543
FXUS63 KUNR 190410
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1010 PM MDT Sat Jul 18 2026

.KEY MESSAGES...

- Hot through the weekend with elevated to near critical fire
  weather conditions.

- A marginal risk (1 out of 5) of severe storms Sunday
  afternoon/evening.

- Slightly cooler conditions finally look to return middle of next
  week.

&&

.UPDATE...
Issued at 945 PM MDT Sat Jul 18 2026

No big changes were made in the forecast. Still expecting the
upper level flow to shift to a more westerly flow, which opens the
door for thunderstorms in the area.

The lingering leftover rain showers that are tracking through
northwest SD this evening will continue to track east while
diminishing overnight. After that, eyes will be on the passing
front that could get the next round of storms going tomorrow. Hi-
res models and the EURO ENS initiate more thunderstorms tomorrow
(Sunday) afternoon, although there is some evidence of storm
initiation over the Black Hills by midday. Once storms initiate,
they`ll track east-to-southeast through the evening.

Some of those storms could be strong to severe. Machine learning
ensemble models put a lean towards strong winds as the main
concern for severe weather in the South Dakota Plains. Both these
machine learning severe weather models and the SPC put a Marginal
(level 1 of 5) risk of severe weather over the South Dakota plains
tomorrow.

Beyond that, the next round for passing storms will be on Tuesday
night into Wednesday.

Temperatures will take a bit of dip midweek as well with highs a
little closer to normal, in the 80s to near 90 Tuesday, Wednesday
and Thursday. The hotter 90s to low 100s return for the weekend.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 1254 PM MDT Sat Jul 18 2026

Upper ridging continues the western CONUS, with several upper waves
approaching the region from the west/southwest. Surface obs show
temps have been lagging in the 70s and 80s, but are now rising
quickly since the low clouds dissipated. Dewpoints are still well
into the 60s across western SD within deep southeasterly flow. Have
dropped max temps today to the low to mid 90s across most locations.
Still looking at some afternoon and evening storms today. SBCAPE of
~1200 J/kg is expected within the corridor from SCentral SD through
the Black Hills into parts of NE WY/NW SD. The next wave is
approaching from NCentral and will cross NE WY/NW SD this evening.
Shear is strongest across NW SD, where southeasterly low level winds
are strongest. Storms are expected to initiate across the Black
Hills this afternoon...then NE WY/SE MT in the late afternoon/early
evening. As storms track into NW SD just north of the Black Hills,
could see a storm or two with gusty winds/hail. These storms will
continue eastward toward a less favorable environment over NCentral
SD, where both instability and shear weaken. The thermal ridge over
the central/northern Rockies will slide eastward overnight tonight
toward the CWA, bringing back very hot temperatures. Highs on Sunday
will be in the triple digits. Dewpoints will be more reasonable
(50s) but will still result in advisory threshold heat index. Will
not make any changes to heat-related headlines. A cold front will
cross MT and push into ND late Sunday, which will result in
strong/severe storms over those areas. By the time the front gets to
NW SD, it seems to stall before resurging southward early Monday
morning. Still unclear with the severe weather threat Sunday
afternoon. It appears the bulk of severe storms will be north and
east of the CWA. Good instability and somewhat decent shear will be
present, but the forcing with the frontal boundary might be missing.
Regardless, could still see convection develop from transient
outflow boundaries or orographically from the Black Hills and
Bighorns. Any storms that develop may be severe, but think better
organization will be limited to areas east of the CWA where
increased forcing/shear will be present. Cooler Canadian high
pressure will build across the northern Plains for the first half of
the week. Uncertain about max temps Monday behind the cold front,
which does seem to struggle pushing out the very warm H85 temps.
Could still be a hot day on Monday, but wouldn`t be surprised if it
ends up being a tad cooler than what the NBM shows. Better cold air
advection is expected Monday night into Tuesday should bring lower
temps...but we`ll likely still see highs in the upper 80s to lower
90s. Better chances for precip are expected for the second half of
next week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Sunday Evening)
Issued At 950 PM MDT Sat Jul 18 2026

VFR conditions are expected to persist across the terminals
through the valid TAF period. An area of showers with embedded
thunderstorms will continue to dissipate over the northern Black
Hills. Light southeasterly winds will become light and variable
through 14z at KRAP and through the TAF period at KGCC.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 9 PM MDT /10 PM CDT/ Sunday for SDZ001-002-
     012>014-025>027-030>032-041>044-046-047-049-072>078.
WY...Heat Advisory until 9 PM MDT Sunday for WYZ054>056-058>060.
&&

$$

UPDATE...GS
DISCUSSION...13
AVIATION...AW