Severe Thunderstorms North and South of Rapid City

Clusters of severe thunderstorms developed north and south of Rapid City, SD. Eventually, a line of thunderstorms formed once the clusters began to move east-northeastward. The line filled in between the clusters and became severe at times, although the storms wee persistently severe at the northern and southern ends of the line.

The ProbSevere data clearly highlighted the hail threat, with the wind threat also increasing as the line formed and a well defined outflow moved east of the storms. I did notice an increase in the ProbTor percentages for a while with the northern cluster; subsequent analysis showed a brief period of significant rotation at about 6000 feet AGL with lesser rotation on a few scan levels above the 0.5 degree scan. The rotation weakened in about 15 minutes, and the ProbTor levels fell quickly. No tornado was reported nor was a warning issued.

GLM lightning data showed definite flash clusters near the strongest updrafts and overshooting cloud tops, although the parallax in western South Dakota is pretty significant from GOES-16, so I had to use the existing lightning network data and NEXRAD data to get a better idea of storm placement. It will be interesting to see how the eventual GOES-17 data would improve things in that part of the country.

Gary Cannalte