006
FXUS63 KUNR 172022
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
222 PM MDT Tue Jun 17 2025

.KEY MESSAGES...

- Isolated to scattered thunderstorms expected today, some of
  which will be strong to severe.

- Warming temperatures and dry conditions are anticipated later
  this week, with highs likely in the triple digits in some
  locations Friday and Saturday.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 222 PM MDT Tue Jun 17 2025

Water vapor imagery this afternoon reveals a notable shortwave trof
moving thru southeastern MT/northwestern WY, which is supporting
areas of convection at this hour. The most notable activity is over
the Black Hills, where enhanced convergence and, likely,
shear/instability are contributing to locally stronger updrafts. The
background environment per the 18z UNR RAOB is not especially
inspiring, with ~200 J/kg of MLCAPE, ~-200 J/kg of MLCIN, and
effective bulk shear magnitudes under 30 kt. However, 12z HREF
suggests a localized bullseye of increased MLCAPE/SRH over the Black
Hills, which is consistent with the observed rotating updrafts and
probable severe hazards with ongoing storms. Environment away from
the Black Hills as sampled by the aforementioned RAOB combined with
CAM solutions suggest that convection may struggle to maintain
intensity as it moves off of terrain. As such, severe potential
could be rather short-lived with this initial activity. However,
another round of strong/severe storms cannot be ruled out as
convection closer to the parent wave matures over northeastern WY
this evening.

Midlevel trof shifts east of the area tomorrow as ridging begins to
build over the Rockies in its wake. Another shortwave trof quickly
shifts eastward atop the ridge late tomorrow into tomorrow night.
Associated modest lee cyclogenesis will facilitate the development
of a weak low-level jet over the High Plains. The associated vapor
transport and convergence (largely focused over southwestern/south
central SD) may be able to support a few elevated showers, but
chances are very low at this time. Thursday into Friday, ridging
generally builds over the Plains/Midwest as a robust trof is carved
out over the West Coast. This trof shifts eastward somewhat Friday,
bringing deep southwest flow to the region. Accordingly, low-level
thermal ridging builds Thursday, Friday, and Saturday. LREF
probabilities of 850 mb temperatures 25-30 C reach ~100% across
northeastern WY by midday Thursday, expanding over most of the area
by Thursday evening. Altogether, the expectation is for well above
normal temperatures late this week through early in the weekend
(potentially record-breaking Friday and Saturday). Confidence
decreases somewhat from Sunday onward, as progression of western
trof will have significant impacts on our sensible weather.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1118 AM MDT Tue Jun 17 2025

A disturbance will bring scattered/numerous shra/TS to the region
this afternoon/evening, most numerous this afternoon over/near the
Black Hills. Local MVFR conditions, gusty winds, and hail will
occur with the stronger cells. Outside of storms, VFR conditions
will prevail. Patchy fog will be possible later tonight into
Wednesday morning, particularly well east of the Black Hills.

&&

.FIRE WEATHER...
Issued At 222 PM MDT Tue Jun 17 2025

After a mild and unsettled day today, dry and warm conditions
will overspread the region tomorrow through the end of the week.
Highs will climb into the 90s over much of the region by Thursday,
with triple digit highs anticipated in some areas Friday and
Saturday. Along with the heat, low relative humidity values and
breezy west to southwest winds will contribute to elevated fire
weather conditions.

&&

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...Helgeson
FIRE WEATHER...Sherburn