Northwest Arkansas Weather by Meteorologist Rick Katzfey
Radar sequence of tornado supercell thunderstorms that tracked from western Mississippi into southwest North Carolina. (Brian Tang)
Bright reds, oranges and yellows show tracks of where rotation was strongest as detected by NWS Doppler radars during the April 27, 2011 tornado outbreak.
Vertical cross section of radar when tornado was in the vicinity of Tuscaloosa, Alabam on April 27. (@iwitnessweather and The Weather Channel via Twitter )
A satellite loop of the entire outbreak, spanning April 26 through April
28, can be seen in the animation above, also created by NASA. Here’s
the description of the loop, from NASA’s excellent Earth Observatory website:
Thunderstorms can get organized enough to produce tornadoes. Warm moist air gets pulled into the thunderstorm which helps intensify the updraft. The updraft near the back side of the thunderstorm begins to rotate. The rotation becomes strong enough to lower the circulating air to the ground. The jet stream plays an important role in the formation of tornadoes. A thunderstorm needs the jet stream to pull any updrafts away to allow more warm moist air to feed the storm.
Violent tornadoes need an active removal of the air that is being pulled into the storm to keep the rotation active or intensifying. A fast moving jet stream stretches the thunderstorm and quickly removes the top of the updrafts like a conveyor belt removing cool air and replacing it with warm moist air. This action keeps the circulation spinning.
