832
FXUS63 KUNR 312309
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
509 PM MDT Sun Aug 31 2025

.KEY MESSAGES...

- Mainly dry and warm Monday and Tuesday.

- A cold front will move through Tuesday night, bringing a chance
  of showers and thunderstorms and cooler temperatures for
  Wednesday.

- Another cold front will move through Thursday, with gusty
  northwest winds over the western South Dakota Plains and cooler
  temperatures for Friday.

&&

.DISCUSSION...(This Evening Through Sunday)
Issued at 209 PM MDT Sun Aug 31 2025

Upper level analysis shows a ridge over the Rockies, a low over
eastern Nebraska and another low over northern Canada, resulting
in northerly flow over the western High Plains. At the surface, a
low is centered over eastern Kansas, with a trof extending
northward into the central Dakotas and an area of high pressure
over Wyoming. Radar imagery is still showing showers over central
and northwestern South Dakota.

The showers will gradually end this evening, leaving behind mostly
cloudy skies across the eastern portions of the forecast area.
Areas of fog and low stratus will likely develop again tonight
across the plains east of the Black Hills, as low-level moisture
pools near the surface.

Low clouds/fog will slowly dissipate Monday morning, leaving
behind sunny skies, mild temperatures, and light winds. The upper
ridge will continue to build on Monday and Tuesday, advecting
warmer air into the Northern Plains. Steep lapse rates and daytime
heating could cause an isolated shower/storm over the Black Hills
each day; however, confidence is low, so have opted to leave it
out of the forecast for now.

A cold front will drop southward through the area Tuesday night,
from the Canadian low pressure area that drops southward into
Ontario. This will result in a chance (20- 50%) of showers/storms.
Temperatures will be much cooler on Wednesday, with ensembles
indicating a 10C degree difference from highs on Tuesday.

The upper low over Ontario will strengthen as the ridge over the
Rockies tries to hold, before retrograding westward. This will
bring a tightening pressure gradient and another cold front
through the area on Thursday. Overall, moisture appears to be
limited with this front, but the gradient will likely produce
windy conditions over the western South Dakota plains. Will
continue to monitor, but later shifts may have to consider wind
highlights for Thursday and Thursday night. Temperatures will
again cool with this second front, most likely slightly cooler
than readings on Wednesday.

After that, the upper ridge over the Rockies will again build,
with the axis moving closer to the western High Plains. This will
result in warmer temperatures and mainly dry conditions.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 507 PM MDT Sun Aug 31 2025

Look for patchy fog with resultant MVFR/IFR cigs and vsbys to
develop across the plains of western SD aft 01/08Z. The patchy fog
is expected to lift aft 01/14Z. Otherwise VFR conds are expected
across the region through the valid forecast period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Hintz