088
FXUS63 KUNR 272339
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
539 PM MDT Fri Jun 27 2025

.KEY MESSAGES...

- There is a slight risk (level 2 of 5) for severe thunderstorms
  this afternoon and evening, mainly east of the Black Hills. Main
  hazards will be large hail (quarter size or larger) and damaging
  wind gusts.

- There is a slight risk (level 2 of 5) for severe thunderstorms
  tomorrow afternoon and evening, mainly east of the Black Hills.
  Hazards will be large hail (quarter size or larger) and damaging
  wind gusts.

- Heat shifts east on Saturday, with widespread highs in the 90s

&&

.DISCUSSION...(This Evening Through Friday)
Issued at 140 PM MDT Fri Jun 27 2025

Water vapor imagery depicts the upper level wave over western SD
into northeastern WY. Attendant low level trof sits over
northwestern SD into northeastern WY. Sfc obs depict sharp
dewpoint gradient across the CWA with stations over the western SD
plains reporting dewpoints in the 50s to upper 60s and stations
over the Black Hills, southwestern SD, and northeastern WY
registering dewpoints in the 40s. SBCAPE is 2000+ J/kg across much
of the western SD plains per mesoscale analysis. 18z KUNR RAOB
shows nearly 4000 J/kg SBCAPE with a strong cap in place (-150+
CIN). This is all to say that a very unstable (albeit capped)
airmass sits over most of western SD at this hour. Most recent
CAMs have somewhat limited the coverage of convection this
afternoon. A few storms may develop over the Black Hills and push
eastward. Steep lapse rates and modest deep layer shear should
support a damaging wind and large hail threat. Tornado potential
will be low (though not zero) due to high LCLs and limited low-
level shear. Timing for greatest severe threat this afternoon
still looks to be between 20z and 04z. Another weak disturbance
will cross the region later tonight, which could support another
round of convection, however forecast confidence is very low.

Another hot day on tap for Saturday as low level thermal ridge
noses back into the region. Highs will once again climb into the
90s, especially east of the Black Hills. Weak baroclinic zone will
sink into the northwestern portions of the CWA by the afternoon
hours. Ascent associated with Q-vector convergence associated with
the right entrance of an upper level jet stream may support
convection Saturday evening into the overnight hours, especially
across the southern tier of the forecast area. While CAPE will be
lower (though still in the 500-1500 J/kg range), deep layer shear
will be higher. This could support another round of severe weather
Saturday evening with damaging wind and large hail being the
primary hazards of concern.

A more robust upper level trough will develop over the northern
CONUS Sunday with attendant sfc front sagging south of the CWA.
This will drop our highs slightly (in the 80s instead of the 90s)
for Sunday afternoon. Some showers and storms may develop Sunday
afternoon, especially across southwestern and south central SD,
however severe potential is low at this time.

Ridge builds into the region as the trough moves eastward. This
will facilitate the return of warmer temperatures to the region
through the next week. In addition, northwest flow will set up
over the CWA as the ridge develops. This will support chances for
at least daily chances for isolated convection from Tuesday onward
as weak disturbances move along the upper level flow and
southerly flow continues to advect warm and moist air into the
region.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 536 PM MDT Fri Jun 27 2025

Outflow from convection north of KRAP will arrive within next
15-30 minutes (after ~00z), which will shift winds abruptly out of
the northwest. While convection is expected to stay north of
KRAP, have introduced a prob30 group for thunder through 02z.

Areas of convection will persist across portions of western South
Dakota through the evening and overnight hours. Expect transient
MVFR/IFR conditions and gusty, erratic winds near any
thunderstorms.

Otherwise, VFR conditions are forecast.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...SE