops across the
Dakotas. Extended guidance paints the potential for another snow
event for the end of the forecast period.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 526 AM MDT Fri Mar 22 2024

MVFR CIGS with areas IFR conditions in -SN will occur much of
northeastern Wyoming and western South Dakota through this morning
with improvement to VFR with areas of MVFR CIGS this afternoon.
After 07Z on Saturday AREAS MVFR/LCL IFR conditions in -SN will
redevelop.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from Saturday evening through Monday morning
     for SDZ001-002-078.
     Winter Storm Watch from late Saturday night through Monday
     morning for SDZ012>014-024>026-031-032-072-073.
     Winter Storm Watch from Sunday morning through Monday afternoon
     for SDZ043-044-046-047-049-077.
WY...Winter Storm Watch from late Saturday night through Monday
     morning for WYZ057-060.
&&

$$

DISCUSSION/KEY MESSAGES...7
AVIATION...10


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