The Joplin Tornado of May 22, 2011

There’s more than enough meteorology to go around when it comes to looking at the deadly Joplin tornado of May 22, 2011. While spring is tornado season, Joplin is just the latest larger community this year to suffer at the hands of these capricious storms. But, today, I’m going to wear my mathematics hat and look more at the numbers involved in the storm.

According to the latest figures reported by the National Weather Service (NWS), the death toll from this EF-5, wind speeds above 200 mph, tornado has risen to 139, with an estimated 900 injured. This makes the Joplin tornado the deadliest single tornado since modern recordkeeping began in 1950; it has surpassed the June 8, 1953, Flint, MI tornado that claimed 116 lives. It is also now 8th among the deadliest tornadoes in U.S. history (a period spanning some 300 years).

It would have been even worse without Doppler radar information (Fig. 1) that allowed NWS forecasters as much as 24 minutes of warning time for local residents. Years ago, average lead times for tornado warnings were negative; in short, people didn’t know about the coming storm formally until AFTER it had already struck!

That’s one reason (of many) that the deadliest tornado on record in the U.S. occurred on March 18, 1925. This “Tri-State Tornado” (MO, IL, IN), with 695 fatalities and a 291-mile path, was rated F5 based on an historic assessment. Some, however, question whether this tornado was a single storm or a family of tornadoes spawned by a large super-cell thunderstorm. This storm occurred before current technology, storm spotters and damage survey techniques. It also occurred before rapid warning distribution capabilities.

The US annual tornado death toll through May 24, 2011 is also the highest since 1950 and 2011 is already ranked 7th among the deadliest tornado years in U.S. history.

The spate of deadly and destructive tornadoes this year, along with an incredible number of severe thunderstorms (large hail and high winds), has even prompted some to suggest that this is testimony to “global warming.” Some are now showcasing how unusual this year is compared to the past 60 years. Yet, this is the worst year since the 1974 SuperOutbreak of tornadoes occurred. If events of the past 40 to 60 years favor more storms due to global warming, where have the outbreaks been since 1974? Others are even suggesting that the urban heat island is creating more urban storms.

These claims, against a very short historical record, are folly, in my opinion. They are tantamount to what was claimed after the active hurricane years 2004 and 2005. What happened to “global warming” since those event-filled years? And a scientific analysis by Chris Landsea of the National Hurricane Center indicated that there was no discernible link between hurricanes and climate change.

As for urban tornado activity, well, there are a lot of cities that still lack a direct hit in recent years (thank goodness).

Rather, we should be looking at the real factors contributing to this year’s tornado onslaught ‘” a very active, southward-displaced jet stream, interacting with the spring return of Gulf of Mexico moisture. And even with these factors in place, the death toll and destruction would have been very different if some key storms had occurred only few miles distant from where they actually occurred. Had the Joplin twister struck the more sparsely populated countryside nearby (Fig. 2) rather than the city of Joplin, there would likely be no news story!’

NOAA has begun to look at the potential climate impacts on at least one recent tornado outbreak (late April 2011). Their results suggest that climate change is not at work.

All this leads me to consider some of the more salient mathematical factors of the storm. Perhaps the most significant numbers from this storm involve the area affected. Many aerial and ground-based mages make it appear that the storm affected the entire landscape. But, images can be deceiving (Fig. 3)!

If one assumes that the width of the circular storm remained at three-fourths of a mile throughout its roughly 6-mile (Fig. 2) trek through Joplin (and that the damage area is confined to its path), we can compute the approximate area affected.

Instantaneously, the storm’s area would be Pi (3.14) multiplied by the radius squared. With a diameter of three-fourths of a mile, the radius would be a scant three-eighths of a mile. Thus, the instantaneous area would be about 0.44 square miles (Fig. 4).

Multiply a three-fourth mile wide by a six-mile long extreme damage track and the area affected is just 4.5 square miles. Note that the most intense damage swath (Fig. 2) is even smaller.

Not surprisingly, it isn’t uncommon to see whole streets leveled, while a few city blocks away, homes or trees are untouched or have received only minor damage. The best way to view this is to check out the Joplin, MO Tornado imagery viewer. Simply click on any image square (high resolution is best) and then zoom in on higher resolution view. It’s impressive, to say the least! But, even with massive, unbelievable destruction, the whole city of Joplin was not destroyed! Compare this to the smaller community of Greensburg, KS that was almost completely obliterated by another massive tornado on May 4, 2007.

In fact, the total affected area of tornadic winds in Joplin is miniscule when matched to the area of hurricane force winds surrounding the eye of a “small” hurricane (Fig. 5). Allowing a 20-mile wide ring of high winds surrounding a 20-mile radius eye yields an instantaneous area of winds of about 3,800 square miles. If these winds travel inland for 50 miles, for example, then the affected area jumps to more than 150,000 square miles.

For years, meteorologists and others have noted the size differences between these two monster wind events. But comparing actual affected areas is eye-opening. The tornado is some 4 to 5 orders of magnitude (powers of 10) smaller than its hurricane cousin.

The final comparison involves time. Tornadoes, like Joplin, do their work in minutes. Hurricanes affect an area for several hours, while the storm itself can last for several weeks or more.

© H. Michael Mogil, 2011