This map is actually a good illustration of how the derecho quickly changed character rapidly as it pushed into the LOT CWA. It went from vortex dominant across DSM/DVN CWA’s, to MV dominant fairly quickly into the LOT CWA. My best guess on why this happened is...For one, the derecho had entered a post-mature stage...Second, the main vortex that moved from north of DSM-Marshalltown-CID eventually weakened as it encountered a disturbed environment from the RFD supercell. At this time it became more MV dominated. .