Red Elm, South Dakota Weather Forecast Discussion

813
FXUS63 KUNR 182330
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
530 PM MDT Thu Sep 18 2025
.KEY MESSAGES...
- Precipitation ends Friday morning with some fog overnight
- Drier and warmer for the weekend
- Low confidence forecast next week
&&
.DISCUSSION...(This Evening Through Thursday)
Issued at 203 PM MDT Thu Sep 18 2025
19z surface analysis had low over central SD with upper low
stacked above it per water vapour loop. Weakening showers
continue rotating around it with some weak diurnal showers popping
up over western SD per shallow buoyancy (18z KUNR sounding). Some
cumulus further west with water vapour showing the next wave of
interest over eastern MT.
Tonight/Friday morning, central SD shifts east/northeast
(precipitation in the east wanes) as eastern MT shortwave spins
through the CWA. MT shortwave moisture will be limited, but most
guidance (including CAMs) suggest a band of showers will drop
through the western half of the CWA overnight. Very weak MUCAPE,
but enough for a few lightning strikes. Recent moisture and
converging T/Td spreads later tonight/Friday morning suggest
patchy/areas of fog will develop. Showers/clouds could suppress
extent, but plenty of potential to leave in the forecast.
Temperatures will be near guidance.
Upper/thermal ridge builds into the northern plains later Friday
into the weekend with drier/warmer conditions expected.
Low confidence forecast next week. LREF mean flow suggests an
open wave moves through early in the week with upper ridge
thereafter. However, some ensemble guidance has a significant
upper low moving across the plains with the CWA on the northern
periphery which would create big changes to the NBM forecast. Stay
tuned.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 523 PM MDT Thu Sep 18 2025
Light rain showers will linger across portions of NW SD through
the early evening. While the precip is gradually expected to
dissipate, MVFR/IFR CIGS may linger overnight into Friday. VFR
conditions are otherwise expected across NE WY and western SD
this evening. MVFR/IFR conditions are possible after 06z as low
clouds/fog develop across NE WY and the far western SD plains, but
this should dissipate by ~15z. An area of showers is also
possible from NE WY to central/southern Black Hills into SW SD
between 06z-12z.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...13

NWS UNR Office Area Forecast Discussion