SPC MD 749

MD 0749 CONCERNING SEVERE POTENTIAL...TORNADO WATCH LIKELY FOR SOUTHEAST SD...NORTHEAST NE...NORTHWEST IA...AND SOUTHWEST MN Mesoscale Discussion 0749 NWS Storm Prediction Center Norman OK 0111 PM CDT Sun May 17 2026 Areas affected...southeast SD...northeast NE...northwest IA...and southwest MN Concerning...Severe potential...Tornado Watch likely Valid 171811Z - 172015Z Probability of Watch Issuance...95 percent SUMMARY...Severe potential will increase over the next couple of hours across southeast South Dakota and northeast Nebraska into adjacent portions of Minnesota and Iowa. A substantial all-hazards severe risk is expected by mid-afternoon into this evening. Very large hail to 3.5 inch diameter, strong tornadoes, and intense wind gusts to 90 mph appear likely. A tornado watch will likely be issued by 19z to 20z. DISCUSSION...A cluster of elevated convection is ongoing across north-central NE ahead of the surface cold front. The downstream airmass is quickly destabilizing as rich boundary-layer moisture (mid to upper 60s F dewpoints) spreads north and west amid strong heating. Immediately downstream from the ongoing thunderstorm cluster, latest mesoanalysis indicates weakening midlevel capping. This is supported by increasing cumulus from Brown to Knox and Antelope Counties in NE in the vicinity of a quasi-stationary boundary/warm front. Increasing midlevel southwesterly flow is evident in the past couple of hours on region VWP. This trend should continue, with additional strengthening of low-level flow in response to surface pressure falls. Vertically veering wind profiles with 40+ kt effective shear magnitudes within moderate to strong instability (by mid/late afternoon) will support robust supercell development within the warm sector on the nose of the midlevel dry slot across the northeast NE vicinity. Discrete supercells will pose a risk for very large hail, strong tornadoes, and damaging wind gusts. Additional linear convection is expected along the cold front, particularly across SD into southern MN. Given favorable low-level shear, line-embedded cells/mesovortices will pose a tornado risk even in linear convection. As linear convection organizes and a low-level jet increases toward late afternoon into the evening, a substantial damaging wind risk may evolve. ..Leitman/Mosier.. 05/17/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX...FSD...OAX...GID...LBF...UNR... LAT...LON 41509588 41419680 41489786 41779924 42209988 42570005 42989990 43169978 43529913 44229752 44329681 44329625 44229587 43959537 43419522 42589536 41979555 41509588 MOST PROBABLE PEAK TORNADO INTENSITY...120-145 MPH MOST PROBABLE PEAK WIND GUST...75-90 MPH MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN Read more