Grashul, South Dakota Weather Forecast Discussion

334
FXUS63 KUNR 091704
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1104 AM MDT Tue Sep 9 2025
.KEY MESSAGES...
- Above normal temperatures through Thursday.
- Precipitation chances increase Friday into Saturday with
  temperatures moderating.
&&
.DISCUSSION...(Today Through Monday)
Issued at 255 AM MDT Tue Sep 9 2025
09Z upper level analysis has weak shortwave trof just east of the
forecast area, with western ridge building across the Northern
Rockies and Northern High Plains. Skies are mostly clear across
the forecast area, with a small line of light showers across
northern Crook County in Wyoming at the moment. At the surface,
weak high pressure is in place, with frontal boundary and low
pressure across North Dakota. Temperatures across the forecast
area at 3 AM are in the 50s and 60s, with light west to northwest
winds.
Upper ridge will continue to build into the Northern Plains today
into tonight, with mainly dry conditions continuing. This
afternoon, a few isolated showers and storms will develop across
northeast Wyoming and the Black Hills, and persist into the early
evening hours across southwest portions of SD. Temperatures today
will be warm, in the 80s for most locations on the plains.
Upper ridge axis slides out into the Northern Plains on Wednesday,
with southwest upper flow moving into western portions of the
forecast area. Western trof and associated surface low strengthen,
and shift into the Central Rockies. Tight surface pressure
gradient develops across the area by Wednesday afternoon,
producing breezy southeast winds. Winds of 15 to 25 mph will be
likely, especially across northwestern SD. Once again, some
isolated showers and storms will be possible across much of the
area. Temperatures remain above average.
Upper ridge shifts well east on Thursday, with the forecast area
under strong southwest flow. Surface low lifts into eastern
Montana, with strong southerly boundary layer flow continuing
across the area. Isolated storm chances continue, along with above
average temperatures.
Western trof finally shifts into the Northern Rockies on Friday,
with significant changes in sensible weather for the area. Cold
front and widespread moisture work into western portions of the
forecast area, with temperatures cooling to more seasonable
levels. Upper trof persists over the area into Saturday, with
precip chances remaining high for most of the area. Operational
GFS remains the outlier with this system, keeping better precip
chances north and west of the area. Interesting that a
significant number of GFS ensemble members agree with the Euro and
Canadian on bring better precip across western SD. Will see how
this plays out over the next several model runs.
Unsettled weather lingers into Sunday, before weak ridging ahead
of the next western trof brings drier conditions to the area
early next week.
&&
.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1102 AM MDT Tue Sep 9 2025
Isolated showers and storms are expected through 06Z across parts
of northeast Wyoming and southwestern South Dakota. VFR conditions
will continue through the period.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...15
AVIATION...Smith

NWS UNR Office Area Forecast Discussion