Wednesday, July 31, 2013

Waterspouts on the Great Lakes

Yesterday's outbreak of waterspouts across Lakes Erie and Ontario developed along a cold front that was moving over the warm lake waters, an event that most often occurs in early fall.  These were "fair weather waterspouts" which form from rising columns of water vapor beneath the developing clouds; spin is produced by wind shear at the leading edge of the front.

Common in both tropical and temperate regions, fair weather waterspouts form from the water surface upward; they tend to be relatively weak and short-lived though they occasionally produce mild damage to marinas or other coastal structures.  As mentioned above, these weather phenomena are especially common on the Great Lakes in early autumn, predecessors of the lake effect snowstorms that follow during the colder months.

Tornadic waterspouts, on the other hand, form within hurricanes and coastal storms or when terrestrial tornadoes move offshore.  Generally associated with severe thunderstorms, these waterspouts form at the base of the cloud layer and move downward; like tornadoes that develop over land, they are powerful and potentially destructive vortices.  Indeed, tornadic waterspouts are responsible for the rare occurrence of fish or frog "rain" as these aquatic creatures are pulled from the lake or sea and fall back to land, often miles from the coast.