Custer, South Dakota Weather Forecast Discussion

845
FXUS63 KUNR 130822
AFDUNR
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
222 AM MDT Sat Sep 13 2025
.KEY MESSAGES...
- Unsettled weather to continue through the remainder of the
  weekend
- Potential for locally heavy rainfall through Sunday
- Warm start to the work week on Monday, then cooling with more
  precipitation chances
&&
.DISCUSSION...(Today Through Friday)
Issued at 220 AM MDT Sat Sep 13 2025
Latest satellite imagery shows 500hpa trough/low across the
inter-mountain west, with ridge axis nosing northeast from central
TX into the Great Lakes area. Shortwaves ejecting into the
northern plains are bringing widespread showers and thunderstorms
to the region. At the surface, an area of low pressure is located
in the vcnty of KVTN with an inverted sfc trough nosing northward
along the Missouri river into central ND. There is another
trailing sfc trough southwest through the NE panhandle and into
northeast Colorado.
Showers and thunderstorms associated with lead ejecting wave early
this morning should lift into ND by early afternoon, leaving
mostly dry conditions behind. Ensembles are showing mean layer
CAPE values aoa 1300 J/kg with 30-35kt shear around the Black
Hills, and with sufficient moisture around, will need to keep some
low pops going there for the afternoon period. As things lift
northward, there should be a general decreasing trend in
cloudiness from west to east as well.
Thoughts then turn toward tonight and Sunday. Main 500hpa trough
ejects onto the plains with strong southerly fetch of moisture
ahead of it. By 18z Sunday PWAT values from the Black Hills and
eastward climb into the 175-225% of normal range. Ensembles are
showing 24 rainfall probabilities of 1.5 from 20-45% for much of
the area east of the Black Hills by mid-afternoon Sunday. Again,
locally heavy rainfall is expected with some of the stronger
storms and if south to north training cells, might have to keep an
eye of flash flood guidance.
700hpa theta-e downglide moves in behind exiting system, helping
to dry things out for the area beginning Sunday night and
continuing into Monday. Temps at 850hpa warm through the day with
the WY counties most likely being the warmest on Monday. This warm
up appears to be short-lived as the next 500hpa trough moves into
the region bringing an increase in cloudiness(ie...cooler temps)
and more unsettled weather for the remainder of the week.
&&
.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1050 PM MDT Fri Sep 12 2025
A few brief drops to MVFR conditions can not be ruled out
tomorrow morning along a stationary boundary, though VFR
conditions are expected to prevail across the airspace.
North/northwest winds will remain largely sub 10 kts over the next
24 hours or so. Isolated showers and storms will be possible
around 00Z, though confidence was not high enough to include in
TAF.
AEH
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Herdliska

NWS UNR Office Area Forecast Discussion