440
FXUS63 KUNR 151110
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
510 AM MDT Wed Oct 15 2025

.KEY MESSAGES...

- Dense fog/patchy drizzle this morning, but patchy/areas of fog
  will linger through tonight
- Unsettled through Thursday
- Isolated strong/severe thunderstorms tonight parts of
  northeastern WY/southwestern SD
- Drying out this weekend with seasonal weather

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 225 AM MDT Wed Oct 15 2025

08z surface analysis had high over the Great Lakes and trough
from eastern MT into central CO. Low level moist east/southeast
flow between the two feeding fog/dense fog/patchy drizzle across
much of the CWA early this morning per surface
observations/highway cameras. Water vapour loop showed upper low
spinning over southern NV with shortwave-laden southwest flow over
the northern Plains. Wave over WY creating shra/TS over
northeastern WY per regional radar loop/GLM data. Forecast concern
continues to be upper low.

Today/tonight, upper low ejects into the central Rockies. Surface
low spins up along surface trough in northeastern CO. Low level
moist east/southeast flow will continue with dense fog/drizzle
early this morning and improving visibilities late
morning/afternoon, but fog will still linger into tonight for some
folks. Current Dense Fog Headlines look good. As surface low
spins up, a narrow band of 0.5-1KJ/kg MUCAPE (SPC HREF) is
forecast to poke into the CWA from the south late this
afternoon/tonight. Given expected stratus/fog surface-based
convection developing in the CWA might be tough, but elevated
buoyancy/effective shear may be sufficient for isolated
strong/marginally severe thunderstorms (hail/wind) this evening
over southwest portions of the CWA. Otherwise, band of shra/TS
will invade the CWA tonight affecting the western half the most
with a 40-60% chance of 0.50" QPF per HREF where the band sets up.
Forecast PWATs 150-200% of normal, so locally heavy rain possible
if any training develops. Have lowered temperatures for MaxT
today courtesy of stratus/fog.

Thursday, upper low moves into southern MB with dry slot over the
eastern half of the area. Additional showers likely on the back
side over the west with any daytime heating conducive to popcorn
showers especially over northeastern WY. Temperatures will be near
guidance.

Friday into the weekend, northwest flow aloft is replaced with
upper ridge with drier weather and a warming trend. Progressive
flow early next week creates low confidence forecast as a series
of upper troughs move across the northern Plains. Typical Fall
pattern.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning)
Issued At 507 AM MDT Wed Oct 15 2025

Areas of fog, some drizzle, and low clouds will persist through
the forecast period with IFR/LIFR conditions, although some
improvement may occur this afternoon and early evening. A storm
system will spread rain and a few thunderstorms (hail and gusty
winds possible) into the area late this afternoon, persisting
into tonight as the precipitation moves south to north.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 9 AM MDT /10 AM CDT/ this morning for
     SDZ001-002-012>014-024>032-041>044-046-047-049-072>078.
WY...Dense Fog Advisory until 9 AM MDT this morning for WYZ054-056-
     057-060.
&&

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Helgeson