Friday, June 27, 2014

Occurring Now: What is a QLCS Tornado?

When we talk about the vicious twin tornadoes in northeast Nebraska last week, those are "supercell" type tornadoes. Supercell refers to the parent storm. 
There have been at least three tornadoes in northwest Kansas in the last two hours but they are of a different type than what we usually discuss. These are technically called "Quasi-Linear Convective System" (QLCS) tornadoes. For simplicity, I call them "squall line tornadoes."

These tornadoes are not landspouts (a third form of tornado) in spite of what some in the media have reported.

In general, this is the hierarchy of tornadoes:
  1. Supercell tornadoes 
  2. Squall line tornadoes
  3. Landspout tornado
  4. Gustnado 
Most squall line tornadoes are relatively weak: F0 to F1. But, once in a while, they will reach F2-3 and those can cause fatalities (April 27, 2011, in Alabama killed a dozen people that morning). They occur on the leading edge of a line of thunderstorms.  Here is a video of a destructive F-3 squall line tornado in St. Louis on May 31, 2013. 

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