996
FXUS63 KUNR 182339
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
439 PM MST Tue Nov 18 2025

.KEY MESSAGES...

- Patchy/Areas of fog tonight.

- A few showers across northwest South Dakota tonight.

- Above average temperatures continue through the week.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 149 PM MST Tue Nov 18 2025

Upper level and water vapor analysis shows a shortwave ridge
building across the forecast area as the exiting upper low tracks
toward the Great Lakes, a strong closed low begins to move onshore
into southern California, and a small robust low spins in
southeastern British Columbia. Additionally, a weak shortwave is
seen moving northward out of north central Wyoming into southern
Montana. At the surface, a stationary front extends southward from a
low in southern Saskatchewan through eastern Montana and
northeastern Wyoming, into the Nebraska Panhandle. Regional radar
shows light precipitation in the Mountains over north central
Wyoming and southern Montana while visible satellite shows fog and
stratus over a large portion of the western South Dakota plains.

For tonight, the energy over Montana will push slowly into
southeastern Montana, skirting the Wyoming/Montana border and far
northwestern South Dakota, before exiting around daybreak
Wednesday. At the same time, the surface stationary front will
slide slowly eastward into far western South Dakota as a warm
front. This will result in some areas of fog continuing into this
evening and overnight along the eastern foothills and across
northwestern South Dakota.

By Wednesday morning, areas of fog look to be concentrated mainly
over northwestern South Dakota, behind a weak cold front. The
front will push southeastward through the area, exiting south
central South Dakota by late afternoon. The lingering morning fog
and the cooler air behind the front will have an impact on
temperatures, with warmer readings across southwestern and south
central South Dakota.

Fairly tranquil conditions are expected for Thursday and Friday with
an upper level split flow pattern in place. The upper low over
British Columbia will slide eastward through Canada in the
northern stream while the low over southern California shears
apart crossing the southern Rockies. This will allow a weak ridge
to form across the forecast area, resulting in mostly clear skies
and warming temperatures.

By the weekend, the forecast trends back to quiet northwest flow.
A few impulses move through, but the Pacific moisture dries out
crossing the Rockies. This will lead to a continuation of above
average temperatures and dry conditions.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 436 PM MST Tue Nov 18 2025

Areas of fog and low ceilings are expected this evening with MVFR/IFR/LIFR
conditions across portions of western South Dakota. Some
improvement to transient MVFR/VFR conditions is expected after
19/06-08z tonight. Low vis fog may persist overnight, mainly over
northwestern SD, however cannot rule out them reaching back into
KRAP in the 10-16Z timeframe.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Dye