Union Center, South Dakota Weather Forecast Discussion

423
FXUS63 KUNR 220536
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1136 PM MDT Sun Sep 21 2025
.KEY MESSAGES...
- A cold front will bring scattered showers, breezy northwest
  winds, and cooler temperatures to the area Monday
- Dry conditions return Tuesday afternoon, with a gradual warming
  trend through late week.
&&
.DISCUSSION...(This Evening Through Sunday)
Issued at 133 PM MDT Sun Sep 21 2025
Upper level analysis has a ridge centered over the Rockies,
flanked by a positively titled trough over the Northern Plains and
another trough just beginning to move onshore across the Pacific
Northwest. At the surface, a low is positioned over southeastern
South Dakota, with an associated boundary stretching westward
through southwestern South Dakota and northward into eastern
Montana. Additionally, a cold front extends from a surface low in
Saskatchewan southward through central and western Montana into
Idaho. The primary forecast challenge early this week will be the
timing and progression of this cold front, as well as the
evolution of the Pacific Northwest trough.
For tonight, ensemble guidance suggests the frontal boundary will
remain draped across the forecast area overnight, while the western
cold front advances rapidly eastward, nearing the western portions
of the CWA by morning.
Monday/Monday night the cold front will sweep through the region,
bringing scattered showers, isolated thunderstorms, cooler
temperatures, and gusty northwest winds. Model consensus continues
to favor a more western track, with the upper trough closing off
later than previously indicated. This delayed evolution will
reduce precipitation chances and QPF, with the highest
probabilities of rain south of Interstate 90.
Scattered showers and isolated thunderstorms are expected behind the
front, particularly where 700 mb theta-e advection is the
strongest across northeastern Wyoming and southwestern South
Dakota. High resolution CAMs depict showers developing over
northeastern Wyoming and the Black Hills Monday morning, spreading
into southwestern South Dakota by afternoon. By midday, the front
should be oriented north-south just east of the Black Hills,
which will bring gusty northwest winds to the South Dakota Plains
and Weston County, WY for the afternoon and evening hours. While
breezy conditions are anticipated, HREF ensemble guidance keeps
wind gusts below advisory thresholds, with less than a 10% chance
of reaching criteria.
By early evening, some CAMs suggest thunderstorm development over
south-central South Dakota, transitioning to more widespread showers
by late evening.
By Tuesday, the cold front will have exited the region, with
lingering showers tapering off during the morning as the upper
trough closes off over southwestern Wyoming. The resulting closed
low will track southeastward through Colorado into southern
Kansas by Tuesday night. This pattern shift will allow the upper
ridge to rebuild over the Rockies and western High Plains,
ushering in a period of dry conditions and gradual warming through
the remainder of the week
&&
.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1131 PM MDT Sun Sep 21 2025
A cold front will push through the region early in the period.
Expect winds to remain south/southwesterly ahead of the front
before becoming northwesterly around or after daybreak. Northwest
winds will increase behind this front with gusts around 25-30+ kts
possible later today. Some fog will develop across the SD plains
this morning, but this should remain east of RAP. Isolated
showers or storms are also possible late today near RAP, but
confidence is too low to warrant a TAF mention.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...Smith
AVIATION...Melo

NWS UNR Office Area Forecast Discussion