Oklahoma tornado surprisingly quick forming and long lasting
>
http://blogs.physicstoday.org/newspicks/2013/05/oklahoma-tornado-surprisingly-quick-forming-and-long-lasting/
> However, the middle part of the US is called Tornado Alley because it
> is the meeting area of warm, humid air from the Gulf of Mexico to the
> south and cool, dry air from the Rocky Mountains to the west. The two
> masses of air create swirling winds that spawn massive supercell
> thunderstorms. On the day of the most recent tornado, a lot of warm,
> moist air lay near the ground, with a quick drop in temperature as
> altitude increased. And a nearby dissipating storm may have caused a
> surge of low-level air that fed the circulation driving the storm.
> The resulting storm developed incredibly quickly, with the supercell
> forming in 10 to 15 minutes. The tornado itself lasted for 50 minutes
> and traveled for 20 miles, whereas most tornadoes last less than 10
> minutes.