JOPLIN, Mo. -- The National Weather Service provided additional insight into the decision to rate the tornado last Sunday at the top of the Enhanced Fujita Scale. The tornado was given an initial rating of an EF-4 before it was upgraded the next day.
Bill Davis with the National Weather Service said investigators look at structural damage and how far heavy objects were thrown. This tornado, for example, tossed concrete parking lot "bumpers" that sit low to the ground and can weigh up to 300 pounds.
The NWS investigators also noted that tractor-trailers parked near the Wal-Mart store were thrown farther than 1/8th mile. Manhole covers were also lifted and tossed.
The tornado's path is an estimated six miles long. It's from three-quarters of a mile to a mile wide at some points. The winds are estimated to have briefly hit between 225 and 250mph.