Tornado Tracks

John Nelson has created a beautiful map of all the tornado tracks in the United States from 1950 to 2006, using NOAA data from Data.gov.

Not only is Nelson’s map nice to look at, but some interesting patterns reveal themselves. The first thing that jumped out at me was that the orientation of the tracks was far from random. In fact, the lines are oriented with overwhelming predominance diagonally, from Southwest to Northeast.

This will not be a surprise to any weather or storm experts, but it was to me. The pattern is confirmed (for example) in this paper (pdf) — see, for instance, their Figure 2. Here we learn that the direction of the tracks (not shown on Nelson’s map) is predominantly towards the Northeast. There is more than one factor explaining the regularity, but the main reason seems to be simply the predominant winds, which convect the storms that give rise to the tornadoes.