Why the big-city tornadoes?

I saw an article last week on Accu-Weather's website about 2011 being the year of urban tornadoes.

Alex Sosnowski, who wrote the article, attributed the large number of tornadoes in populated areas this year to chance, an eastward shift in the springtime jet stream, and the growth of populated areas.

The first of those reasons is obvious -- bad luck.

The jet stream that carried storm systems this spring crossed the South in April and early May, then moved northward later in May. Typically, that air current passes over the Great Plains during the spring, bringing twisters to the so-called Tornado Alley.

Instead, the twisters hit Texas, Arkansas, Tennessee, Mississippi, Alabama, Georgia, the Carolinas and Virginia early in the season, then slipped northward across Missouri, Illinois, Indiana, Ohio, Pennsylvania, New York and Massachusetts afterward.

All of those 15 states have heavily populated areas, and killer tornadoes struck populated areas like Tuscaloosa, Birmingham, Dallas, Jackson, Bristol (Va.), Raleigh, Joplin (Mo.), and Springfield (Mass.), among other places.

I wrote earlier this year -- strangely, just a few days before the Raleigh-area tornadoes -- that twisters sometimes strike populated areas. In many people's minds, tornadoes are a rural event, and that's because they're so common in the sparsely populated areas of the Midwest.

Looking back through the archives, here are a few other killer storms that struck populated areas:

-- A tornado in May 1840, killed 340 people in Natchez, Miss. At the time, Natchez was still a major trading center in the region. Most of those killed (269) were on flatboats in the Mississippi River.

-- In May 1896, a tornado ripped through St. Louis, killing 255. Officials say the death toll might have exceeded 400, with many people being killed on boats in the Mississippi River. But their bodies were never found.

-- A June 1953 twister in Flint, Mich., left 115 dead.

-- And the day after the Flint tornado, a twister in Worcester, Mass., had a death toll of 94. Tornadoes aren't common in Massachusetts, but the 1953 storm and the twister last week are proof that they can take place anywhere (yes, there's even been a tornado in Alaska).

You can find Alex Sosnowski's article here.