209
FXUS63 KUNR 290510
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1110 PM MDT Thu Aug 28 2025

.KEY MESSAGES...

- Unsettled conditions to start off the holiday weekend.

- Cool for the weekend, then warming to seasonable temps for next
  week.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 110 PM MDT Thu Aug 28 2025

Latest satellite imagery shows a couple of 500hpa disturbances
crashing through the Rocky Mtn 500hpa ridge. Large 500hpa
low/trough located across eastern CONUS with developing west coast
trough also seen. At the surface, broad high pressure is located
across the central Dakotas with a couple of surface lows (SW SD
and NC Wyoming) associated with aforementioned 500hpa shortwaves.
These are currently assisting with the development of light
shra/tsra across our Wyoming counties into the western Black Hills
and southwestern SD.

As the series of 500hpa disturbances continue to flatten the ridge
to the west, pcpn chances will increase overnight through Saturday
across the region. Not really too concerned about the
probabilities of severe weather as shear is rather blah at 25
kts or less across the area and CAPE values are generally under
750 J/kg through the period of concern. What is eye catching is
the PWAT values through 06z Sunday. Values are on the order of
150% to 200% of normal. Ensembles are showing probabilities of
total rainfall greater than 1 on the order of 40 to 50 % along
and north of I-90, then across SC SD through 12z Sunday, and even
25-35% probabilities of 1.50 total rainfall for the same area. So
while severe weather wont be a threat, locally heavy rain sure
could be with some of the stronger storms.

Beginning Sunday and through the remainder of the fcst, western
CONUS ridge rebuilds to our west, leaving CWA in dry NW flow
regime with no well defined disturbances sliding through. While it
wouldnt be totally out of the question for isolated
showers/storms to develop across the Black Hills in this flow
pattern, there really isnt much to hang your hat on. About the
best chance of seeing anything in the extended might occur Tuesday
night into Wednesday when the next series of 500hpa/700hpa troughs
drop quickly through the area.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday morning)
Issued At 1110 PM MDT Thu Aug 28 2025

Unsettled weather will impact flying conditions through this TAF
issuance. Scattered showers and storms are expected intermittently,
with the best chances for thunderstorm activity Friday afternoon and
evening. VFR conditions are expected to be the predominant flight
rules; however, where heavier downpours occur, visibility may
briefly drop as low as 2 miles. There are some hints at lower
ceilings toward the very end of the TAF period with upslope flow and
steadily increasing moisture. This would most likely impact KRAP.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Cooley