TORNADO!

Do your drivers panic or take action?
Understanding these storms is the first step to initiating emergency procedures.

Cheri Clymer | Contributor

As school buses depart for their afternoon routes, a tornado warning is issued for your county. Several routes will be in the path of this twister. Do your drivers have enough information today to respond and protect their precious cargo from one of the deadliest forces of nature?

What exactly is a tornado?
Last month, residents and school districts in Alabama, Kansas and Missouri were reminded of what a tornado can do. A tornado appears as a clockwise-rotating, funnel-shaped cloud that can extend from a thunderstorm or mature supercell, which is the largest and most dangerous type of storm. They spin under rotating storm clouds and can have winds up to 300 mph. They could be as much as a mile wide and last for hours.

However, non-supercell tornadoes are relatively common on the high plains of eastern Colorado and western Kansas and down in Florida. Although generally smaller in size than the supercell type, they can still produce considerable damage, sometimes even more than they are credited.

Since the late 17th century, many thousands of tornadoes have been recorded. They have been observed on every continent except Antarctica; however, most of the world’s tornadoes occur in the United States. The earliest known U.S. tornado was located in Rehobeth, Mass., in August 1671.

Recorded history shows that tornadoes can occur at any time of the year. In the southern region of the United States, the prime season is March through May. Northern states experience tornado activity during late spring through early summer. The storms in March killed at least 19 people. Historically, an average of 52 people per year are killed during peak event times. Location really doesn’t matter, as tornadoes can form in any type of terrain including rivers, lakes and mountains.

In the early 1970s, a method was developed to understand and record the strength of these powerful storms. The scale was applied retroactively to U.S. tornado reports from 1950 on, but occasionally to even earlier infamous tornadoes.

The Fujita or Fujita-Pearson scale (F-Scale), is a method for rating tornado intensity based on the damage inflicted on both human-built structures and vegetation. Previously used in most areas outside of Great Britain, it has since been superseded by the more accurate Enhanced Fujita Scale in the United States. The Enhanced Fujita Scale, or EF Scale, National Weather Service (NWS) Improved Tornado Rating System is now operational. On Feb. 1, the NWS fully implemented the EF scale to rate tornadoes, replacing the original Fujita Scale. The EF scale will continue to rate tornadoes on a scale from zero to five, but ranges in wind speed will be more accurate with the improved rating scale.

Tornadoes are classified according to their intensity: weak, strong or violent. Approximately 85 percent of all tornadoes are classified as weak (EF0 1 or 2), meaning they usually cover less than 3 miles on the ground, last only a few minutes and have an average path of less than 100 feet wide. But their wind speed may be as high as 120 mph, causing casualties and substantial damage.

Strong storms (EF3-4) fall into the 13 percent category. These tornadoes have a life span of 15 to 20 minutes, with wind speeds of up to 200 miles per hour. Their path of destruction can be as wide as ¼ mile and as long as 30 miles. These storms cause considerable damage and loss of life.

The last groups of tornadoes, those classed as violent (EF5), are the most dangerous. They are rare but responsible for most of the deaths and destruction. They can be on the ground for as long as an hour, and the path they cut can be over a mile wide and 100 miles long.

One of the most powerful in recent history was the storm on May 3, 1999, in Oklahoma City. Sixty-one tornadoes touched down that day causing 790 injuries, 44 deaths and $1.3 billion in damages. Sixteen counties were declared disaster areas.

Clymer is a certified pupil transportation safety trainer for the Thompson School District in Loveland, Colo., and she is co-developer of the NAPT School Bus Emergency Manual. Next month, she will give best practices for ensuring school bus operations and employees are prepared for tornadoes.