283
FXUS63 KUNR 012317
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
517 PM MDT Tue Jul 1 2025

.KEY MESSAGES...

- Hot with isolated storms through Thursday

- Scattered to numerous possible from west to east late Thursday
through the holiday weekend

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 201 PM MDT Tue Jul 1 2025

A broad upper level trough is centered over the Central Plains,
bringing warm and dry conditions to the region. A weak shortwave
trough will move through the Northern Plains late this afternoon and
tonight, potentially bringing isolated showers and thunderstorms to
the forecast area. The ridge will persist though Thursday, leading
to continued above normal temperatures. An upper level trough is
expected to dig into the Pacific Northwest later this week, which
will begin to erode the ridge and bring a chance of more widespread
precipitation and cooler, but still near average, temperatures for
the weekend.

For this afternoon and tonight, the cap is eroding across the
forecast area with only about 50 J/KG of CIN left to overcome. As
the weak shortwave progresses through the area it will eventually
interact with the low level moisture that is advecting into the area
with the southeasterly winds and marginal shear of 30 to 40 kts,
resulting in the potential for isolated strong to severe storms. The
primary threat will be large hail with any storm that does develop.
The convection looks to remain ongoing overnight toward central
South Dakota closer to the influence of a strengthening low level
jet and warm air advection along a developing warm front.

Thermal ridging continues to build eastward Wednesday and Thursday.
On Wednesday, highs will be in the 80s and 90s for most. As the low-
level thermal ridge expands eastward, the midlevel ridge axis also
shifts overhead Wednesday afternoon, which could again limit
convective initiation. Convection will be further complicated by the
best corridor of surface dew points being shunted northeastward as
the low-level thermal ridge expands eastward, thus decreasing
buoyancy in locations that would otherwise benefit from easterly
upslope flow in the pursuit of overcoming the cap. Altogether,
coverage again looks spotty at best, CAPE values potentially
exceeding 2000-3000 J/kg coupled with deep-layer shear of 35-40kts
would suggest that if the cap breaks, severe weather could occur.

Thursday continues to look like the warmest day of the week, with
triple digit highs across west central SD. By Thursday afternoon and
evening the ridge axis will be east of the area. Falling heights, a
frontal boundary sagging southward from Montana/North Dakota, and Q-
vector convergence will all likely lead to some convection.
Depending on timing of waves embedded in the flow, could see
scattered to numerous storms through the holiday weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 515 PM MDT Tue Jul 1 2025

TSRA this evening will be concentrated over southern SD, where
large hail and strong erratic winds may occur along with IFR
conditions. Additional storms may occur this evening into the
overnight hours, especially over northwestern SD. Outside of
storms, VFR conditions are expected.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Helgeson