123
FXUS63 KUNR 171715
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1115 AM MDT Mon Aug 17 2026

.KEY MESSAGES...

- Active pattern persists through mid-week with daily chances of
  storms, some of which may be strong to severe.

- Trending warmer to end the week into next weekend.

&&

.UPDATE...
Issued at 1005 PM MDT Sun Aug 16 2026

Storms have mostly cleared the CWA, heading into Nebraska and
central SD. The rest of the night should be quiet...except could see
a stray shower across far south central SD overnight. A weak cold
front/dry line will push into the CWA on Monday. Best instability
will be ahead of the front mainly from the I-90 corridor southward.
There is enough shear for some strong/severe storms with large
hail/damaging winds. Highs Monday will be in the 80s. An upper wave
is then expected to cross the CWA Monday night, bringing late
evening and overnight showers/isolated storms.

&&

.DISCUSSION...(This Afternoon Through Saturday)
Issued at 1129 AM MDT Sun Aug 16 2026

Upper level analysis shows zonal flow across the Northern Plains
this morning with subtle embedded shortwaves upstream. Upper ridge
is building over the SW US with weak height rises over the area
and generally limited upper level ascent. Diffuse surface high
pressure is centered over central SD/ND with southeasterly surface
flow across the area.

Isolated to scattered thunderstorms are expected this afternoon
across the area despite the weak upper level forcing. Forecast
MLCAPE 500-1500 J/kg will be in place, although effective bulk
shear will be marginal (25-35 knots). Best potential for
thunderstorm coverage is expected across the Black Hills given
orographic lift where transient supercellular structures/severe
weather is possible with the strongest convection through the
evening hours.

Active northwest flow is forecast Monday with additional showers and
thunderstorms. The best chance for severe weather will be along the
theta-e axis focused across southern SD into south-central SD.

Daily chances of showers and thunderstorms persists through Wednesday.
A robust upper level ridge will overspread the region by the end
of the week into the weekend with much warmer temperatures expected.
Current guidance has us on the northeastern periphery of the
ridge axis with fairly active northwest flow across the region,
resulting in continued chances of storms.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1110 AM MDT Mon Aug 17 2026

Isolated showers continue to push east through the western SD
plains. Additional showers and storms are expected to develop
across the area after 20-21z this afternoon. Gusty, erratic winds,
small hail, and lightning are the main threats. While timing is
still uncertain with respect to impacts at KRAP and KGCC, have
introduced PROB30 groups at each airport; better chances for MVFR
conditions in any stronger cells at KRAP from 21z-04z and 00-03z
at KGCC. Otherwise, outside of any convection, VFR conditions are
expected.

&&

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

$$

UPDATE...13
DISCUSSION...SE
AVIATION...SE