The record annual number of EF-4 and EF-5 tornadoes occurred in 1974, when 36 such tornadoes scarred the landscape of the Midwest and Great Plains.Tags: Application Essays To Nursing SchoolReasons For Writing A Business PlanCollege Essay PapersAction Research Case Study MethodologyArgument Essay For PizzaOur School Trip EssayEssay On Being Left HandedHow To Make An Assignment
S., although not by a sufficient amount to make it distinguishable from natural variability, at least not yet.
Computer-model projections of how instability may change in the future, though, show that this tornado ingredient is likely to increase because of warming surface temperatures and the addition of moisture in the air through evaporation.
That increase in atmospheric instability could boost the number of days with severe thunderstorms in parts of the U. One study, published in the Proceedings of the National Academy of Sciences in 2007, found that a doubling of greenhouse gases in the atmosphere would boost the number of severe thunderstorm days in parts of the U.
S., particularly in the Southeast and along the East Coast.
Similarly, there is no evidence to indicate that EF-4 and EF-5 tornadoes — like the one that decimated a large swath of Moore — are becoming more frequent or severe.
Such tornadoes are rare — they comprise less than 1 percent of the total number of tornadoes — yet they are the most reliable killers, accounting for 70 percent of tornado fatalities.
Tornado statistics show that the Oklahoma City metro area has had the most direct tornado hits of any American city, with at least 100 since 1890.
That's according to the Storm Prediction Center in Norman, Okla., which is situated just down the road from Moore, and whose forecasters were forced to take shelter as the storm moved through.
Instead, an increase in tornado counts of EF-0 or stronger tornadoes has been attributed to an uptick in observations of very weak tornadoes.
The Enhanced Fujita Scale measures tornado strength based on the extent and type of damage that they cause (no surface weather station has ever survived a direct tornado strike to take wind measurements from inside a twister).