831
FXUS63 KUNR 242222
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
422 PM MDT Sun Aug 24 2025

.KEY MESSAGES...

- Mild temperatures will continue through early part of week
  before a warming trend starts.

- Region will remain mainly dry through mid-week as Canadian high
  pressure remains in place.

- More unsettled weather expected for the latter half of the week

&&

.DISCUSSION...(This Evening Through Sunday)
Issued at 131 PM MDT Sun Aug 24 2025

Latest satellite imagery shows broad 500hpa trough located across
eastern half of the CONUS, with deep 500hpa 4-corner high pressure
located across the southwest CONUS. CWA is located in quick
moving NW flow aloft. At the surface, high pressure is located
across the eastern Dakotas with light easterly/east-northeast
surface flow and surface dewpoints in the upper 30s to mid 40s.

For tonight, the question is if there will be any overnight
shra/tsra that develops along the SD/NE border. There is a noted
700hpa theta-e ridge that slides quickly through in the nw flow
with minor amounts of forcing. Some of the CAMS develop some
popcorn returns across northwest/north central Nebraska in
response to this forcing. Moisture is awful meager, however
ensembles are showing pcpn probabilities of 0.01 or greater at
15-20% across our south eastern counties aft 06z, so will need to
account for these.

For Monday, coolish temps will remain in place as surface high
pressure is still located across the eastern Dakotas. Of note is
the coolish temps at 700hpa (+4C) and 500hpa (-12C). This should
be enough to help develop potential light showers/tsra over the
Black Hills during peak heating, and the ensembles are also
painting 15-20 probabilities during the afternoon across the Black
Hills for this. With no shear and mean PWATS generally under
0.75, really not expecting a whole lot to come of it, but will
need to account for it.

Beginning Tuesday and carrying through the remainder of the week,
500hpa heights rise along with increasing 850hpa temps. A
developing western CONUS trough will work to begin to break down
the strengthening 500hpa ridge...turning upper flow from NW into a
more zonal pattern. This should allow more desert SW monsoonal
moisture to work northward into the region. Coupled with
disturbances moving through in the zonal flow pattern, and
developing low pressure and eastward oriented boundary through the
state, things will become more unsettled heading into the second
half of the week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 421 PM MDT Sun Aug 24 2025

VFR conditions are expected through the TAF period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Wong