Why This Tornado Season Has Been a Mild One

Tornado season this year started off with a bang — an above-average number of twisters churned across the United States in the early months of 2012 — but lately, the storms have been more subdued.
And this spring hasn't seen the terrible twisters that devastated parts of the country last year.
So what's behind the quieter spring? Thank the jet stream, weather experts say.