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2/04/2007

Supercells: tornadoes that last

Earth News: Florida, USA
Feb 03, 2007

It was the MOST POWERFUL TORNADO TO HIT THE STATE IN NEARLY A DECADE. They call it a supercell - an especially deadly type of tornado that RARELY strikes the state. Supercells last longer than other kinds of tornadoes, which is why this twister stayed powerful enough to rip across three Florida counties. It reached 140 to 150 mph. Some UNUSUAL WEATHER PATTERNS that may be related to El Nino helped create the explosive combination of wind, moisture and low pressure that spawned the storm. The story of this tornado began with high winds in the upper atmosphere. The "disturbance" of winds churned so swiftly that it created an area of low pressure below it, near the surface of the Gulf of Mexico, south of the Mississippi-Alabama border. Wide bands of wind began swirling around this low-pressure center, in the same counterclockwise motion you see when watching satellite images of a hurricane. These bands scooped up warm, moist air from the tropics and shoved it toward Florida. Meanwhile, winds rushed across Florida toward the low-pressure zone, smashing into the twirling center and pushing the winds higher by sheer force. Tornadoes often die shortly after the warm, moist air starts to shoot skyward. Sometimes falling rain cools off the warm air below and stops it from rising, But in this case, high-level winds called jets streaked across the top of the storm. This action helped to spin the tornado, and also acted like a suction pump to keep the updraft going. "Normally, on the average, the structure of that jet doesn't make it this far south." So what caused the high-level winds? They can zip across Florida during El Nino years, when the powerful jet stream tends to flow farther south than in other years. Meteorologists tracked the potential for a storm for a couple of days, seeing that a "disturbance" of winds in the upper atmosphere was traveling toward Florida, where there was a mass of warm air nearby. "Two days ago we kind of looked at this and said, 'Hmm, this looks interesting.' Yesterday we looked at it and said, 'Uh-oh.' " The past strong El Ninos, in 1998 and a similar one in 1983, coincided with the two most active tornado seasons in Florida history. Note: Opinions published by the St.Petersburg Times in relation to climate (El-Nino) phenomena do not in anyway reflect the opinions of Skywatch-Media. This report is published for informational purposes only.
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