478
FXUS63 KUNR 271812
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1212 PM MDT Sun Sep 27 2026

.KEY MESSAGES...

- Scattered showers and storms at times through Monday.

- Seasonal and dry after Monday.

&&

.DISCUSSION...(This Afternoon Through Saturday)
Issued at 1112 AM MDT Sun Sep 27 2026

SW CONUS upper trough will direct copious amounts of Pac moisture
and embedded impulses over the Rockies and into the region. This
will support a decent chance of showers and storms for much of the
FA, best chances over the SD Plains. Stronger northern stream
trough will then force a stronger cold front into the region Wed
night, supporting a brief cool down. Moisture filled SW flow aloft
with embedded impulses will continue to support rounds of showers
and TS chances through Monday as low level Gulf moisture spreads
west. Lead pos theta-e adv continues to support elevated showers
and storms in the far eastern FA with a few light showers across
scentral SD. LL moist easterly upslope flow continues to support
widespread cloud cover over much of the western SD Plains, except
for far NW SD. The next impulse will arrive later tonight and
support another round of rain chances, mainly after midnight, with
more isolated chances before given lack of appreciable forcing.
Northern CONUS impulse will force a sfc trough into the FA Monday.
This feature will provide the focus for afternoon/evening showers
and storms, esp on the SD Plains where deeper low level moisture
will be in place. Isolated strong to severe cells are possible as
flow increases aloft with the approaching upper level trough, esp
across NW SD. Rain chances will shift east overnight with things
drying out Tues. Expect seasonal temps to continue after today
with highs in the 70s most places through Wed. Deeper upper trough
will advect across southern Canada and support a stronger cold
front into the region by Wed night. This will allow for much drier
and cooler air to shift south across the Northern Plains, with
much cooler weather for Thur. However, this will be short lived as
shortwave ridging is expected for the end of the week, bringing
warmer but continued seasonal weather after.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1212 PM MDT Sun Sep 27 2026

While coverage of fog and attendant visibilities are improving, a
large shield of IFR to LIFR low stratus continues to blanket large
portions of the South Dakota plains, and portions of this will
likely remain in place through tonight. KRAP is expected to see
largely MVFR cigs. VFR conditions will continue through NE WY.

Isolated to scattered showers, and isolated thunderstorms, are
possible this afternoon, tonight, and Monday, with that potential
increasing as we head into tonight. Agreement on timing is poor
among high-res models, but have added PROB30s to KGCC and KRAP
starting tonight. Instability is limited, but seems sufficient
enough to warrant including the thunder potential in the forecast
at this time. As we head toward Monday morning, periods of more
predominant showers may emerge from future model runs at the TAF
terminals, but confidence remains too low at this juncture.

&&

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

&&

$$

DISCUSSION...JC
AVIATION...KSmith