A Case Study of Nonmesocyclone Tornado Development in Northeast Colorado: Similarities to Waterspout Formation

The evolution of the 26 July 1985 Erie, Colorado tornado is described using data from NCAR's CP-2 Doppler radar. This tornado develops within 20 km of the radar site under weakly forced synoptic conditions and weak tropospheric flow, and is not accompanied by a mesocyclone. The initial circulation forms near the surface at the intersection of two mesoscale boundaries and develops vertically, intensifying into an Fl tornado when it becomes collocated with the intense updrafts of a rapidly developing cumulonimbus. This tornado appears to be the land equivalent of a waterspout, and comparisons between the two vortices are made. It is speculated that Florida and portions of the western High Plains may be prone to nonmesocyclone tornado development, and that vortex-intensification processes associated with nonmesoscyclone tornadoes may be important in mesocyclone tornadogenesis. Suggestions on how to better forecast these tornadoes are also presented.