The green line shows the linear trend of tornado numbers implying that April 2011 would be expected to have about tornadoes. Overall the decadal averages have been increasing with the exception of the 1980s. That single year drove the 1970’s decadal yearly average to 124.Ģ. The 1974 outbreak along with additional tornadoes that month brought the greatest number of tornadoes reported in April that year to. Monthly Totals of April tornadoes from 1950 to 2010 from NOAA’s SPC.ġ. tornado season) as storm systems become energized with contrasts of lingering winter cold and invading spring warmth clashing during thunderstorm formation accompanying midlatitude cyclones.įigure 1. The spring month of April is traditionally among the most active (with May typically being the peak of the U.S. (The warning of an impending or a virtually occurring event is issued by your local National Weather Service office.)įigure 1 from the SPC shows the monthly totals of April tornadoes from 1950, when reliable numbers became available, through 2010. thunderstorm or tornado watch, is issued when meteorological conditions are favorable for that weather situation to occur. The SPC provides severe thunderstorm and tornado watches for the contiguous U.S. The NOAA Storm Prediction Center (SPC) is one of NOAA’s National Centers for Environmental Prediction. At a commemoration event twenty-five years later, a National Weather Service official noted, “We want the public to be aware that deadly storms such as the 1974 outbreak can and will happen again, and we want people to be prepared.” ( ( )) Unfortunately, the tornado episodes of spring 2011 demonstrated that these deadly tornado threats will always be with us. There were 330 deaths and almost 5,500 injuries. These storms proved very strong, long-lived and deadly. During a sixteen-hour period, 148 tornadoes swept across thirteen states. But that was just the prelude, as April 3 and 4, 1974, saw the greatest outbreak of tornado death and destruction to that date in the United States. That year over 1100 tornadoes were reported. The year 1973 was an exceptional year for tornadoes. Explain why winds on one side of a tornado may be stronger than winds on the other side.Describe the general weather conditions favorable for formation of tornadic thunderstorms.List some of the characteristics of the path of an intense tornado.The special weather pattern required for tornadic thunderstorms to develop is most common in spring and summer in the central United States.Īfter completing this investigation, you should be able to: In the Northern Hemisphere the rotating vortex generally exhibits a counterclockwise circulation as seen from above. Most tornadoes are spawned by and travel with severe thunderstorms. It was updated to the enhanced scale based on additional research. Theodore Fujita of the University of Chicago developed the original scale in 1971. Wind speed in a tornado, estimated from the extent of property damage, is the basis for rating these systems from 0 (weakest) to 5 (strongest) on the Enhanced Fujita scale (EF-scale). Its extreme winds can take lives and cause considerable property damage. A tornado can produce the most intensely violent weather conditions on Earth.
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