Spring in North America brings not only new flowers, but a new crop of tornadoes. The 2011 tornado season has already been horrific, and our hearts go out to all those affected. Like most natural phenomena, tornadoes exhibit a spatial pattern on a global, regional, and local scale, and a temporal pattern depending on season, time of day, and duration. Both the spatial and temporal components can be examined and understood with the use of GIS.
To do this, I have written three lessons and compiled data sets that may help do just that. The first, Investigating Historical and 1 Modern Tornado uses ArcGIS Online (http://www.arcgis.com, search on “Tuscaloosa owner:jjkerski”) to examine pre- and post-tornado imagery that can be toggled on and off or adjusted in terms of opacity. Using these sobering data sets, the width and length of the Tuscaloosa tornado can be examined, as well individual building types affected, and historical tornadoes by decade throughout the USA. The second, “Investigating Historical Tornadoes Using ArcGIS”, allows for further investigation, which reveals that while more common on the Great Plains and interior lowlands, tornadoes have occurred in nearly every state, and are not as uncommon in the mountain west as one might think. Contrary to popular opinion, the data also reveals that Kansas is not the area with the highest density of tornado outbreaks. Do you know what state has the highest density? See below.
Selecting the tornadoes by month shows the seasonal ebb and flow of the outbreak of tornadoes, starting from coastal areas near the Gulf of Mexico in January and increasing to a spatial maximum in July of each year. The numeric maximum occurs in April, three months earlier than the spatial maximum. During which six hour period do you think the most tornadoes touch down—between midnight and 6:00am, 6:00am to Noon, Noon to 6:00pm, or 6:00pm to midnight? Examining the historical data reveals that the tornado causing the most injuries (1,740) occurred in northern Texas in 1979 and the one causing the most fatalities (116) occurred in northeast Michigan in 1953. The lesson also invites you to discover in which elevation range tornadoes are most common, and the difference between tornado touchdowns and tornado tracks.
The third lesson invites students to download and analyze a single day of tornadoes. Using data from the NOAA Storm Prediction Center, the lesson begins with an analysis of 22 April 2011, the day of the tornado that caused damage at the St Louis airport. Analysis reveals that the airport tornado was only one point along a line of tornadoes that day in that region. Wind and hail for that day are also analyzed, including the determination of the mean center and standard deviational ellipse for all storm types. The lesson concludes with the students’ selecting a different day, downloading the CSV files from NOAA, and mapping and comparing them to 22 April’s storms.
-Joseph Kerski, Education ManagerAnswer: According to this dataset, tornado density is highest in sections of Oklahoma.