After their first survey of tornado damage in far northern Iowa, the National Weather Service in Sioux Falls ranked the tornado that cause serious damage in Sibley, IA an EF-4. That’s the second highest level on the Enhanced Fujita Scale. The supercell first developed in Western Nobles County, Minnesota before moving into far northern Iowa.
The storm then produced a tornado that caused significant damage in the Little Rock and Sibley areas.. Several buildings and homes sustained major damage. A survey team from the National Weather Service reports the strongest damage occurred just southwest of Sibley. There is little other information yet including the estimation of the tornadoes’ winds. The NWS expects to release more information in the coming days, likely including pictures and a map indicating the exact track of this monster tornado.
But based on the classification of this tornado as an EF-4, we can tell you the winds were somewhere in between 166 and 200mph. This is an extremely violent tornado and it’s amazing news that no one was hurt or killed. Below is a chart showing the wind speeds estimated by the Enhanced Fujita Scale.
|Scale||Wind Speed||Annual Occurrence|
|EF-5||200mph+||less than 0.1%|
Not only does this graph show you the wind speeds associated with an EF-4 tornado, it also shows you how rare these tornadoes are. Each year, an average of 0.7 percent, that’s less than one out of every hundred tornadoes are as powerful as the tornado that hit northern Iowa Friday Night. A very rare event and one not seen in Iowa since the monster EF-5 tornado that hit Parkersburg and New Hartford on May 25th, 2008.
We’ll bring you more on the damage survey in northern Iowa when it becomes available later this week.