Snowspout

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Rare snowspout seen over Lake Ontario from Whitby Ontario, January 26, 1994

A Snowspout is an extremely rare meteorological phenomenon in which a vortex resembling that of a waterspout forms under the base of a snow squall. The term snowspout is used to differentiate between a common warm season waterspout and the rare winter season waterspout which will often form in temperatures of -18C (-0.4F) or colder. Very little is known about this rare phenomenon and only six known pictures of this event exist to date, four of which were taken in Ontario, Canada.

[edit] Environmental Conditions

There are three critical criteria for the formation of a Snowspout:

Extremely cold temperatures present over a body of water warm enough to produce fog resembling steam above the waters surface, this usually requires temperatures of -18C or colder if the water temperature is no warmer than 5C.
Lake effect snows in a clustered or banded formation must be present and on going.
The synoptic or environmental winds must be extremely light; usually less than 5 knots (9.25 km/h) will suffice.