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000
FXUS63 KUNR 242301
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
501 PM MDT Wed Apr 24 2024

.KEY MESSAGES...

- Thunderstorms with heavy rain expected Thursday afternoon and
  evening, with some hail and gusty winds.

- Widespread rain will develop Friday morning and continue through
  Sunday, bringing abundant moisture to the area.

- Warmer and drier weather expected early next week.

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 240 PM MDT Wed Apr 24 2024

Low amplitude upper ridge axis is slowly crossing the central to
northern Rockies, ahead of a split trough extending along the
Pacific Coast. A weak upper low is crossing southern to central
California and will push northeastward toward Colorado tonight and
Thursday. Surface high pressure has pushed into the Great Lakes
region, with strong return flow now over the area. Temperatures are
currently in the 60s to mid 70s. One last quiet night is expected
tonight before the unsettled, wet pattern develops. Theta E
advection tonight and tomorrow will bring dewpoints into the upper
40s/low 50s across western South Dakota by Thursday afternoon. With
temps reaching into the 70s across most areas, forecast soundings
suggest SBCAPE values to 1500 J/kg. The best 0-3 SRH seems to be
mismatched with the strongest instability. The strongest shear will
be over central SD, where gusty SE winds are expected...and weakest
across northeast WY. Severe weather will be limited by just weak
shear across the Black Hills/far western SD. However, there is
enough instability for storms to produce hail and gusty winds...and
a few perhaps producing large hail...as they push eastward off the
Black Hills into increasingly better shear. PWATs are in the 150%
range in the early afternoon, then increasing to 175-200% by late
afternoon/evening. Models suggest the stronger storms may produce
over an inch of QPF through the evening. The storm system will
become better organized and strengthen Thursday night/Fri morning as
it pushes into western Nebraska. Wrap-around precip will fill in
across the CWA, especially over western SD, where a band of heavier
precip is expected. Northerly winds will develop, which will bring
upslope enhancement to the northern Black Hills area. Right now it
looks like half an inch to an inch of QPF will fall on Friday across
portions of western SD, with locally higher amounts over the
northern Black Hills. A second system will dig across the Four
Corners region late Friday and lift into the central Plains Saturday
into Sunday. As precip wanes from the first system, redevelopment is
expected with this second system Saturday into Sunday. This system
will be farther east, which could bring the highest QPF to south
central SD into East River on Sunday...but some uncertainty remains
with this track. It does look like light rain will continue to fall
over the rest of the area through much of the weekend. Breezy
northeast winds may bring slight upslope enhancement across the
northern to eastern foothills Saturday into Sunday morning. By
Sunday afternoon, much of the forecast area could see QPF amounts of
1 to 2 inches...maybe even 3 inches across some spots. Drier weather
will finally move in late Sunday into Monday...with warming
temperatures for the first half of the week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 449 PM MDT Wed Apr 24 2024

Isolated showers, and possibly a thunderstorm, may occur near the
SD/NEB border early this evening. Isolated showers are then
possible over northeastern Wyoming, the Black Hills area and
southwestern South Dakota tonight through Thursday morning.
Showers and thunderstorms will increase in coverage and intensity
after 20Z on Thursday afternoon. VFR conditions will continue
overnight with areas of MVFR CIGS developing over south central
South Dakota after 11Z on Thursday morning and continuing through
the Day. Mainly VFR conditions are expected over the rest of the
area with LCL MVFR conditions possible with the stronger showers
and thunderstorms on Thursday afternoon.

&&

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

$$

DISCUSSION/KEY MESSAGES...13
AVIATION...10