658
FXUS63 KUNR 180546
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1046 PM MST Mon Nov 17 2025

.KEY MESSAGES...

- Rain ending tonight.

- Mainly dry this week. A slight chance of rain Tuesday night over
  northwest South Dakota and a slight chance of rain and snow
  Wednesday night over the Black Hills.

- Above average temperatures continue through the week.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 129 PM MST Mon Nov 17 2025

Upper level and water vapor analysis depicts a closed low over
Colorado, southern Wyoming, and the Nebraska panhandle with weak
ridging over Nevada and Idaho, and another closed low coming onshore
into northern California. At the surface, a frontal boundary extends
from central Montana, through northeastern Wyoming and southwestern
South Dakota, into the Nebraska Sandhills. Radar is showing two
distinct bands of rain, one over northwestern South Dakota and a
larger band over southwestern South Dakota. In-between the two bands
are scattered light showers.

For tonight the upper low will move eastward through Nebraska and
into Iowa by morning. Wrap around rain will end by 06Z in most
locations, with a few lingering showers still possible in south
central South Dakota through 12Z. The heaviest precipitation this
evening will continue along the 700 mb theta-e advection which
closely follows the Cheyenne River to Lake Oahe. Temperatures remain
above freezing, thus have kept rain as the dominant precipitation
type. Additionally, areas of fog will likely develop tonight with the
recent moisture. Multiple models are indicating areas of fog
developing tonight and continuing into Tuesday morning across Black
Hills and most of western and south central South Dakota. HREF
probability is 20% to 40% for dense fog along the eastern foothills
and adjacent plains; thus, will continue to monitor trends in case
fog highlights are needed.

A broad upper ridge will develop on Tuesday over the Northern Plains
and will remain over the forecast area through Thursday. At the
surface, a lee trof will develop over northeastern Wyoming Tuesday
afternoon from a surface low over southeastern Montana. This trough
will turn into a weak cool front that will slide into south central
South Dakota late Wednesday. A few rain showers are possible
Tuesday night over northwest South Dakota and a little bit of
precipitation (rain and snow) may develop over the Black Hills
Wednesday night behind the front. Additionally, temperatures may
be a few degrees cooler on Thursday.

For Friday, temperatures look to warm into the 50s as a storm system
tracks south of the area, through the Southern Plains, resulting in
dry conditions for the forecast area. After that, model solutions
diverge significantly. Some solutions bring a system through the
forecast area in the Monday/Tuesday time frame, while other
solutions keep the system over the Southern Plains while hinting at
a possible northern stream system later in the week. Regardless, it
looks like the next chance for precipitation will be next week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1042 PM MST Mon Nov 17 2025

Areas of rain will end from west to east in the overnight hours.
Lingering areas of MVFR/IFR ceilings are expected overnight.
Areas of fog are also expected to develop overnight into early
Tuesday morning over the Black Hills and adjacent western SD
plains. There is also a chance for patchy dense fog, however lower
confidence in that. Have included lower visibilities of 1SM at
KRAP TAF starting at 18/12z.


&&

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

$$

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