Grashul, South Dakota Weather Forecast Discussion

470
FXUS63 KUNR 121910
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
110 PM MDT Fri Sep 12 2025
.KEY MESSAGES...
-Unsettled this weekend with a good chance of showers and
 thunderstorms
-Locally heavy rain possible this weekend from the Black Hills
 region into northwest SD
-Warmer Monday, then cooler and unsettled
&&
.DISCUSSION...(This Evening Through Friday)
Issued at 109 PM MDT Fri Sep 12 2025
Mean western CONUS trough continues to support semi-unsettled
weather across much of the Northern Plains and Rockies. This
system will continue to slowly shift northeast this weekend,
supporting increasingly unsettled weather in the Northern Plains.
Stronger lead impulse ejecting toward the region this afternoon
with TS coverage expected to ramp up later today across the SW FA.
Thunderstorm clusters are expected to grow upscale into to a line
of storms as the system lifts NE. There will be potential for for
a few stronger cells capable of producing strong winds and hail.
Bulk shear is marginal and so is ML CAPE (aoa 1000-1500 J/KG), but
certainly sufficient. Locally heavy rain will be possible with
heavier cells, esp across NW SD later tonight given best expected
moisture convergence. Lingering showers/storms will shift NE out
of the region Sat morning. Dry most places Sat afternoon, except
for around the BH where a unstable conditions will be place for
more afternoon showers and storms. Main wave will lift into the
region Sat night with a strong push of deep moisture. Model
consensus supports the best chances for rain across western SD
where the deformation zone will setup and stall through Sunday.
Rounds of showers an isolated storms looks to support a good
chance of rain there with rainfall amounts over an inch possible
from the BH into NW SD Sat night into Sunday afternoon. Things
will dry out Sunday night with warmer and dry conds expected for
Monday. Another upper trough moves into the region later next
week, supporting additional rain chances as well as a cooler
temps. However, confidence in the track, strength, and resultant
precip chances remain very low attm given progged semi-blocked
flow, which typically leads to high forecast model uncertainty.
&&
.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1156 AM MDT Fri Sep 12 2025
Isold to scattered showers and thunderstorms are expected to
later this afternoon and evening across the forecast area, with
local MVFR cigs/vsbys possible with some of the stronger storms.
otherwise VFR conditions are generally expected. Saturday morning,
low cigs may creep into far northeastern WY and northwestern SD
for a couple hours, but not expected to hinder TAF sites.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...JC
AVIATION...Dye

NWS UNR Office Area Forecast Discussion