11.3: Tornadoes

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Tornado Occurrence

Several of the severe weather reports mapped on May 28, 2019, were triangles, which indicate tornadoes. A tornado is a narrow, violently rotating column of air that extends from a thunderstorm to the ground. They are among the most violent phenomena of all atmospheric storms we experience. They pose a major threat when severe weather is present, and therefore, meteorologists need to track their location and intensity to warn people who may be in their path. It’s also important to analyze tornadoes post-event so that we can learn more about them. Figure $\PageIndex{1}$ shows tornado occurrences in 2019 compared to the average.

Based on the average daily tornado occurrences in Figure $\PageIndex{1}$: the time of year, on average, with the largest number of tornadoes is:
1. Jan-Mar
2. Apr-Jun
3. Jul-Sep
4. Oct-Dec

This is called Tornado Season, when tornadoes are most common in the continental U.S. The 2019 Eastern Kansas outbreak in Figure 11.2.3 is included and noticeable in Figure $\PageIndex{1}$.

The day with the most number of tornadoes is approximately ____. Hint: Tallest red bar.
1. Feb 22nd
2. Oct 31st
3. May 28th
4. Dec 15th

The strongest storm during this outbreak developed a tornado south of Clinton Lake in southwestern Douglas County, KS (NWS Topeka). It continued through southeastern Lawrence, KS (NWS Topeka) before crossing into Leavenworth County, KS, moving through the town of Linwood, KS, and the area west of Bonner Springs, KS. You can read more about this tornado outbreak on the National Weather Service report.

Tornado Alley is a region in the Central United States where most tornadoes occur in the US. It includes parts of Texas, Oklahoma, Kansas, Nebraska, Missouri, and Iowa. However, that doesn't mean tornadoes do not occur outside this region. Figure $\PageIndex{2}$ is the map of storm reports for the 2018 Halloween Outbreak.

Severe weather reports across continental US. Details in caption. — Figure $\PageIndex{2}$: Map of Severe Weather Reports for October 31, 2018. (Public Domain; Storm Reports via NOAA/SPC) Alternative description of image.

The majority of tornado reports (in red) happened in which of the following states?
1. Texas
2. Louisiana/Mississippi
3. Kentucky/Alabama

The most intense tornado of the day occurred near Fishville, in Central Louisiana. Information on this tornado can be found on the NOAA website.

The Enhanced Fujita Scale

What makes certain tornadoes more intense compared to others? And how do we know that the Fishville tornado was the most intense among the Central Louisiana Halloween outbreak? In 1971, Ted Fujita, a Japanese-American Meteorologist who studied severe weather at the University of Chicago, collaborated with Allen Pearson, the head of the National Severe Storms Forecast Center (SPC), to create the Fujita Scale to measure the intensity of tornadoes. In 2007, the Fujita Scale was replaced by the Enhanced Fujita Scale, which is more accurate and is currently used to rank tornadoes in the United States. Because it is difficult and, not to mention, extremely dangerous to try to measure the rotational wind speeds inside an active tornado, the Enhanced Fujita Scale ranks the intensity of a tornado based on the amount of damage caused. The damage, combined with previous research, is then used to determine the maximum rotational wind speeds of the tornado. Table $\PageIndex{1}$ below shows the Enhanced Fujita Scale and the six categories used to rank tornado intensity.

Table $\PageIndex{1}$: The Enhanced Fujita Scale for ranking tornadoes.
Enhanced Fujita Scale	Wind speed
EF-0	65-85 mph
EF-1	86-110 mph
EF-2	111-135 mph
EF-3	136-165 mph
EF-4	166-200 mph
EF-5	> 200 mph

The Fishville Tornado lasted 8 minutes, traveled 7.21 miles, and was categorized as an EF-2 tornado.

This would give it a ground speed of ________ mph. Hint: mph = length in miles/(time in minutes*60)
1. 45
2. 37
3. 7
4. 54
Based on the storm's rating on the EF scale, the storm likely had winds between:
1. 86 - 110 mph
2. 111-135 mph
3. 136 - 165 mph
4. 166 - 200 mph

The Fishville tornado resulted in no fatalities, two injuries, and about $200,000 in property damage. While this is just one example of a less-dramatic tornado, other tornado outbreaks were responsible for a significant number of deaths and destruction. Let's examine the devastation caused by the Joplin Tornado. It occurred on 22 May 2011, near Joplin, Missouri, lasted 20 minutes, and traveled 8.8 miles. This would give it a ground speed of 26.4 mph, which is slower than the Fishville tornado, but the Joplin tornado was categorized as an EF-5.

Based on the Joplin tornado's rating on the EF scale, the tornado likely had winds around:
1. 111-135 mph
2. 136 - 165 mph
3. 166 - 200 mph
4. > 200 mph

The storm events database recorded that the Joplin tornado resulted in the death of 158 people, 1150 injuries, and nearly $2.8 billion in property damage. This suggests that it is the rotational wind speed, rather than the tornado's straight-line ground speed, that causes most of the death and destruction during a tornado event.

Additional Reading

During the investigation, we explored Fishville tornado and some details of the Joplin tornado. You can explore detailed occurrence and damage reports from other tornadoes, outbreaks, and more information on the Joplin tornado using the following links:

El Reno tornado of 2013 - An EF3 tornado in Oklahoma.
2011 Alabama outbreak - An outbreak of multiple EF4 and EF5 tornadoes.
2011 Joplin tornado - More details on the Joplin tornado

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