702
FXUS63 KUNR 310439
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1039 PM MDT Fri Oct 30 2026

.KEY MESSAGES...

- Areas of dense fog return tonight into Saturday morning.

- Mild and mostly dry this weekend

- Rain and potentially strong northwest wind gusts Monday into
  Monday night; some light snow possible over the higher Black
  Hills.

&&

.UPDATE...
Issued at 1001 PM MDT Fri Oct 30 2026

Latest nighttime microphysics RGB loop showed extensive stratus
over the CWA, but nothing too low at this point. T/Td spreads are
starting to converge with southeasterly upslope flow on the
western SD plains. Areas of fog, potentially dense, will develop
overnight and persist into Saturday morning before quickly burning
off to a nice Fall day for most folks. Where stratus hangs on
(like today), temperatures may be 5-10F than current forecast
suggests.

Then Sunday night and Monday, upper trough/low eject from the
southern Rockies in the northern Plains spreading well-defined
synoptic lift over the CWA. Gulf moisture will be entrained into
the system, especially east of the Black Hills. Looks like a good
setup for high PoPs with some folks seeing 1"+ of QPF per several
ensemble guidance depictions (northern Black Hills and toward
south-central SD. ECMWF EFI gives 70-90th percentile QPF with
shift of tails (SoT) of 1 to 2. System looks to have strong gusty
northwest winds behind it with 60-80th percentile wind gusts with
a bit of SoT. Bufkit momentum transfer forecasts also robust. Wind
headlines seem likely as areal coverage and strength become more
apparent this weekend.

&&

.DISCUSSION...(This Evening Through Friday)
Issued at 123 PM MDT Fri Oct 30 2026

A slow-moving deep upper trough is sitting just offshore the Pac NW.
Southwesterly flow is stretching across most of the western CONUS
into the northern Plains. WV imagery shows a strong shortwave
crossing the Great Basin into WY. Surface obs show S/SE winds
continuing with temps in the 40s to lower 50s at this time. Temps
are struggling to warm across NW SD where low clouds/fog has
lingered. Webcams show visibility has improved quite a bit but some
fog is lingering especially across higher ridges and buttes. Low
clouds will persist tonight with fog/drizzle expected to redevelop
and expand across large portions of the western SD plains up to the
foothills of the Black Hills...and even stretch back into portions
of the NE WY plains. The fog will likely be dense again over some
areas through Saturday morning. Dense Fog Advisories may be needed
again. Weak ridging ahead of the incoming shortwave will bring some
warm air advection in tonight into Saturday. Highs in the 60s to
near 70 are expected, but if low clouds/fog end up lingering longer
than expected across the western SD plains, this could keep temps
cooler than forecast. Generally dry weather is expected Saturday,
though could see isolated showers across south central SD late Sat
as the shortwave crosses the region. The Pacific trough/low will
finally make its way across the western CONUS through Sunday.
Surface low pressure will develop across eastern WY through the CO
Front Range. Southerly return flow will increase ahead of the low
across the Neb/SD plains. Highs on Sunday will be in the 60s, but
then cooler weather is expected Monday as colder air is ushered in
on the backside of the low as it crosses the northern/central
Plains. Strong forcing with this system will bring extensive
rainfall to the region, but models at this time show most of that
rain falling across East River SD. However, rain is still expected
across the CWA...though lower amounts. The exception may be the
northern Black Hills where upslope enhancement could bring higher
totals. There still remains much uncertainty as to how much QPF the
area might see. Gusty NW winds are also expected Monday into Monday
night, but again, there is disagreement as to how strong these winds
might be. Another variable to consider is how much snow the higher
Black Hills might see. This system is quite warm, but light
accumulations are possible across the highest terrain, depending on
how much precip remains as colder air arrives. It`s another aspect
of the storm we`ll be watching through the weekend.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1038 PM MDT Fri Oct 30 2026

Widespread MVFR/IFR with transient LIFR conditions in fog and low
stratus will persist through the overnight hours across NE WY and
western SD. Some improvement expected across far western SD and
NE WY after 15-17z as fog dissipates. MVFR ceilings will linger
into Saturday afternoon, especially across NW SD into central SD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

UPDATE...Helgeson
DISCUSSION...13
AVIATION...SE