290
FXUS63 KUNR 282329
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
529 PM MDT Sat Jun 28 2025

.KEY MESSAGES...

- Isolated to scattered storms (some severe) this afternoon,
  mainly along and south of I-90. Primary hazards will be damaging
  wind gusts and large hail.

- Thunderstorms continue through tonight into Sunday, with locally
  heavy rainfall possible

- Drier on Monday. Chances for isolated thunderstorms return
  Tuesday and Wednesday.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 211 PM MDT Sat Jun 28 2025

Visible satellite imagery shows CU field developing across
northeastern WY and along a sfc boundary over the Black Hills. Sfc
obs show dewpoints in the 50s to 60s across much of western SD
into northeastern WY with drier air over southwestern SD and
nosing into the Black Hills. Corridor of 2000+ J/kg CAPE has
developed across much of the western SD plains and northeastern WY
with mostly clear skies allowing plenty of sfc heating. 18z UNR
RAOB does show a modest capping inversion from 850-775 mb which
has limited convection thus far. Isolated storms may develop over
the Black Hills and higher terrain in WY where terrain driven
convergence and upslope flow should be sufficient to overcome the
cap. Any updrafts that form this afternoon will encounter 40kt
bulk shear which will be sufficient for rotating updrafts. With
the relatively fat CAPE profile, dry boundary layer, and modest
low to mid level lapse rates of ~7-8 C/km, main concerns with any
stronger convection will be large hail and damaging winds. Later
tonight, converging outflow boundaries from this afternoons storms
may contribute to a predominately linear mode with a damaging
wind threat becoming the main concern. Additionally, PWAT values
approaching 150-175% of normal will support heavy rainfall with
storms tonight.

Upper level trough deepens and moves to the east through Sunday
with baroclinic zone sagging southward through the area. This
frontal boundary could support more convection Sunday afternoon.
In terms of severe potential, widespread severe weather isn`t
expected with afternoon CAPE values approaching 1000-1500 J/kg,
however 30-40kt 0- 6 km shear could support a few stronger
updrafts.

Ridge builds into the region Sunday night into Monday with large
scale subsidence and drier air supporting a warm and dry day
Monday. The ridge will also facilitate the return of warmer
temperatures to the region through the next week. Northwest flow
will set up over the CWA as the ridge remains to our west. This
will support chances for at least daily chances for isolated
convection from Tuesday through the mid week as weak disturbances
move along the upper level flow and low level southerly flow
continues to advect warm and moist air into the region.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 525 PM MDT Sat Jun 28 2025

Scattered severe thunderstorms will continue through 06z mainly
east of the KRAP terminal. Expect large hail and vrb25g35kt with
the stronger storms. Aft 06z MVFR conditions are possible late in
the period as a backdoor front crosses the region and more
widespread showers and storms. West of the Black Hills region VFR
conds are expected through the valid terminal period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...Hintz