Ranking Tornadoes on the EF scale

The Enhanced Fujita (EF) damage scale is used by the National Weather Service to classify tornadoes based on the severity of damage they leave behind. Two of the tornadoes that occurred on Friday night, June 19th were rated EF2 based on damage to structures and extensive tree damage. One of the EF2 tornadoes partially unroofed a home in Allegan County while the other EF2 took the roof and deck off a house northwest of Richland in Kalamazoo County. Extensive roof damage to residential homes is a damage indicator for winds in the EF2 range, which is defined as 111 mph to 135 mph. For more information on the original Fujita Scale and the Enhanced Fujita Scale click here.

Although these tornadoes were ranked EF2, their top winds were estimated to be around 115 mph, which is on the lower end of the range. Therefore, they did not produce the extensive damage of some previous tornadoes of that magnitude. The EF2 Williamston Tornado of October 18, 2007, which was estimated to have had top winds of 130 mph, damaged or destroyed dozens of homes along a 17 mile long path during its lifespan of nearly half an hour. In contrast, the Allegan County EF2 lasted about 9 minutes and covered less than 6 miles. The Kalamazoo County EF2 was even more brief, lasting only two minutes and producing a damage path of only one and a quarter mile. Both tornadoes produced their EF2 damage over very small areas, only on the order of tens of feet.

The Williamston tornado was spawned by a long-lived supercell thunderstorm. The tornadoes of June 19th were not related to these powerful thunderstorms, but were more likely the result of outflow boundaries interacting with multi-cellular thunderstorm updrafts. Therefore, the tornadoes spun up and dissipated rather quickly, making it very difficult to issue tornado warnings for these storms. Fortunately, most of the tornadoes that form this way are not as strong as supercell tornadoes. The EF2 damage from the non-supercell tornadoes of June 19th was rather unusual.

This drives home the point that thunderstorms are capable of producing tornadoes with little or no advance warning. In fact, the majority of the tornadoes that occur in Michigan last less than 15 minutes. It is always a good idea to take shelter in a sturdy building when strong thunderstorms are occurring, even if no watch or warning is in effect.

 



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