071
FXUS63 KUNR 241139
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
539 AM MDT Fri Jul 24 2026

.KEY MESSAGES...

-A blocking pattern will support a ridge of high pressure over
 the CONUS this weekend into next week, supporting very hot
 temperatures and elevated fire weather concerns

-Thunderstorms will be possible at times this weekend into next
 week as monsoon impulses advect around the ridge and into the
 region

&&

.UPDATE...
Issued at 955 PM MDT Thu Jul 23 2026

Shower/storm activity has largely diminished across the CWA with
only a few spotty light radar returns over western SD. Water vapor
imagery shows dry air moving into the region with the monsoonal
moisture now to our south. Conditions downright muggy tonight with
dewpoints in the 60s to near 70 across much of western SD into
northeastern WY. With the ample low level moisture, light winds, and
clearing skies overnight we could see some localized fog develop in
the river valleys over the western SD plains, but potential coverage
not enough to warrant mention in the grids.

Much hotter for the weekend as upper ridge strengthens over the
Northern Plains. Still looking like much of the western SD plains
will hit the triple digits for Saturday through Monday with advsy
level heat indices expected. In addition to the heat, monsoonal
moisture will still advect into the region, supporting the
development of high-based storms Saturday afternoon as weak wave
moves across the area.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 1232 PM MDT Thu Jul 23 2026

Upper level ridge over the Rockies will shift east and expand
over the central CONUS. This will result in very hot temperatures
this weekend into next week. Departing batch of monsoon moisture
will support scattered showers and storms into the evening as
diurnal heating allows for expansion in coverage this afternoon.
Locally heavy rainfall will be possible given high PWATs and slow
movement. Upper ridge will begin to shift east Friday although a
ridge topping impulse will shift a trough across the southern
Canada and the Dakotas, with the tail end of the trough stalling
in the FA later tomorrow. Much warmer temps tomorrow with highs in
the 90s most places, with a few low 100s possible in areas on the
Plains. Aforementioned upper trough may support a few isolated
showers or storms across NW SD in the afternoon, carried a low pop
for this. Separate weak impulse may also support a shower or
storm across northeast WY in the evening and so have also added
low pops there as well. Upper ridge will shift east Sat with very
hot temps expected. Highs will reach 100 or higher for most
locations on the Plains, supporting adv level heat index readings.
Low level moisture will deplete some with mixing, but sustained
southerly flow will prevent the BL from drying out too much most
places. This will help keep heat index readings higher, esp over
central SD. Heat looks to persist at least through Tues, possibly
longer depending on how passing ridge periphery impulses affect
the ridge. Expect that there will be TS chances at times in this
period as monsoon moisture advects around the NW side of the
ridge. This includes Sat when another monsoon wave will advect
around the ridge in SW flow and into the FA later Sat, supporting
high based TS chances. Gusty winds will be possible with any
thunderstorms in this period given high based nature and near
inverted-V profiles. Ridge will retrograde back west some by mid
next week, supporting slightly cooler but still hot temps, with
expected TS chances as the lee trough interacts will passing
impulses.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 528 AM MDT Fri Jul 24 2026

Patchy morning fog has popped up around the area. Looking ahead,
the fog should fade out over the next 1 to 3 hours. Then, VFR
conditions are expected throughout the forecast period.

&&

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

$$

UPDATE...Wong
DISCUSSION...JC
AVIATION...GS