457
FXUS63 KUNR 151908
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
108 PM MDT Sat Aug 15 2026

.KEY MESSAGES...

- Active pattern persists through the weekend with daily chances
  of showers and thunderstorms, a few of which may be strong to
  severe today through Monday.

- Trending warmer to end next week.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 106 PM MDT Sat Aug 15 2026

Water vapor imagery shows shortwave trough pushing through
eastern and central Wyoming this afternoon. Northwesterly low
level flow persists behind a surface cold front that stretches
from eastern ND through eastern SD into central NE. Isolated
convection initiated this morning across NE WY with additional
storms expected through the afternoon and evening across NE WY and
the far southwestern portion of the forecast area. MLCAPE values
~250-750 J/kg will be in place this afternoon and evening,
although effective shear will be limited (~30-35 knots or less). A
few storms may be strong to severe (Marginal risk across portions
of NE WY and SW SD), although overall instability and shear
parameter space will will preclude more organized severe
convection.

Upper level ridge flattens Sunday as upper level flow turns zonal
then northwesterly into early next week. Ample instability will
be in place Sunday with effective shear around 35 knots,
supporting threat of transient strong to severe storms. However,
upper level ascent will be weak, limiting extent of the severe
threat Sunday afternoon and evening. Best chance for convection
Sunday afternoon will be across the Black Hills (central and
southern) given orographic lift and across NW SD where better
upper level ascent will be present.

Generally westerly to northwesterly flow will persist through
mid- week with near-daily chances of thunderstorms. Severe threat
Monday is still uncertain and contingent upon timing of the upper
wave and surface front. Sufficient shear is in place Monday
(effective bulk shear 35-50+ knots) for more organized severe
convection should the other ingredients fall into place.

Strong upper ridge is forecast to build over the southwestern US
late next week, spreading into the Rockies and Northern Plains.
Expect temperatures to warm back into the upper 80s to 90s to end
the week into next weekend.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1110 AM MDT Sat Aug 15 2026

Isolated to scattered showers and thunderstorms will be possible
today/this evening. Thunderstorm development will begin around
15/18z and last through 16/06z, mainly over northeast Wyoming, the
Black Hills, and southwestern South Dakota. Transient MVFR/IFR
conditions are possible around any heavier precipitation cores.
Conditions will improve starting around 16/08z, with mainly VFR
conditions expected through the remainder of the TAF period.

&&

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

$$

DISCUSSION...SE
AVIATION...Schultz