935
FXUS63 KUNR 080431
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1031 PM MDT Mon Jul 7 2025

.KEY MESSAGES...

- Isolated to scattered severe storms possible this afternoon
  through early evening.

- Hotter and mostly dry conditions arrive tomorrow, with hot
  temperatures continuing into Wednesday.

- Chances for storms increase Wednesday afternoon through early
  Friday.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 104 PM MDT Mon Jul 7 2025

Water vapor imagery this afternoon shows a midlevel disturbance
shifting from east to west over the north central CONUS, with
enhanced moisture extending from southern MB/ON southwestward thru
the Missouri River Valley. This wave is supporting a corridor of
elevated convective showers and storms extending westward toward the
Badlands. South of this corridor, north to northeast winds indicate
a subtle outflow boundary that has pushed south of most of our area
outside of far south central SD. Meanwhile, a trailing front can be
identified with northwest winds around the Cheyenne River
southwestward to along the I-90 corridor in SD and WY.

Cumulus fields at the current hour from south central SD west-
southwestward through the Pine Ridge area northwestward into
northeastern WY, with a separate area along/behind the front near
the Cheyenne River, likely demarcate areas of appreciable surface-
based buoyancy. Latest SPC mesoanalysis field suggests a capped 500-
1000 J/kg of MLCAPE paired with effective bulk shear magnitudes of
30-40 kt in these areas. With continued heating, MLCAPE may increase
as high as 1500-2000 J/kg in spots, particularly across south
central SD ahead of the front. Here, the environment will become
increasingly favorable for supercells conditionally capable of all
hazards if a discrete mode can become established before the front
arrives. Farther west, from southwestern SD through the Black Hills
into northeastern WY, slightly weaker deep-layer shear and drier
boundary layers (corresponding to higher LCLs) will favor a more
transient supercellular mode with low-end severe hail (quarter sized
to around ping pong ball sized) and strong to severe winds the
primary threats. If any storms manage to develop along the northern
Black Hills, a locally favorable environment for all hazards with
enhanced MLCAPE, lowered LCLs, and terrain-enhanced shear may favor
more rapid storm intensification. Given recent trends, this appears
unlikely. The main front will likely cross the area from northwest
to southeast by around 03z, bringing a relatively early end to
convection and severe potential compared to recent days.

As the trof axis continues to shift eastward, rising heights
overspread the region in its wake tonight into tomorrow. Midlevel
height ridging and associated low-level thermal ridge building into
the area should promote a return of hot and mostly dry conditions
tomorrow, though a storm or two cannot be ruled out near the Black
Hills/over northeastern WY. HREF mean SBCAPE of 1000-2000 J/kg with
deep-layer bulk shear magnitudes of 20-30 kt may support some strong
updrafts if initiation occurs. An increasing number of convectively
induced potential vorticity anomalies riding atop the ridge over the
central/northern Rockies into the High Plains may support more
widespread thunderstorm activity by Wednesday despite continued
large-scale ridging and warming low-level temperatures. Increased
buoyancy but similar/decreased shear compared to Tuesday will be
somewhat of a wash in terms of severe potential, but some
strong/severe storms may occur.

A pair of potent shortwaves approach the region Thursday into
Friday. The first is projected to arrive from the west beginning
Thursday morning. The timing of this wave has slowed slightly since
yesterday, which would bring it through the area closer to peak
heating vs. beforehand, particularly across eastern portions of the
area. However, environmental parameter space doesn`t look especially
suitable for severe weather given marginal deep-layer shear (20-25
kt; LREF probabilities of 30+ kt of 0-6 km bulk shear magnitudes 30%
or lower across most of the area). Still plenty of wrinkles to be
ironed out, but timing/environmental concerns preclude much
confidence in potential for severe hazards. Broader, more amplified
trof crosses the region Thursday night through Friday. As cooler air
spills into the area behind the initial wave, CAPE will be limited
ahead of this second wave as deep-layer shear increases; as such,
expecting showery convection with potential for embedded thunder vs.
any strong/severe concerns overnight Thursday into Friday.
Tightening pressure gradient, pressure rises, and cold air advection
behind the associated front will likely bring breezy northwest winds
through the day Friday.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1029 PM MDT Mon Jul 7 2025

Mainly VFR conditions are expected through the TAF period. The
exception would be MVFR conditions in any storms that develop late
Tuesday afternoon.

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...Pojorlie