Tornadoes can happen in just about any location and at any time, although the chances of having one in late fall and winter are small.
For example, there have been only six tornadoes in Wisconsin during the month of November, and Wisconsin has never recorded a tornado in February.
On average, there have been 21 tornadoes touch down in Wisconsin in a year, with a record 62 tornadoes in 2005. For the 20-year period between 1991 and 2010, there was an average of nine tornadoes in the month of June.
For a tornado to occur, the right weather ingredients must come together in a particular place.
Severe weather requires warm, moist air near the ground and a change in wind speed and direction, or wind shear, with height above the surface.
Weather systems, such as fronts, are also needed to force air upward. Because vertical wind shear is closely related to the presence of a jet stream, tornado season in the U.S. moves north and south during the year.
In the Southeast, the number of tornadoes peaks in March and April, but not until late June and July in the upper Midwest and Northeast.
These conditions have been absent over Wisconsin until last week when tornadoes struck Platteville, Madison and Verona.
On average, this is a rather late start for tornado season.
In fact, 2014 will go down as the sixth latest start to a tornado season and the latest start to a tornado season since 1995. That year had the latest start with the first tornado occurring on June 28.
In 1995 there were less than 10 tornadoes reported, so we can hope for a low tornado count this year, although it is not assured scientifically.
