907
FXUS63 KUNR 300747
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
147 AM MDT Sat Aug 30 2025

.KEY MESSAGES...

- Unsettled/coolish through Sunday afternoon, then more
  seasonable early next week
- Cold front Tuesday night brings cooler temperatures Wednesday,
  but then back to seasonable for the rest of the period

&&

.DISCUSSION...(Today Through Friday)
Issued at 145 AM MDT Sat Aug 30 2025

07z surface analysis had several diffuse troughs from eastern MT
into western KS. They are reflections of diffuse upper trough from
southern AB to the southern Plains. Embedded shortwaves
responsible for isolated/scattered shra/TS across the northern
Plains early this morning. CWA saw a lull late Friday evening,
but latest KUDX radar loop depicts slowly increasing coverage
northeast of the Black Hills. Main concern this forecast is
diffuse upper trough.

Through Sunday afternoon, diffuse shortwave-laden upper trough
slowly slides southeast as it weakens. Surface troughs follow
similar path. SPC HREF portrays ~500J/kg mean MUCAPE during peak
insolation this afternoon/evening and ~250J/kg Sunday afternoon.
0-6km bulk shear weak. CAMs show diurnally-driven popcorn TSRA
over the western half of the CWA this afternoon/evening with
better coverage convection over the eastern half where beneficial
rainfall may occur given PWATs at 125-175% of normal. Activity
Sunday afternoon will be near the Black Hills terrain and over the
eastern reaches of the CWA, but coverage looks noticeably lower
given drier air starting to filter into the region. Upslope
component to boundary layer flow will support stratus/patchy fog
at times, but especially at night given diurnal temperatures
fluctuations. Temperatures will be near guidance, except perhaps a
few below east of the Black Hills per clouds cover/highest PoPs.

Sunday night through Tuesday afternoon, upper ridge over the west
expands into the Rockies putting CWA under sustained northwest
flow aloft. Drier air should preclude most PoPs, but chances
aren`t zero. Cold front slices through the northern Plains Tuesday
night bringing a chance of shra/TS later Tuesday into Wednesday
along with cooler MaxT Wednesday. Rest of the week sees a return
to seasonable weather with limited PoPs per probabilistic
guidance.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 903 PM MDT Fri Aug 29 2025

Shower coverage will be more sparse through the night before
increasing in coverage again during the day Saturday. Instability
will increase during peak heating, so continued a PROB30 group at
each TAF site after 18Z/30. There is a signal for lower stratus
and possibly some patchy fog overnight into Saturday morning.
Generally expecting MVFR ceilings and visibilities; however, an
IFR ceiling can`t be ruled out by Saturday morning.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Cooley