ZCZC SPCSWOMCD ALL ACUS11 KWNS 110431 SPC MCD 110431 MNZ000-IAZ000-SDZ000-NEZ000-110600- Mesoscale Discussion 1953 NWS Storm Prediction Center Norman OK 1131 PM CDT Tue Sep 10 2019 Areas affected...Parts of southeastern South Dakota...southwestern Minnesota...northeastern Nebraska...northwestern Iowa Concerning...Severe Thunderstorm Watch 643... Valid 110431Z - 110600Z The severe weather threat for Severe Thunderstorm Watch 643 continues. SUMMARY...An evolving cluster of storms may continue to pose a risk for strong surface gusts east of Sioux Falls SD, near the western Minnesota/Iowa border area through 1-2 AM CDT. It is not certain that a new severe weather watch will be needed farther east, but trends will continue to be monitored for this possibility. DISCUSSION...Vigorous thunderstorm development persists, southeast and south of a lower/mid tropospheric cyclonic vorticity center which has become increasingly evident in radar imagery, currently east of Mitchell SD. This is also near the nose of a strengthening and gradually veering southerly low-level jet (40-50 kt at 850 mb), but generally to the cool side of the effective warm frontal zone (across southeastern South Dakota) and a southeastward advancing outflow boundary (across north central Nebraska). Low-level shear is strong ahead of the convective outflow across southeastern South Dakota, where modest near surface easterlies veer to southerly and southwesterly aloft. However, north of the surface front, near surface thermodynamic profiles are cool and stable to surface-based convection. The risk for tornadoes appears low, but the environment may be conducive to strong surface gusts as activity spreads east of the Sioux Falls area, near the western Minnesota/Iowa border area through 06-07Z. This leading convection has been advancing eastward roughly with the modest 20-30 kt westerly deep-layer ambient mean flow, but some eastward acceleration is possible during the next couple of hours. ..Kerr.. 09/11/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MPX...DMX...FSD...OAX... LAT...LON 44089630 44149577 44019490 43469464 42879561 42609687 42569745 42949775 43469742 43799736 44089630 NNNN