Belle Fourche, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

746
FXUS63 KUNR 142055
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
255 PM MDT Thu Aug 14 2025

.KEY MESSAGES...

- Hot through this evening, with heat indices around 100 degrees
  across south-central SD.

- Near-critical fire weather conditions over northeastern WY and
  portions of far southwestern SD through this afternoon.

- Daily chances for isolated thunderstorms, some of which could
  be strong to severe, expected through the period.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 255 PM MDT Thu Aug 14 2025

Water vapor imagery this afternoon shows a midlevel disturbance over
the eastern Dakotas shifting into the Upper Midwest. Lingering
subsidence behind this wave is maintaining mostly clear skies
areawide, though some shallow cumulus is beginning to become evident
via satellite imagery. The most notable development is ongoing over
the eastern Black Hills/foothills, where more congested cumulus is
present. Latest surface analysis shows a weakening surface trof over
our eastern zones, with a trailing cold front steadily progressing
southward through the region. The 18z RAOB from Rapid City showed a
fairly deep, well-mixed boundary layer extending to around 3 km AGL
topped with a modest warm nose. However, a slightly more humid
boundary layer behind the approaching boundary combined with the
associated frontal lift and terrain-driven convergence may suffice
for convective initiation sometime in the next couple of hours.
Should initiation occur, MLCAPE of 500-1000 J/kg and effective bulk
shear magnitudes of 35-40 kt may support organized, isolated general
to strong convection. More widespread convection is ongoing over
higher terrain of WY through the Four Corners region where a broad
area of enhanced midlevel to upper-level moisture is present per
water vapor imagery.

Farther east, HREF mean SBCAPE/0-6 km bulk shear magnitudes climb to
2-3 kJ/kg and 35-40 kt across south central SD this afternoon.
However, solutions are split: With higher CAPE, the cap holds in
forecast soundings; with sufficient mixing to break the cap,
boundary layer moisture decreases, owing to lower CAPE and less
favorable thermodynamic profiles on the whole. At least modest (~-25
J/kg or more) CIN values persist through peak heating per HREF
mean/median. Given no cumulus development so far this afternoon, any
convective initiation may be difficult to attain until 850 mb
frontogenesis arrives around or after 00z with the secondary
boundary behind the weakening surface trof. The SPC maintained a
level 1 of 5 (marginal) risk for severe weather in its latest
update, which is reasonable given the environment`s potential but
relatively low probability of convective initiation. Outside of
storm potential, heat indices continue to hover around 100 degrees.
Advisory criteria heat indices are a bit more localized than
anticipated owing to mixing; nonetheless, maintained the advisory
with this package. Drier heat is present over far southwestern SD
and prefrontal areas of northeastern WY, where observations have
occasionally reached Red Flag criteria this afternoon. Durations and
extents of critical fire weather conditions are expected to be
limited given marginal winds, so will not introduce any headlines at
this time. Beyond today, LREF combined probabilities of relative
humidities < 20% and winds > 10 mph are limited to less than 30%
throughout the period, so although very dry afternoons will persist
over portions of northeastern WY and far southwestern SD, critical
fire weather conditions are not expected.

Late tomorrow through the next several days, zonal flow aloft and
weak midlevel ridging will give way to increasingly southwesterly
flow. Early tomorrow, thunderstorm development will likely be
limited by neutral to increasing heights and a stingy cap. Should
initiation occur, a broad corridor of 60%+ probabilities of SBCAPE
over 1500 J/kg and 0-6 km bulk shear vector magnitudes over 35 kt
could easily support organized strong to severe thunderstorms. More
widespread convection will become increasingly probable later in the
afternoon/evening as a weak wave approaches along the eastern
periphery of the trof nosing into the region. Similar daily chances
for storms are likely through most of the period. Relatively weak
shear will further limit potential for strong/severe storms after
tomorrow; however, cannot rule out one or two such storms on any
given day.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1141 AM MDT Thu Aug 14 2025

Isolated/scattered thunderstorms may develop this evening and
tonight with local MVFR conditions, but confidence is low for the
terminals so no mention there yet. Otherwise, VFR conditions are
expected through the TAF period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 8 PM CDT this evening for SDZ046-049.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...Dye