Opal, South Dakota Weather Forecast Discussion

919
FXUS63 KUNR 200657
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1257 AM MDT Sat Sep 20 2025
.KEY MESSAGES...
-Dry and warmer this weekend
-Rain chances return early next week
-Uncertainty remains in forecast details next week given
 tendencies for a blocking pattern with a transient closed upper
 low
&&
.DISCUSSION...(Today Through Friday)
Issued at 1256 AM MDT Sat Sep 20 2025
Stubborn upper trough over the Northern Plains/Upper Midwest will
continue to slowly shift east today, allowing for warmer and dry
weather this weekend as a ridge of high pressure slides east.
Light winds, clear skies, and lingering low level moisture will
support fog on the SD Plains this morning. Much warmer this
weekend with highs in the 70s and 80s, warmest Sunday. A weak
moisture starved impulse will shift over the region today and
support some thicker cirrus, likely enough to dim the sun at
times. Deep upper trough in the northeast Pac will split this
weekend, sending an impulse into the northern Rockies. This system
will move into the region early next week, supporting a cold
front into the FA Monday, with breezy northwest winds expected.
Forecast models close this low off while offering a blocking ridge
over the western CONUS. The upper low then looks to phase with
the Great Lakes trough, supporting a quasi-omega block. This will
support poor model performance as forecast models do not typically
handle cut off lows very well. Hence, low confidence in forecast
details beyond Monday. The latest runs suggest bringing precip
through Monday with showers shifting south of the FA by Tues.
Expect this will likely change as the pattern evolves, so stay
tuned. The Rockies ridge will eventually shift east later in the
week, potentially bringing warmer temps into the region when it
does. However, there is some major model dependencies wrt to flow
details across southern Canada and the northeast Pac, which would
highly affect forecast details locally. Hence, forecast temps do
not deviate too much from climo norms in this period attm.
&&
.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1036 PM MDT Fri Sep 19 2025
After 06z patchy fog may develop on the SD plains with local MVFR
to IFR conditions, which my reach the KRAP terminal in the early
morning hours. Fog is expected to lift late morning, with VFR
conditions then expected the remainder of the period.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...JC
AVIATION...Dye

NWS UNR Office Area Forecast Discussion