559
FXUS63 KUNR 291713
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1113 AM MDT Sun Jun 29 2025

.KEY MESSAGES...

- Isolated to scattered strong to severe storms will again be
  possible today, mainly across southwestern South Dakota and
  northeastern Wyoming.

- Dry and seasonable conditions expected on Monday.

- Hot with chances for isolated storms Tuesday through at least
  Thursday.

&&

.DISCUSSION...(Today Through Saturday)
Issued at 243 AM MDT Sun Jun 29 2025

Widespread thunderstorms continue over the region at this hour.
Severe potential has waned, but a cluster of storms near the
northern Black Hills/Bearlodge Mountains has supported near-severe
hail over the past hour, whereas a weakening storm between the
Cheyenne and White Rivers has support wind gusts around 50 mph.
Thunderstorms should persist thru much of the night, gradually
shifting southward with a band of deep moist convergence in
association with a midlevel frontal passage. Zooming out, water
vapor imagery shows the upper trof axis remains to our west tonight,
with multiple embedded vort maxima/disturbances stretching from
southern CN into MT.

One shortwave trof digs into the north central CONUS through the
day, becoming increasingly amplified as the trof axis crosses the
region late tonight into tonight. This approaching wave could
support convective initiation over and near the Black Hills, where
PWATs remain at 125-150% of normal. 00z HREF mean SBCAPE values
remain in the 500-1000 J/kg (or slightly higher) range, coupled with
deep-layer shear vector magnitudes of 35 to 40 kt, which could
support some strong to severe updrafts. Relatively straight
hodographs and skinny CAPE profiles suggest marginally severe
splitting supercells may be the primary mode, at least initially,
with some upscale growth potential later in the day.

Strong Q-vector divergence and associated subsidence overspreads the
region on Monday behind the aforementioned trof. Accordingly, a
surface high/low-level ridge shifts over the area as low-level
thermal ridge begins to nose into the region. Taken together, a
warm, sunny day is in store. 00z ensembles show a high likelihood of
temperatures falling within 5 degrees of climo (70s and 80s).

Tuesday and beyond, deep ridging still appears poised to set up from
the southern Plains/Four Corners northwestward through the northern
Rockies, with the northern Plains on its eastern periphery. An
associated low-level thermal ridge extends east into the
central/northern High Plains, with above normal temperatures
becoming increasing likely. Increasing CAPE and deep-layer shear
will also promote a return of at least isolated storm chances, some
of which could end up being strong or severe. The ridge axis shifts
overhead on Thursday and may give way to either zonal or southwest
flow aloft by Friday, but diverging model solutions lead to
decreased confidence late in the period.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1108 AM MDT Sun Jun 29 2025

Isolated to scattered thunderstorms will create localized IFR/MVFR
conditions as well as wind gusts of 40 kt or greater and hail.
Storms will continue through 00Z around GCC and through 03Z around
RAP. Outside of storms, VFR conditions should prevail.

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...Smith