959
FXUS63 KUNR 291056
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
456 AM MDT Fri Aug 29 2025

.KEY MESSAGES...

- Unsettled conditions to start off the holiday weekend.

- Cool for the weekend, then warming to seasonable temps for next
  week.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 306 AM MDT Fri Aug 29 2025

Water vapor imagery depicts weak upper low over northeastern
WY/southeastern MT. Scattered showers are ongoing across
northwestern and southwestern SD, circulating around a weak sfc
low. Could see a few lightning strikes in some of the stronger
cells but generally expecting rain showers through the rest of the
night. Scattered showers will continue through the day today as
the sfc low drifts to the east. Marginal instability develops this
afternoon as SB CAPE rises to 750-1000 J/kg this afternoon.
However not too concerned about severe weather as weak deep layer
shear will be unsupportive of organized convection.

Scattered showers and storms will continue through Saturday as a
series of disturbances moves through the Northern Plains. PWAT
values of 1-1.5" (150 to 200% of normal) will support heavy
rainfall in the stronger updrafts. LREF grand ensemble output
paints 70-90+% probs of greater than 0.25" QPF over much of
western SD by 12z Sunday morning. There are chances for total
precip to exceed 1", primarily over the I-90 corridor into south
central SD (30-40% probs). Some spot could see up to 1.5" or more
where storms train.

Conditions dry out by Sunday as the upper level ridge builds back
into the western US, leaving the Northern Plains under dry,
northwest flow. Can`t completely rule out some isolated and
diurnally driven showers/storms over the Black Hills through
Wednesday as the ridge sits over the western US.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 452 AM MDT Fri Aug 29 2025

Scattered showers and thunderstorms will continue across much of
the forecast area through today. Outside of storms, conditions
will be VFR but LCL MVFR/IFR conditions may be encountered in and
around any precipitation cores. Low stratus with associated
MVFR/IFR conditions may develop tonight, mainly across the western
SD plains.

&&

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

$$

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