why don't tornados ever strike large cities?

They do Salt Lake had one hit. There are others but it is not as frequent because if you add up the square miles of large cities versus the square miles that are not in big cities there is a lot less city than not. Also the building somewhat disrupt normal air currents.

That’s what Hurricanes are for….

It seems people just never really built large cities in tornado prone areas, just earthquake hot spots

But seriously, big cities go up where there is potential for big commerce. That’s not really possible in the mid-west. Trailer parks however are very viable for somewhere with almost no economical backbone.

Wow, spargett. You underestimate the Midwest. How about Chicago, Milwaukee, St. Louis, Minneapolis-St. Paul?

Now this sounds stupid, but they hardly ever touch down in huge cities by the grace of God. Could you imagine? It would certainly bring out the prayer in me! And I am agnostic so that says A LOT! I agree with gooch.

CHECK OUT TORNADO ALLEY
Some people have asked if tornadoes appear everywhere in tornado alley. The fact is on all tornado alley maps there are areas that have never had a tornado hit there.
remember, not every city in tornado alley has been struck by a tornado while others have had many tornadoes hit them.
http://www.tornadochaser.net/tornalley.html

First, the idea that a tornado can’t hit a big city is one of those dangerous myths that can be deadly. Similar myths say that a river, a lake, a hill, or some other kind of landscape protect certain places from tornadoes. Strong tornadoes come from huge thunderstorms that go where the upper-altitude winds push them, including across cities. As you note, a tornado hit downtown Nashville, Tenn., earlier this spring. (Information on that and other 1998 twisters is in our weather and climate of 1998 index.)
http://www.usatoday.com/weather/resources/askjack/watorsaf.htm

The downtown areas of “big cities” have had tornadoes on occasion. This past spring, a tornado passed through Miami, Florida before it moved out to sea, disproving the idea that they can’t form in cities. The St. Louis, Missouri and East St. Louis, Illinois areas have had more than their share of tornado strikes to their downtowns.
http://www.tornadoproject.com/myths/myths.htm

Excellent page / description
Tornadoes occur just about everywhere in the world, from India to Australia, and all over the United States, but the most famous and active breeding ground for tornadoes is Tornado Alley. It extends from Texas up through Oklahoma, Kansas and Nebraska to the Dakotas.
http://skydiary.com/kids/tornadoes.html

The National Weather Service confirmed at 5:12 p.m. that a tornado touched down in Bay Ridge, Brooklyn, this morning. The tornado was classified as a 2 on the Enhanced Fujita scale, which goes from 0 to 5. An EF2 tornado consists of winds of 111 to 135 miles per hour.
http://cityroom.blogs.nytimes.com/2007/08/08/brooklyn-storm-is-declared-a-tornado/

Raleigh, NC was decimated by tornadoes back in the early 80’s. I remember driving to work along a major thorough-fair and seeing houses with the back walls ripped off, leaving everything inside still in place. The K-mart was a pile of rubble. I was mesmerized by a copse of pines – they were all (hundreds and hundreds of them) snapped off at exactly the same level, about 20 feet off the ground. There was no sign of the tops, just this forest of straight trunks.

@deepseas I guess we need to know the definition of a “big city” because there are plenty of cities that get hit by tornadoes. I live just outside of Memphis, TN, which has about 650,000 people living in it and it was hit pretty bad in a couple of areas. Its all about location and weather patterns. Not to mention Jackson, TN, which is smaller, but it’s not completely “rural”.

I’m thinking primarily of large “skyscraper” areas

its the law of average, I guess. Since there are fewer “big city” areas according to your definition, the chances of a tornado hitting them is less than those of “small cities”.

@deepseas…..How about a little town called Atlanta?

http://www.cnn.com/2008/US/03/14/storm.atlanta/