Tornadic Mini-Supercells in Northern Canada

The Canadian Prairies of western Canada are a major portion of the Northern Plains of North America. As such, this region is prone to summer supercells, with over 40 tornadoes reported annually. While many of these storms are large classic supercells, many other events are in the form of "mini-supercells". There are also some tornado events from non-supercell convection.

On July 8, 2004, a large weather system over the western Canadian Prairies produced a wide variety of storm types including one unique tornadic event. In a cool and moist part of this environment, a line of very small thunderstorms developed and tracked from generally east to west. Persistent rotation was observed in virtually every cell within in this line. One of these small storms produced an F1 tornado that tracked through part of the city of Grande Prairie, Alberta. However, this cell escaped detection by the sophisticated algorithms of the Weather Service's Doppler radar system.

Post-analysis of this event demonstrated that this small thunderstorm exhibited mini-supercell characteristics, yet was of a much smaller scale than is typically attributed to this type of thunderstorm.

This presentation will examine radar and other meteorological data from this event and will discuss the implications to the supercell spectrum.