Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 061939
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
139 PM MDT Sat Apr 6 2024

.KEY MESSAGES...
131 PM MDT Sat Apr 6 2024

- A large spring storm will bring widespread rain and some heavy,
wet snow to the region into Monday. The snow will be confined mostly
to northeastern Wyoming and the Black Hills tonight through Sunday
night. The highest combined impact of snow and wind likely will be
over Campbell County.

- Gusty southeast winds will continue over central SD through this
evening.

- The storm exits on Tuesday, which will be followed by a warming
trend.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 131 PM MDT Sat Apr 6 2024

Upper-level analysis shows low over northeastern CO, with a large
moisture plume emanating northwards across WY/MT, and a secondary
plume that has developed over NE/western SD. Heavy showers are
moving into western SD from Nebraska; currently thunderstorms
remain to our south. The surface low is over southwestern NE,
resulting in strong ESE winds across western and especially
central SD, and breezy northerly winds over northeastern WY. Under
cloudy skies, temperatures are in the 40s and 50s.

Precipitation will wrap into northeastern WY and western SD as the
low gradually tracks northeastward through the weekend. This
evening, showers and isolated thunderstorms will continue across
parts of western SD; however with MUCAPE <500 J/kg, not expecting
any severe storms. As the low deepens over NE tonight, increasing
PVA and PWATs will support heavier precipitation across the CWA.
Cooler air will wrap into the region tonight, with rain changing
to snow, especially over the higher elevations of northeastern WY
and the Black Hills. Accumulating snowfall will continue over
those areas through Sunday, gradually tapering off through Monday.
While mainly rain is expected on the plains of western SD, there
is the potential for some snow in the lower elevations of the
foothills, including Rapid City, Sunday morning. Amounts will
depend heavily on temperature and if/when it begins to accumulate.
The 12Z HREF shows a 60% chance of Rapid City receiving >1 inch
of snow by noon Sunday, with a 30% chance of >3 inches. However,
the NBM has lower chances: its 95th percentile is 1-2 inches.
Latest models have shown the upper low retrograding a bit Monday,
keeping precipitation around longer. A longer duration of snowfall
over northeastern WY and the BH have resulted in a slightly
higher snow total forecast. The 12Z HREF has likely (65-100%)
chances of >12 inches across Campbell County and the northern
Black Hills, with some places having >50% chance of >18 inches of
snow. Current forecast includes 2 feet of snow in the highest
elevations of the Black Hills and the southwestern corner of
Campbell County. Precipitation will gradually end late Monday.

Strong southeasterly winds will continue through tonight across
central SD, so will leave the Wind Advisory intact. Areas to the
north will be near advisory criteria. Northwesterly winds will
continue to increase across northeastern WY as the pressure
gradient tightens behind the surface low. As rain changes to snow,
blowing snow will become possible. Winds will gradually diminish
Sunday as the low shifts eastward.

The upper low will push into Canada on Tuesday, and warmer air will
start moving back into our region. Before drier weather settles in,
however, a shortwave will bring the chance for rain showers on
Wednesday. Upper ridging will then build over the western CONUS for
the end of the week. Temperatures will warm into the 50s by
Thursday, with 60s and lower 70s expected Friday and Saturday.


&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1120 AM MDT Sat Apr 6 2024

A strong storm will bring deteriorating conditions today and
tonight as well as gusty winds. Rain will develop across the area
by 18z, rapidly expanding this afternoon. Isolated thunderstorms
will also be possible. The rain will change to snow across
northeastern WY and the Black Hills by evening. MVFR conditions
will expand this afternoon, become widespread IFR tonight. LIFR
conditions are likely over northeastern WY/Black Hills where
heavy snow falls.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning from 6 PM this evening to 6 AM MDT Monday
     for SDZ024-028.
     Winter Weather Advisory from 6 PM this evening to 6 AM MDT
     Monday for SDZ041.
     Wind Advisory until midnight CDT tonight for SDZ046-047-049.
WY...Winter Storm Warning from 6 PM this evening to 6 AM MDT Monday
     for WYZ054>058.
&&

$$

DISCUSSION/KEY MESSAGES...Pojorlie
AVIATION...10


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