July 17 featured a persistent boundary across eastern Adams, Arapahoe and Elbert counties in Colorado with deepening moisture on easterly flow. Shear was marginal, but with the boundary in place and strong instability, storms developed along the boundary and two of them spun pretty strongly, causing the NWS to issue tornado warnings on them. We caught them as the intensified and produced a couple of funnels, although we never could confirm touchdown. The one pictured above appeared to be anticyclonic as it formed on the south side (looking west) of the clear slot of this rotating storm.

2006, Colorado, July 2006, lightning