Observations of the Interaction of a Tornadic Mini Supercell with a Preexisting Meso-Gama Surface Boundary

Moist convection produced a brief miniature supercell tornado east of Denver, Colorado during the afternoon of 4 October 1998. The tornado appears to have developed concurrently at the time the convection 1) interacted with a preexisting surface boundary, and 2) quickly evolved up-scale, exhibiting radar characteristics suggestive of a miniature supercell. The convection initiated off the Front Range of the Rocky Mountains, west of Denver, in an environment of moderately steep lapse rates near the center of a seasonally strong short-wave trough. Based on the 00 UTC KDNR sounding, the background atmospheric environment was one that appeared hostile to tornado development: CAPE ~ 460 J kg^-1, LFC ~1000 m AGL, negative 0-3 km AGL storm relative helicity, EHI 0.1. Radar analysis indicates that the updraft exhibited weak mid-level shear in the vertical a full 30 minutes before the cell interacted with the surface boundary. Once the apparent interaction between the convection and boundary commenced, the miniature cell developed and maintained supercell characteristics. The cell retained these characteristics for nearly 60 minutes as it moved continuously along the boundary before dissipating.