204
FXUS63 KUNR 261714
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1114 AM MDT Sat Sep 26 2026

.KEY MESSAGES...

-Another lobe of tropical moisture expected Sunday into Monday,
 supporting more chances for rain

-Cool Sunday, especially on the SD Plains

-Seasonal and dry after Monday

&&

.DISCUSSION...(This Afternoon Through Friday)
Issued at 1059 AM MDT Sat Sep 26 2026

Upper trough will remain in place through early next week over
the western CONUS, supporting mainly WSW flow aloft. Pattern
change expected toward next weekend as a strong NE Pac upper
trough dives into the Pac NW and supports a couple stronger upper
troughs and associated sfc low`s across southern Canada and the
northern CONUS, flattening the flow aloft. Sfc trough has pushed
through most of the FA. A period of breezy winds can be expected
into the afternoon, esp in the lee of the Black Hills. Not much if
any cool air with this front, just a drier airmass. Upper trough
will drop into the SW CONUS Sunday and direct tropical moisture NE
across the Rockies. Meanwhile low level SE return flow will
develop, pushing LL moisture back west into the region. This will
support much cooler conds on the SD Plains for Sunday, esp along
the east slopes of the BH where moist upslope flow will be in
place. Expect mostly cloudy skies there with light showers or
drizzle possible. Isolated light rain showers will also be
possible across the remainder of the SD Plains as pos theta-e adv
will be ongoing through the day. Main lobe of deep moisture will
arrive in the evening via a lead impulse, supporting a good chance
of showers and isolated TS. Another window of higher chances of
showers and storms can be expected Monday afternoon as the sfc
trough moves through the area, with a few stronger storms possible
on the SD Plains. Things dry out after Monday with seasonal temps
expected into the upper 60s to low 70s the rest of the week, lows
in the 40s/50s. Models are still indicating a stronger cold front
next weekend, which could bring some frost as the upper trough
over the NE Pac shifts east and forces cold air south out of
Canada. However, the degree of CAA with this system still varies
substantially among the various forecast models and ensembles,
with temperature spreads really large.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1112 AM MDT Sat Sep 26 2026

Low clouds will continue to move out of northwestern and south-
central South Dakota throughout the early afternoon leading to
VFR conditions overall. Patchy fog and low clouds will redevelop
Saturday night into Sunday morning resulting in IFR/LIFR
conditions across portions of south-central and southwestern South
Dakota. Rain showers and isolated thunderstorms will move into the
region, starting around 27/04-06z, and MVFR ceilings may impact
KRAP starting around 27/12z and last through the remained of the
TAF period.

&&

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

$$

DISCUSSION...JC
AVIATION...Schultz