306
FXUS63 KUNR 251117
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
517 AM MDT Fri Jul 25 2025

.KEY MESSAGES...

- Marginal risk (level 1 of 5) for severe thunderstorms this
  afternoon and evening.

- Chance for isolated to scattered storms Saturday, some may be
  strong to severe.

- Hot temperatures across south central South Dakota Saturday and
  Sunday with heat advisories exceeding 100F.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 336 AM MDT Fri Jul 25 2025

Near zonal, west/southwesterly upper level flow continues across
the Northern Plains at this hour. A series of subtle perturbations
along the flow have triggered weak convection across ND into
southeastern MT. Some of this convection may drift into
northwestern SD - hence have kept isolated PoPs in for the rest of
tonight/early this morning. Unsettled flow will continue over the
region today with another weak wave progged to cross the region
by this afternoon. Much like with many of the set ups we`ve had in
the past week or so, there will be a fair amount of buoyancy due
to ample moisture and warm air advection (SB CAPE progged to reach
2000+ J/kg over much of western SD) with enough deep layer shear
to support organized convection (20-30kt). However, there`s some
question as to how much forcing the incoming shortwave may
provide. CAMs depict at least isolated storm development by this
afternoon, primarily across northwestern SD where forcing will be
better. Some storms may fire over the Black Hills where terrain
induced convergence will provide forcing, however drier air
pushing up into southwestern SD/northeastern WY from the south may
make it into the Black Hills by the afternoon hours which will
limit storm chances. Main hazards of concern with any stronger
storms that develop this afternoon and evening will be large hail
and damaging winds.

Somewhat drier weather is generally anticipated through this
weekend as upper level ridge/high builds into the southern US.
However, can`t rule out at least isolated chances for storms as
weak shortwaves ride the southwest flow. Continued WAA thanks to
southwesterly flow will support temperatures in the mid to upper
90s by Saturday. With dewpoints reaching into the mid to upper 60s
across south central SD, heat indices will approach 100F (HREF
shows 70+% probs of apparent temps exceeding 100F over Mellette
and Tripp Counties for Saturday). Therefore have hoisted a Heat
Advisory for Mellette and Tripp Counties for Saturday afternoon.
These areas could potentially need heat advisory for Sunday but
will leave that for later shifts.

Upper ridge continues to strengthen and retrograde westward
through early next week with continued southerly flow bringing
moist air into the region. Temperatures will moderate somewhat by
Tuesday/Wednesday as a cold front sweeps through the region.
However, daily chances for precip will continue as ridge riding
shortwaves advect across the region. However, timing and strength
of these waves (as well as any potential severe threat) remain
uncertain at this time.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 515 AM MDT Fri Jul 25 2025

VFR conditions expected to prevail through the valid TAF period.
The exception will be with any isolated TSRA that may develop
across northwestern SD and the Black Hills this afternoon with
strong, erratic winds, hail, and LCL MVFR conditions.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM to 8 PM CDT Saturday for SDZ046-049.
WY...None.
&&

$$

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