Tornado Warning

Foreword

Foreword

“There are some things that you never forget. You never forget the feeling. It will always be there and it's so hard to describe.” —Kayla McMinn

On May 22, 2011, a supercell of four different tornadoes struck Joplin, Missouri. One hundred and fifty-nine people died as a direct result, and over eleven hundred were injured. More than 7,600 homes and dwellings were destroyed. All of this happened in an area of six square miles as the tornado moved through the city from the south to the east.

Tornadoes occur all over the world, but the majority of them occur in the United States, east of the Rocky Mountains. About 800 are reported every year. A tornado is a "violently rotating column of air" that drops to the ground from a thunderstorm.

The most violent of tornadoes have wind speeds of 250 mph or more. They can stretch up to one mile wide and live for as long as fifty miles. The Joplin tornado had wind speeds of 200 miles per hour, was one mile wide in places, and covered more than twenty-two miles.

Tornadoes stem from thunderstorms, which develop when cold (generally dry) air moves into warm, moist air. Large hail and strong winds are precursors for a tornado.

Sometimes it is not the temperature difference that forms a thunderstorm, but the moisture difference. The warm, dry air moving into the warm, moist air is a common condition in the Central Plain region, such as Kansas and Missouri.

The changing winds and air direction of a thunderstorm creates a horizontal wall of air. This air often spins, or rotates. A funnel cloud forms when the updraft from a thunderstorm tilts this wall vertical rather than horizontal. The rotating continues, and most tornadoes are formed inside this vertical wall.

Tornadoes can be difficult to see when they first form. Often it is the debris and dust that is visible in the twisting vortex, rather than the cloud itself. When one tornado is created, the conditions are right for another to form as well.

Most tornadoes are weak and live less than ten minutes, having wind speeds of only about 100 mph. Only two percent are strong and violent; yet these twisters are responsible for seventy percent of deaths caused by tornadoes.

Tornadoes can occur anywhere, even mountains and lakes, at any time of year.

The Fujita Scale

The Fujita Scale (hence the F in the F-scale rating) was developed by Dr. Theodore Fujita. He envisioned a chart that classified tornadoes by area and intensity. Originally, his categories were:

F0 (Gale)

F1 (Weak)

F2 (Strong)

F3 (Severe)

F4 (Devastating)

F5 (Incredible)1

Eventually, these ratings became more scientific, resulting in the following chart:

It is interesting to note that the judgment is not based on measured wind speed, but on the damage caused by the wind. There are twenty-eight damage indicators, starting with the destruction of a small barn at level 1 to the destruction of a softwood tree at level 28, though they aren't necessarily in order of severity. Each level also has a chart to differentiate between the degrees of damage (DOD).2 Thus, the F-scale is not so much a rating of wind speed as it is of the destructive force of the tornado. So level 4 at DOD 12 (total destruction of a mobile home), would have wind speeds of about 134 miles per hour and would be considered an F2. Level 19 at DOD 10 (significant damage to a ten-story building, estimates wind speeds of 228 miles per hour. This tornado would be an F4. The Joplin Tornado was an F5.

The tornado scale is now called the derived Enhanced F-scale. Hence the tornadoes are measured as EF1, EF2, EF3, EF4, and EF5.

The Joplin Tornado

The four tornadoes were created from two supercell storms. One tornado was an E5, two were rated E4, and one was an E3. An E5 hadn't hit Joplin or the surrounding area since 1925, nearly a century earlier. This tornado was the deadliest to strike in the United States in the modern era. It traveled almost fourteen miles through the Joplin city boundaries. It began at approximately 5:34 p.m. and ended around 6:12 p.m., lasting about thirty-six minutes. Almost 16,000 people were in the direct path of the tornado.

Severe weather and flooding continued in the area for the next three days, all of it a result of the supercell that spawned the E5.

One hundred and fifty-nine people died as a direct result of the tornado, and over eleven hundred were injured. More than 7,600 houses and dwellings were destroyed. All of this happened in an area of six square miles as the tornado moved through the city from the south to the east.

Contributing Weather Conditions

"A series of complex meteorological events and interactions took place during the afternoon hours of May 22 that eventually resulted in the devastating EF5 tornado."3 These events were:

1) A 500 millibar jet core at around 55 and 65 knots (or about 63 and 74 miles per hour) remained mostly stationary over the region. The typical jet stream is about 300 millibars strong.

2) The winds over the Joplin area increased by about 50 knots (or about 60 miles per hour).

3) Winds that had been heading south changed directions and increased by about 35 knots (or 40 miles per hour).

4) A weak surface low (or area of low pressure) formed across the most southeast part of Kansas.

5) A dry patch followed on the heels of the surface low and spread out farther than expected across southern Kansas and northern Oklahoma.

6) A slow-moving cold front spread to the north and east of the low.4

These six factors then led to three more problems which created a triangular effect: Winds increased to 60 knots. Moisture pooled in the southeastern area of Missouri. Weather temperature all day Sunday was in the 80s, hotter than what had been forecast, which increased the Convective Available Potential Energy (CAPE).

Hodographs, or diagrams that give a visual representation of a body of air, revealed the classic sickle shape that indicates an increase in tornado potential. The supercell showed a definite eastward movement.

A series of storm mergers occurred half an hour before the Joplin tornado developed. At first, the supercells moved in a northeast direction. But radar operators noted that at least one of the cells was making a gradual right turn. This observation would prove critical for the advanced warning that Joplin received.

Two more storm cells formed and interacted with the (already mentioned) supercell. It developed a mesocyclone that prompted the first warning in Jasper County. A third storm developed and interacted with the ones in the north. This last storm developed quickly and became the dominant cell. It was this cell that prompted the first Tornado Warning for Joplin at 5:17 p.m.

At this point the radar operator made a judgment call: he opted to send out the warning using the WarnGen system instead of the Pathcast. The difference was that with the WarnGen system, the warning went out to all cities and towns that could possibly be in the vicinity of the tornado, as opposed to the Pathcast, which would calculate the direct path of the tornado and create the warning for those in the direct trajectory. Since the tornado proved to be unpredictable, more than once changing directions and speeds, his decision likely saved numerous lives.

Two more storm mergers occurred after the Joplin warning was issued. The first merger increased the wind speed to 100 knots. The second merger brought the water, creating the rain-wrapped vortex of the Joplin tornado. This violent storm was now in the Joplin city limits.

The tornado developed very rapidly, with intensity increasing in seconds. The reasons for this are unclear, though research is being conducted.

Timeline

Weather officials watched the storm develop throughout the weekend. The first indication of a storm began at 2:30 a.m. on Friday. At that time, the probability for a super storm was a “slight risk.” A few hours later, at 5:30 a.m., that had changed to a potential for severe or strong Sunday storms.

That expectation held steady over Friday and Saturday. By Sunday morning near 1:00 a.m., weather officials discussed the 10% probability of severe and isolated tornadoes in the area. By 5:12 a.m., the risk upgraded to "limited."

By 10:00 a.m. on Sunday, the possibility of supercells was mentioned. The risk of tornadoes was expected to go up as the evening progressed. At 11:31 a.m., the risk went from "limited" to "elevated," based on the weather patterns that meteorologists were noting for the area.

Storms began forming between 2:00 and 3:00 p.m. that afternoon in Kansas and Oklahoma.

A little after 1:00 p.m. on Sunday, May 22, the Storm Prediction Center (SPC) noted the convective pattern, or convective available potential energy (CAPE). The development of cumulus clouds along the dry patch indicated an eruption of intense supercells. The instability of the atmosphere created the right mixture for a tornado to form. SPC scheduled a conference call to discuss the possibility of a tornado, which was higher than previously expected, but still not probable. The biggest expected threat was large hail. Even so, the possibility of a tornado required a Tornado Watch, which was issued at 1:30 p.m.

The first thunderstorms of the day formed in front of the dry line of Kansas and Oklahoma by 3:00 p.m. A warm jet stream blew into the area, auditing the formation of thunderstorms. The storms quickly developed the characteristics of a supercell: low and mid-level moisture with a lot of precipitation, as much as one and a half inches. Wind fields were only slightly higher than the thunderstorms. The storms interacted and merged together in the manner customary of a supercell. Hail ranging from golf ball-sized to baseball-sized pummeled the area. The storm quickly became severe, prompting Severe Thunderstorm Warnings from the Weather Forecast Office (WFO) in Springfield.

"As severe storms moved east, forecasters became increasingly concerned about their tornado potential and issued the first Tornado Warnings of the day at 4:25 p.m. and 4:51 p.m. for portions of Cherokee and Crawford Counties in southeast Kansas, west of Joplin."5 This initiated a conversation with Jasper County about the supercell in southeast Kansas. At 5:09 p.m., the Tornado Warning for Jasper County was issued.

At this point things quickly picked up speed. The Joplin weather tower was notified at 5:15 p.m. The warning was valid until 6 p.m., with an additional notice that there might be more than one tornado cell moving across Jasper County.

People in Joplin began calling in reports of hail at 5:34 p.m. At the same time, a tornado moving toward Joplin at twenty-five miles per hour from Galena, Kansas, was spotted. "The first indication of a confirmed tornado was issued via another Severe Weather Statement at 5:39 p.m. CDT that stated, 'At 5:34 p.m. CDT...trained weather spotters reported a tornado near Galena' and that 'This storm is moving into the city of Joplin.'"6 The tornado first touched down at the intersection of JJ Highway and Newman Road, just outside Joplin. It intensified and gain E5 status by the time it entered the Webb City limits.

At 5:41 p.m., the tornado entered Joplin.

LSR (Local Storm Report) immediately communicated numerous power flashes, presumably caused by the tornado as it blew out transformers and tore up electrical lines.

By 5:46 p.m., the tornado had already inflicted great damage. The vortex maintained E5 status for most of the fourteen miles it traveled through Joplin. Reports came in of collapsed housing structures and damage to Range Line, 22nd, 13th, and Blackcat Road. The reports kept coming, and the details were grim. By 6:02 p.m., LSR reported that a tornado had blown through I-44 between markers 10 and 12, knocking more than twenty semi-trailer trucks and cars off the interstate. "All interstate signs" were "gone and damaged."7 The force of wind required to knock semi trucks off the highway and twist and destroy pieces of sheet metal is nearly unfathomable.

As the tornado continued moving east, Severe Weather Service (SVS) issued a statement that "this storm has a history of producing a large damaging tornado in Joplin Missouri."8

The storm pushed its way through Joplin and continued into Diamond, Missouri, where it dropped to an E1 status. By the time the tornado lifted outside of Duenweg, Missouri, it had traveled twenty-two miles.

The damage was done. A storm that took days to develop eradicated entire sections of Joplin within minutes.

The National Weather Service jumped into action. Six members were on staff during the tornado, with a seventh arriving midway through the event. As the damage reports came in, staff notified management and requested backup. Management arrived and quickly began the task of organizing rescue and cleanup operations.

Public Response to the Tornado

The tornado did not catch the city of Joplin by surprise. "Despite being focused mainly on very large hail as the primary severe weather threat prior to thunderstorm development, warning forecasters did an outstanding job of recognizing the tornado potential of the storm that moved through Joplin and issued an accurate Tornado Warning with sufficient lead time for people to take life-saving action."9 Twenty-four minutes before the tornado touched down in Joplin, news officials started sounding the sirens. Sixty-four Severe Weather Warnings and thirty-six Tornado and Severe Thunderstorm Warnings were issued.

The death toll seemed especially high, considering the advanced notice. This could have been because "the tornado developed rapidly on the southwestern outskirts of a densely populated area and had moved through much of the city before the size and violence of the tornado was apparent to warning forecasters. Thus, they did not issue a Severe Weather Statement with a Tornado Emergency headline for Joplin proper."10

The warnings were issues via television and radio, government and weather websites, two separate tornado sirens, text messages, posts on f*******:, and transmissions over the weather radio. Additional unofficial warnings came from direct observation of the weather, and from family, friends, and neighbors who commented on the warnings.

In spite of these many warnings and precautions, some people were still caught unaware, resulting in an unfortunate number of deaths. The Joplin tornado was the first to have caused over 100 deaths since the 1953 tornado in Flint, Michigan. Reasons for this could be:

1) The tornado was almost a mile wide, with winds of 200 miles per hour.

2) The tornado didn't always move in one direction, and often changed speeds.

The Weather Forecast Office scanned the tornado every five minutes to ascertain the size of the event. Because of the speed of the tornado, however, it had often completely altered course by the time a next scan occurred, leaving weather operators scrambling to project its path. The WFO is considering ways to increase the scan to one-minute intervals.

3) Insufficient available shelter.

Most people who took shelter did so in appropriate places, or the best available to them, such as bathrooms, interior closets, basements, and storms shelters. Unfortunately, belowground shelters weren't common, and many people had no safe place to go. Early assessments indicated that more than 50% of fatalities occurred in the home. While an estimated 30% of deaths occurred at local businesses, the actions of employees saved the lives of many patrons.

4) A varied response to the warning.

While many people heard the sirens or were aware of the Tornado Warnings, many didn't believe them. Some didn't take any action at all. Those who did often had no place to go, and sought shelter in hallways and bathrooms. Many people chose to wait and see, relying on their own ability to "sense" danger before seeking cover. This is evident even in some of the interviews you'll read in this book. For some people, it took as many as nine different warnings before they took the threat seriously.

Many people familiar with the spring weather in Southwest Missouri noted that tornado watches and warnings are common. However, these same people didn't feel that Joplin was ever affected by such weather patterns. This is called "optimism bias," where people think the risk for others is higher than for themselves. Somehow, they thought Joplin would always be passed over.

The policy in Joplin is to sound the sirens when a tornado is moving toward the city, or thunderstorm winds are expected to reach seventy-five miles per hour or higher. Once activated, the sirens turn on for three minutes, then turn off. Because there is no way to know which threat the sirens are indicating, many people didn't take them seriously. Also, because the sirens shut off after three minutes, some residents assumed that meant the threat was over.

The sirens had lost credibility in Joplin as being a warning of imminent danger. Because of this, WFO suggests creating a different siren that is only used in immediate emergencies. It would need to be used infrequently, thus dispelling the problem of false alarms and complacency. Joplin's policy is usually to sound one siren for an event. Therefore, when the second siren went off, many residents noted that this was unusual. It helped many to realize the threat was real, and not just another warning.

Some people relied on their own ability to recognize a tornado approach; however, this proved difficult with the Joplin tornado, as it was wrapped in rain. Therefore it looked like a dark cloud rather than a funnel cloud. Many people didn't realize it was a tornado until it was at their doorstep, quite literally, as evidenced in the story of Kayla McMinn.

The WFO recognizes they could have given a better warning. They stated that, "the Severe Weather Statement issued at 5:42 p.m. CDT and Tornado Warning issued at 5:48 p.m. CDT should have been more strongly worded and portrayed a greater sense of urgency." Instead, the statement and warning were worded very much like previous warnings and statements issued that day.

As the tornado moved through Joplin, radio and TV coverage switched to live commentators, and the urgings to "take cover now," along with reports of the devastation already created, prompted most to seek shelter. This sort of warning had a feeling of immediacy and an urgency that forced people to act without delay.