What causes a tornado?

Weather News

CHICOPEE, Mass. (WWLP) – Friday night’s tornado outbreak spanned numerous states and led to dozens of fatalities. But why exactly did these storms pack such a punch, especially in December?

Just for comparison, tornado season peaks in spring and summer, and the average number of tornadoes drops significantly into fall and winter. December tornadoes are not unheard of, but are not extremely common. 

There are a few ingredients necessary for tornado development. A change in wind direction or speed with height, called wind shear, a source of lift and instability, and also moisture. 

Friday night, there were strong southerly winds, and that drew in humidity from the south and created that instability necessary for tornadoes to develop. The storms developed ahead of a cold front, which is that source of lift air is forced upward along cold fronts. 

These tornadoes were also at nighttime, and nocturnal tornadoes are over twice as deadly as daytime ones, since most people are sleeping and aren’t as weather aware. All those factors, in combination with record warm temperatures in the area, came together to create a tornado outbreak for the record books.

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