The tornado that touched down in Dublin on Sunday was unusual but far from unique since New Hampshire generally sees one or two of the twisters each year.

Sunday’s storm had 90 mph winds and was the lowest category of tornado, known as EF1 on a five-point scale. That’s typical for our tornadoes, which are usually on the low end of the scale. The biggest on record passed through the Concord area on July 24, 2008. It created a 50-mile path of destruction, a record for New England.

Determining whether an actual tornado touched down, as compared to other types of dangerous winds, often requires a survey on the ground by the National Weather Service. Part of that involves the direction trees have blown down: If they have fallen in a line, the storm was not a tornado because the twisting funnel of a tornado causes trees to be downed in a splayed fashion.

Tornadoes are most common here when warm air comes up from the south to create a strong shear in which winds change direction as you go up in altitude.