Curious Dragonfly Monthly Science Newsletter

Tornadoes! We've all seen them. Whether we were safely in the confines of our house, seeing them on television, or confronted with them in our own backyard, tornadoes affect a major portion of the United States each year.

In recent years, tornadoes have claimed hundreds of thousands of lives, and have devastated entire communities. The Nat- ional Weather Service documents about 1000 tornadoes every year in the United States. Additionally, there are potentially

over 1000 more twisters that are undocu-mented. This is often because they are either too weak to be recognized, or have touched down in remote areas. Only a small portion of tornadoes that touch down annually are classified as violent.

THE EYE OF THE STORM

What is the strongest tornado you've ever experienced?

The intensity of a tornado is ranked by the Fujita Scale (F-Scale) or Fujita-Pearson Scale (FPP-Scale). The scale is based primarily on the damage tornadoes inflict on man-made structures and vegetation. The F-Scale of a twister is usually judged by meterologists and engineers after they have surveyed the damage.

The scale was first introduced in 1971 by Tetsuya Fujita from the University of Chicago. But how is a twister ranked by the F-Scale? In 2007, the Enhanced Fujita Scale was introduced.

THE FUJITA SCALE EXPLAINEDWhat does the F-Scale ranking of a tornado mean? The Fujita Scale is very subjective, and varies by the experience of the surveyor and meteorologist determining its ranking. The size of a tornado does not necessarily indicate its strength. Large tornadoes may be weak, while small twisters can often be violent.

A majority of annual tornadoes fall within the F0 to F1 range on the scale.

In 2012, a study was conducted to determine the ranking of documented tornadoes from 1950-2012. A similar study determined that nearly 70% of tornado-related deaths occur when a twister has been classified as an F4 or F5. This number decreased sharply over the years studied, as forecasting and awareness programs were intro-duced.

Pie chart of F-Scale study.

Tornadoes generally form where warm air is trapped underneath a layer of cold, dry air. When the warm bottom layer gets pushed up from either an influx of cold air or by heating near the ground, the instability is upset.

As the moist air rises it also cools and forms clouds and thunder- storms. If the conditions are right, the rising air will begin to spin

around what is called a central funnel. Occasionally, these clouds will reach a speed of up to 250 mph (402km). This rotating updraft is known as a 'meso-cyclone.' In the Northern Hemisphere, the rotation is almost always counter-clockwise. This funnel is not technically a tornado until it touches the ground.

A diagram of Tornado Alley.

HOW DOES A TORNADO FORM?

Though tornadoes can strike at any time, they are most prevalent in the afternoon. They can also occur almost anywhere in the world, but the United States remains the country with the highest frequency of tornadoes.

There is a flat stretch of land in the heart of the country that has earned the nickname Tornado Alley. This region - from west Texas to North Dakota - is ideal for twisters, since it is where dry polar air from Canada meets tropical air from Mexico.

While tornado season runs from early spring to mid-summer, tornadoes can occur at any time of year. May and June are typically the two months with the highest average of tornadoes.

The state with the highest average of twisters (125) is Texas.

LIFE IN TORNADO ALLEY

Infographic of tornado formation.

THE "SUPER OUTBREAK"Tornadoes are unpredictable, but few storm systems have ever been as volatile as the one that struck on April 3, 1974. Over a stretch of twodays, 147 tornadoes touched downin 13 different states, killing 308 people. The 'Super Outbreak' wasthe most violent system ever recorded, with 30 F4-F5 categorytornadoes confirmed. Statesaffected included: Illinois, Indiana,Michigan, Ohio (see right), Ken-tucky, Tennessee, Alabama,Mississippi, Georgia, North Carolina, Virginia, West Virginia, and New York. The Candaian province of Ontario was also affected.

The entire outbreak caused over $600 million (in 1974 USD) in damage. At one point during the storm, as many as 15 separate tornadoes touched down at the same time.

A twister striking Ohio during the 'Super Outbreak'

What must it have been like to live in the affected areas of the Super Outbreak?

In 2011, the destruction of the Super Outbreak was topped as a confirmed 362 tornadoes hit 21 states. In total, 348 people were killed by not only twisters, but flash flooding, hail, and straight-line winds.

A car destroyed by the 2011 Super Outbreak.

Aerial view of the destruction in Moore, OK.

OTHER DEADLY STORMS

On May 20, 2013, a destructive F5 tornado struck Moore, Oklahoma, killing 24 and injur-ing 377 others. The deadly tornado stayed on the ground for approximately 47 minutes, and was nearly 1.3 miles (2.1km) wide.

THE HISTORY OF TORNADO DETECTIONThe first possible tornado report in United States history occured in July of 1643 in Lynn, Newbury, and Hampton, Massachusetts. The report was recorded by Governor and weather enthusiast John Wintrop, who observed a sudden gust that whipped up dust, lifted his meeting house, and kiiled a bystander with a falling tree.

In 1882, U.S. Army Signal Corps Sergeant John P. Finley was placed in charge of the investigation of tornadoes and the development of forecasting methods. In 1888, Finley published 15 rules for early detection, which identified signs that a tornado formation was likely.

Tornadoes account for 80deaths and 1500 injuries annually.

What do you think was the pivotal advancement in tornado detection?

In 1943, the Weather Bureau formed experimental tornado weather systems in Kansas and Missouri. Forecasters could make advanced weather forecasts indi-cating when severe storms were favorable, but could not accurately say when and where the severe weather may occur.

Continued advancement and research in computer technology from the 1960s to the 1990s improved severe weather and tornado forecasting. The develop-ment and deployment of Doppler radar was instrumental in the process. Doppler radar enabled the National Weather Service to modernize its operation and to serve the public with improved warnings.

Doppler radar of a 'hook echo.'

Today, weather forecasters use a combi-nation of Doppler radar, enhanced satelliteimagery, and sophisticated analysis programs to make life-saving decisions. The lead time for warnings is now an averageof 15 minutes before a tornado is reported.

In 2014, the High-Resolution Rapid Refreshsystem (HRRR) began updately forecasts inthe lower 48 states on an hourly basis, using extremely sharp resolution images based on observations from ground and satellite-based sensors, radars, and aircraft. HRRR can accurately identify roaming storm likely to produce tornadoes.

Curious Dragonfly LLCTrina Terrellwww.curiousdragonfly.com303.903.5319

ENGAGING QUESTIONS!

1. What do you think it was like to predict inclement weather in the early days of meteorology?2. Have you ever been present in the aftermath of a tornado? How could you tell its path and direction?3. Where could the science of meteorology go next?4. How have tornadoes made their way into our everyday vernacular?

BE PREPARED!What can you do to prepare yourself if tornadoes are likely in your neighborhood? Here are a few helpful hints:

1. Keep updated with local forecasts, and listen for watches and warnings in your area.

2. Know the difference between a tornado watch and a tornado warning. A 'watch' defines an area where severe weather is likely to hit within a few hours. A 'warning' means a tornado has been spotted, or radar has shown circulation in a storm that could produce tornadoes.

3. Have a family plan that can be quickly set into motion.

4. Seek shelter. Basements and storm cellars are best, but if you don't have either one, move to a bathroom, closet, or interior room away from windows.

5. If you are in a car, get out and head for sturdy shelter or a low, flat area. Do not take shelter under a bridge. This is highly dangerous.