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The snow is gone, the temperature is warming, and the trees are preparing to bloom. With spring comes the beginning of one of the most dramatic weather seasons Mother Nature can produce: tornado season.
A tornado is defined by “Meteorology Today” author C. Donald Ahrens as a “rapidly rotating column of air that blows around a small area of intense pressure with a circulation that reaches the ground.” Every tornado has its own sound, color, and shape.
Principia College is located on bluffs, so the chance of a tornado forming on campus is slim. But right across the river is flat farmland, the perfect spot for funnel clouds to form. With proper visibility, the bluffs are front row seats for tornado watching, though this is a dangerous spectator sport.
Tornadoes have been reported in every state, including Alaska and Hawaii. But the Midwest is the most susceptible because of the atmospheric setting for thunderstorm development. Springtime caters to perfect thunderstorm conditions. With a layer of warm, humid air near the surface and a drier air mass above comes an unstable atmosphere, and thus the perfect atmosphere for the forming of storms.
In other words, when Gulf of Mexico air meets Canadian air, instability occurs. Add some strong vertical wind shear, and there’s a twister. Wind shear refers to a change in wind speed or direction with height in the atmosphere. For example, wind at one altitude is blowing at 25 miles per hour while the wind below is only blowing at five miles per hour, causing rotation.
Ahrens states that major twisters usually form in a series of stages: dust-whirl, organizing, mature, shrinking and decay. The dust-whirl stage is fairly self-explanatory. Dust begins swirling up from the ground and a funnel starts rotating downward from the storm cloud. In the organizing stage, the intensity increases, and the funnel extends closer to the surface. During the mature stage, the funnel reaches its greatest width and strongest winds. Following this, the tornado might begin to curve and weaken until it completely dissipates.
A tornado’s strength is measured on the Enhanced Fujita (EF) scale, named after severe storms researcher Ted Fujita (1920-1998). EF0 tornadoes have winds from 65 to 85 miles per hour, whereas EF5 tornadoes clock in winds greater than 200 miles per hour.
While tornadoes are beautiful, they aren’t meant to be experienced from within. When seeking shelter, it’s important to be on the lowest level and in the most interior room. Don’t open any windows because the tornado center has a lower pressure than the surrounding air.
If driving during a tornado-producing thunderstorm, you must drive faster than 70 miles per hour to outrun it. If you’re just walking in a field, your only hope to avoid a tornado is to find a ditch or a ravine and lie flat in it until the tornado passes.
The difference between a tornado watch and a tornado warning is that a watch is issued when the conditions could lead to tornado development, whereas a warning is issued when a tornado has been spotted. Either way, it’s important to take any warning seriously, even when in a concrete Maybeck house on top of the Illinois bluffs.