Heppner, South Dakota Weather Forecast Discussion

978
FXUS63 KUNR 202326
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
526 PM MDT Sat Sep 20 2025
.KEY MESSAGES...
- Fog develops over the western South Dakota Plains late
  tonight/early Sunday morning.
- Monday afternoon through Tuesday morning, rain showers with
  isolated thunderstorms.
- Dry the remainder of the week.
&&
.DISCUSSION...(This Evening Through Saturday)
Issued at 232 PM MDT Sat Sep 20 2025
Upper level analysis has the forecast area in northwest flow as a
negatively tilted trough remains over the Northern Plains/Upper
Midwest and ridge over the Rockies. At the surface, high pressure
is in place over the Dakotas with a surface low over the Red River
Valley and another surface low over southeastern Wyoming.
For tonight, the surface low over southeastern Wyoming will shift
into south-central South Dakota. Low-level moisture will increase
with light winds allowing for some fog to develop over the western
South Dakota Plains.
The fog will burn off during the morning, with mainly clear skies
for the afternoon. Overall, temperatures will remain warm with
readings about 10F above average.
An upper trough will quickly push through the northern Rockies and
into the region Monday. Models close off the low over Wyoming on
Monday and drop it southward into Colorado Tuesday. Ahead of the
supporting low, a cold front moves through the forecast area on
Monday, resulting in breezy northwest winds and more seasonable
temperatures. Chances for showers and isolated thunderstorms will
accompany the frontal passage on Monday, with some precipitation
wrapping around the low Monday night and Tuesday. The highest
probability of precipitation will be across southern and western
areas, closer to the low with limited precipitation chances across
northwestern South Dakota.
Expect precipitation chances to end from north to south on Tuesday,
as the main upper low drops into the southern plains. Temperatures
will remain cool, but will be close to seasonal averages.
For the rest of the week, expect temperatures to gradually warm with
dry conditions, as high pressure gradually builds across the area.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 524 PM MDT Sat Sep 20 2025
VFR conditions are expected through much of the period. Fog is
expected to develop again overnight on the SD Plains and may
impact RAP early in the morning. Dense fog could be possible in
some areas, especially closer towards central SD.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...Smith
AVIATION...Dye

NWS UNR Office Area Forecast Discussion