Mesoscale Discussion 1929
Issued: · Valid: –
Summary
Widely scattered thunderstorms capable of producing large to very large hail and severe wind gusts are expected this afternoon across portions of western South Dakota and southwestern North Dakota. These storms may also include the potential for brief tornadoes.
Product Text
000 ACUS11 KWNS 111914 SWOMCD SPC MCD 111913 SDZ000-NDZ000-112115- Mesoscale Discussion 1929 NWS Storm Prediction Center Norman OK 0213 PM CDT Tue Aug 11 2026 Areas affected...portions of western South Dakota and southwestern North Dakota Concerning...Severe potential...Watch likely Valid 111913Z - 112115Z Probability of Watch Issuance...80 percent SUMMARY...Widely scattered thunderstorm development is expected this afternoon across portions of the western Dakotas. A supercellular storm mode is likely, with the primary threats large to very large hail and severe wind gusts. DISCUSSION...Recent visible satellite imagery depicts agitated cumulus developing along the Black Hills in western South Dakota. Widely scattered thunderstorm development is likely across this region and within a weak surface confluence zone noted just west of the ND/SD/MT border. The 18z UNR observed sounding sampled 2000 J/kg MLCAPE and steep mid-level lapse rates of 8-9 C/km, with further destabilization expected through the afternoon (MLCAPE forecast to exceed 3000 J/kg by peak heating). Enhanced westerly flow aloft is also yielding elongated, relatively linear hodographs and 40-50 kts of effective shear, which will support splitting supercells. Ample buoyancy within the hail growth zone, steep mid-level lapse rates, and a favorable storm mode will promote a threat for large to very large hail of 2-3+ inches in diameter. Isolated giant hail (4+ inches in diameter) cannot be ruled out with any persistent, longer-lived supercell; however, supercell longevity remains somewhat uncertain. Severe wind gusts and perhaps a brief tornado are also possible. While the exact timing of convective initiation is uncertain, a Severe Thunderstorm Watch will likely be needed within the next 1-2 hours to cover this potential. Some recent CAM solutions also indicate some potential for upscale growth later this evening; however, this scenario remains unclear. Should this occur, a transition towards damaging wind gusts as the primary threat could be expected. ..Chalmers/Hart.. 08/11/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ABR...BIS...UNR... LAT...LON 43670380 44270382 45380379 46210362 46710300 46810243 46770204 46680185 46390149 45990126 45050118 44130123 43690131 43350154 43140196 43100233 43090289 43240340 43670380 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN