089
FXUS63 KUNR 170453
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1053 PM MDT Wed Sep 16 2026

.KEY MESSAGES...

- Cooler and wetter pattern expected through Monday.

- Return to near average temps by the middle of next week.

&&

.DISCUSSION...(Tonight Through Wednesday)
Issued at 947 PM MDT Wed Sep 16 2026

04Z upper level analysis has high amplitude trof across the West
Coast, with strong closed low over northern California at the
moment. Zonal flow currently resides across the Northern Plains.
Skies are mostly clear across the area, with some thin cirrus
moving in from the central Rockies. At the surface, high pressure
is present across the Dakotas, with a weak frontal boundary just
to the south of the forecast area. Temperatures at 10pm are in the
50s and 60s with light north to northeast winds.

Quiet and mild conditions will continue into the morning hours as
weak ridging holds across the area. Some patchy fog may persist
into the early morning hours across the South Dakota plains.
Temperatures today will mainly be in the 70s to around 80
degrees, with cloud cover increasing through the day as the next
system moves into the area. Strong shortwave in southwest flow
will lift into the Northern Plains late today, bringing rain
showers and isolated thunderstorms to much of the forecast area. A
few stronger storms are possible, but widespread severe weather
is not anticipated at this time. Best chances for precip will be
from the Black Hills area through southern parts of SD. Many
locations in this area could see half an inch to an inch of
precipitation through early Friday morning.

This shortwave shifts east of the area Friday mid morning with dry
and mild conditions expected for the daytime period. As the
western upper trof nudges closer to the area, additional chances
for light rain will occur across northeastern Wyoming by Friday
evening, spreading into far western SD after midnight.

Upper trof/closed low crosses the Northern Rockies on Saturday.
Cool and cloudy conditions are expected with rain chances slowly
increasing from west to east across the forecast area.
Temperatures should only rise into the 60s for most areas, with
northeastern WY and the Black Hills seeing the best chances for
precipitation through Saturday night. A tenth to a quarter inch of
precip will be possible.

Coolest and wettest day occurs on Sunday as the upper low tracks
right across the forecast area. Upper 50s to lower 60s are likely
for most locations, with a quarter to half an inch of additional
precipitation likely. Upper low shifts slowly east Sunday night,
with lingering light precipitation and cool temperatures expected
to stick around on Monday.

Weak ridging finally makes headway back into the region for the
middle of next week, with milder temperatures moving back into the
area.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1037 PM MDT Wed Sep 16 2026

Calm and VFR conditions are expected for northeast WY through the
night. Patchy fog may develop across the central SD plains.
Confidence on its westward extent is low, so it has been left out
of the current forecast for KRAP. Thursday afternoon, a weather
system will move in from the SW and bring mostly rain showers,
with some thunder possible early on. IFR ceilings are expected to
develop as the rain continues through the day. These conditions
will last through the end of the forecast period.

&&

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

$$

DISCUSSION...15
AVIATION...Schweigert