textproduct: Rapid City

KEY MESSAGES

- Isolated to scattered severe storms possible this afternoon through early evening.

- Hotter and mostly dry conditions arrive tomorrow, with hot temperatures continuing into Wednesday.

- Chances for storms increase Wednesday afternoon through early Friday.

DISCUSSION

(This Evening Through Monday) Issued at 104 PM MDT Mon Jul 7 2025

Water vapor imagery this afternoon shows a midlevel disturbance shifting from east to west over the north central CONUS, with enhanced moisture extending from southern MB/ON southwestward thru the Missouri River Valley. This wave is supporting a corridor of elevated convective showers and storms extending westward toward the Badlands. South of this corridor, north to northeast winds indicate a subtle outflow boundary that has pushed south of most of our area outside of far south central SD. Meanwhile, a trailing front can be identified with northwest winds around the Cheyenne River southwestward to along the I-90 corridor in SD and WY.

Cumulus fields at the current hour from south central SD west- southwestward through the Pine Ridge area northwestward into northeastern WY, with a separate area along/behind the front near the Cheyenne River, likely demarcate areas of appreciable surface- based buoyancy. Latest SPC mesoanalysis field suggests a capped 500- 1000 J/kg of MLCAPE paired with effective bulk shear magnitudes of 30-40 kt in these areas. With continued heating, MLCAPE may increase as high as 1500-2000 J/kg in spots, particularly across south central SD ahead of the front. Here, the environment will become increasingly favorable for supercells conditionally capable of all hazards if a discrete mode can become established before the front arrives. Farther west, from southwestern SD through the Black Hills into northeastern WY, slightly weaker deep-layer shear and drier boundary layers (corresponding to higher LCLs) will favor a more transient supercellular mode with low-end severe hail (quarter sized to around ping pong ball sized) and strong to severe winds the primary threats. If any storms manage to develop along the northern Black Hills, a locally favorable environment for all hazards with enhanced MLCAPE, lowered LCLs, and terrain-enhanced shear may favor more rapid storm intensification. Given recent trends, this appears unlikely. The main front will likely cross the area from northwest to southeast by around 03z, bringing a relatively early end to convection and severe potential compared to recent days.

As the trof axis continues to shift eastward, rising heights overspread the region in its wake tonight into tomorrow. Midlevel height ridging and associated low-level thermal ridge building into the area should promote a return of hot and mostly dry conditions tomorrow, though a storm or two cannot be ruled out near the Black Hills/over northeastern WY. HREF mean SBCAPE of 1000-2000 J/kg with deep-layer bulk shear magnitudes of 20-30 kt may support some strong updrafts if initiation occurs. An increasing number of convectively induced potential vorticity anomalies riding atop the ridge over the central/northern Rockies into the High Plains may support more widespread thunderstorm activity by Wednesday despite continued large-scale ridging and warming low-level temperatures. Increased buoyancy but similar/decreased shear compared to Tuesday will be somewhat of a wash in terms of severe potential, but some strong/severe storms may occur.

A pair of potent shortwaves approach the region Thursday into Friday. The first is projected to arrive from the west beginning Thursday morning. The timing of this wave has slowed slightly since yesterday, which would bring it through the area closer to peak heating vs. beforehand, particularly across eastern portions of the area. However, environmental parameter space doesn't look especially suitable for severe weather given marginal deep-layer shear (20-25 kt; LREF probabilities of 30+ kt of 0-6 km bulk shear magnitudes 30% or lower across most of the area). Still plenty of wrinkles to be ironed out, but timing/environmental concerns preclude much confidence in potential for severe hazards. Broader, more amplified trof crosses the region Thursday night through Friday. As cooler air spills into the area behind the initial wave, CAPE will be limited ahead of this second wave as deep-layer shear increases; as such, expecting showery convection with potential for embedded thunder vs. any strong/severe concerns overnight Thursday into Friday. Tightening pressure gradient, pressure rises, and cold air advection behind the associated front will likely bring breezy northwest winds through the day Friday.

AVIATION

(For the 06Z TAFS Through 06Z Tuesday Night) Issued At 1029 PM MDT Mon Jul 7 2025

Mainly VFR conditions are expected through the TAF period. The exception would be MVFR conditions in any storms that develop late Tuesday afternoon.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.