document: 1990 is fast becoming one of the worst years on record for tornadoes and flooding across the middle and southern sections of the nation . So far this year , 726 tornadoes have touched down nationwide , well ahead of the 640 tornadoes recorded during the first six months of last year , and the 30-year average of 482 tornadoes recorded between January and July , said Frederick Ostby of the National Severe Storms Forecast Center here . The nation had 747 tornadoes in the first six months of 1973 _ one of the biggest years for tornadoes since 1950 , when the forecast center began keeping reliable records of the storms . There were 756 tornadoes reported in 1982 . `` We seem to be on a pace that would put us up with those two years , '' Ostby said . The culprit in this tornado barrage across the Plains is a persistent West Coast pattern of low pressure in the upper atmosphere that is keeping the jet stream anchored at a southern latitude . This year 's storms seem particularly violent , as illustrated by the March 13 tornado that cut a swath a mile wide and brought winds of 300 mph to a field in Kansas . The tornado was the strongest to hit the United States since 1985 . The first weekend in June saw the worst outburst of tornadoes since 1974 . Ostby said 101 tornadoes touched down from Kansas to Kentucky , leaving nine people dead . But a break in the storm pattern may be at hand . As summer wears on , the land warms up and cold air from Canada retreats . This moves the boundary of the jet stream to the north , Ostby said . `` Our longer range computer forecasts are suggestive of that . There is some kind of a readjustment beginning to take place in the upper atmosphere , '' he said . However , a study of tornado trends indicates parts of the Midwest , particularly Kansas and Missouri , are heading into a six-year period of more intense tornadoes . The study of tornadoes since early this century shows that they are concentrated in regions for five - or six-year periods , said Michael Smith , president of WeatherData Inc. . But warning of impending storms is becoming more sophisticated , leading to fewer deaths . Tornadoes have caused 20 deaths this year , while an average year in the 1980s saw 52 deaths , and in the 1970s nearly 100 , Ostby said . `` There are better watches , better warnings and a better response , '' Ostby said . Ostby credited the quicker response to computers that allow meteorologists to see many sources of data , such as satellite readings , more clearly . Flooding in the South and the Plains has been as destructive as the tornadoes . The death toll from last week 's flash floods in Shadyside , Ohio , rose to 21 on Monday , making the flood one of the most deadly in recent years . Authorities held out little hope for more than a dozen others listed as missing . Wegee and Pipe creeks overflowed during storms that dumped 5 -LCB- inches of rain in 3 -LCB- hours . The floods destroyed as many as 70 houses and damaged up to 40 , officials said . Flooding in Texas has been blamed for at least 16 deaths since April . An estimated 10,000 people were forced from their homes , and high water caused hundreds of millions of dollars in damage .
extractive_keyphrases: tornadoes tornado trends flooding storms damage deaths study