textproduct: Rapid City

KEY MESSAGES

- Isolated severe thunderstorms possible this afternoon and evening, with a corridor of overnight thunderstorms expected from northeastern WY through the Black Hills onto the western SD plains.

- More widespread strong to severe storms are possible tomorrow, mainly near the Black Hills and across southwestern/south central SD.

- Hotter and drier Tuesday into Wednesday.

- Stronger midlevel disturbance arrives Thursday into Friday, bringing a return of unsettled conditions and severe weather potential.

DISCUSSION

(This Evening Through Sunday) Issued at 108 PM MDT Sun Jul 6 2025

Water vapor imagery this afternoon shows a fairly dry airmass over the area in the wake of a disturbance that brought convection to much of northeastern WY and western/central SD last night into this morning. A few attempts at convective initiation near the Bearlodge Mountains have largely dissipated, though a cumulus field continues to bubble over the Black Hills with occasional signs of congestus and/or towering. An area of increasingly agitated cumulus is also evident across southwestern SD in the vicinity of a convergent baroclinic zone. Upstream, water vapor indicates a shortwave trof shifting eastward from southern AB into SK and separate, broad ascent over the central Rockies/Four Corners. No other appreciable areas of large-scale ascent are evident across the region.

Some environmental recovery has occurred, and will continue to occur, this afternoon across southwestern and south central SD in the wake of morning convection, though confidence is low in the extent of this recovery. 12z HREF members range from near zero to over 2000 J/kg of SBCAPE by 20z from the Pine Ridge eastward thru the Sandhills, which is running a bit ahead of current SPC mesoanalysis. If the low-level thermodynamic environment recovers sufficiently, any storms that develop across our southern tier of counties would be capable of severe hazards given accompanying midlevel lapse rates exceeding 7 C/km, effective bulk shear magnitudes of 35-40 kt, and 0-3 km SRH values of 100-200 m2/s2, all of which would combine to promote supercellular modes. For now, higher confidence of CI and, accordingly, severe weather, is south of the NE/SD border. Over the Black Hills and Bearlodge Mountains, an uncapped profile with steep low-level lapse rates should continue to support isolated/scattered attempts at CI this afternoon, which could lead to some showers/storms. However, a midlevel weakness in lapse rates and relatively weak deep-layer shear (albeit stronger low-level shear compared to yesterday) will limit overall intensity and severe potential. Still, cannot rule out an isolated updraft or two capable of marginally severe hail.

Tonight, similar to last night, isentropic ascent atop the baroclinic zone should promote a roughly west-to-east oriented zone of convection somewhere in the vicinity of the Black Hills eastward onto the SD plains. Mean MUCAPE around 1000 J/kg and deep-layer shear of 20-30 kt per the 12z HREF suggest that storm organization may be limited, with the predominant mode likely being multicells. However, locally stronger/transiently rotating updrafts may be capable of small to marginally severe hail. The other concern will be the potential for locally heavy rainfall and/or training storms, particularly if the storms occur in a similar corridor to areas where 2-3" of rain fell last night (approximately central Crook Co. eastward through Tilford/Piedmont area). With PWATs remaining 125- 150% of normal, cannot rule out torrential downpours and, if training occurs, localized flash flooding.

Late tonight into tomorrow, potent low-level/midlevel frontogenesis along an attendant trof, possibly aided by outflow from overnight convection, will travel southeastward thru the region. Timing of the trof passage and associated frontogenesis will play a large role in location of any storms/severe potential tomorrow afternoon. Ahead of the front, SBCAPE will likely climb to 2-3 kJ/kg by early to mid afternoon. Coupled with 35-45 kt of shear, the environment will surely be suitable for strong to severe convection. Favored mode in 00/12z HREF members is for discrete supercells early, with activity congealing into an MCS/QLCS later in the afternoon/evening. However, with such strong linear forcing, discrete storms may be hard to come by outside of the Black Hills, where local, terrain-driven forcing may first support CI. Subjectively, most time-lagged members of the 12z HREF (i.e., 00z or 06z runs) suggest more widespread severe potential compared to the 12z members, indicating that there may be a slight downward trend in expectations for our area per CAMs. But, the pre-trough environment is nothing to sneeze at, so will run with the anticipation of severe potential along and ahead of the boundary.

Behind the low-level trof, deep Q-vector divergence overspreads the region, followed by rising heights into Tuesday. These height rises and associated strengthening capping should largely preclude convection on Tuesday as temperatures rise into the 90s for most. Low-level thermal ridging further expands northeastward into the north central CONUS on Wednesday as a trof takes shape to our west, which should allow temperatures to rise a few more degrees. By Wednesday afternoon/evening, subtle convectively induced shortwave disturbances may be sufficient to produce at least isolated storms despite broader midlevel ridging over the region. Come Thursday, a pair of disturbances take aim at the area, one a quick-hitting, compact shortwave and the second a more amplified and longer-wave trof. These disturbances will likely support more widespread thunderstorm activity, some of which could be severe, followed by an arrival of milder temperatures heading into the end of the week.

AVIATION

(For the 18Z TAFS Through 18Z Monday) Issued At 1150 AM MDT Sun Jul 6 2025

TSRA will redevelop this afternoon, but will be more limited in coverage. Gusty, erratic winds will still be possible near any storms. Precip maybe linger tonight, especially around the Black Hills.

UNR WATCHES/WARNINGS/ADVISORIES

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