458
FXUS63 KUNR 281115
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
515 AM MDT Thu Aug 28 2025

.KEY MESSAGES...

- Isolated to scattered showers possible this afternoon, severe
  weather is not expected.

- More widespread precipitation chances possible over the weekend.

- Temperatures to remain around average through the next week

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 306 AM MDT Thu Aug 28 2025

Current radar imagery shows isolated shower activity
over northwestern SD into southeastern MT. Water vapor imagery shows
monsoonal moisture wrapping around weak upper level ridge and
streaming into the Northern Plains. An upper low sits over the
Pacific Northwest. 500mb vort max will move through the region
today, bringing chances for showers and storms this afternoon and
evening. Marginal instability (SB CAPE of 500-1500 J/kg) will be in
place over southern SD into northeastern WY this afternoon, however
deep layer shear will be weak, precluding any chances for organized
convection and severe weather.

Series of disturbances continues to move through the Northern Plains
Friday into Saturday as the upper low drifts eastward. Chances for
showers and storms will continue into the weekend, with severe
potential remaining very low. PWAT values of 1-1.5" will support
heavy rainfall in the stronger updrafts. LREF grand ensemble paints
70-90+% probs of total precip through the weekend exceeding 0.25"
over much of the CWA. Deterministic output shows some spots over the
western SD plains could pick up 0.75-1.0" QPF by Monday morning.
Upper ridge builds over the western US late in the weekend into
early next week, which will mean a drier pattern for the beginning
of next week. May see a slight warm up early next week as ridge
tries to strengthen, but overall expect average temperatures
(70s to 80s) through the forecast period.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 509 AM MDT Thu Aug 28 2025

Patchy dense fog and associated IFR/LIFR conditions will continue
across south central SD before dissipating after ~15z. Isolated -SHRA
will increase in coverage over northeastern WY into southwestern
SD through this morning. SHRA/TSRA coverage will expand eastward
through this afternoon to cover most of the CWA. Local and brief
MVFR/IFR conditions possible with heavier precip, otherwise VFR
through period.

&&

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

$$

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