Joplin tornado report; Did “optimisim bias” kill?

The NWS released an extensive report on the devastating Joplin tornado this spring.

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Among the many findings on how people reacted (and why many may have died) is that many people in Joplin basically ignored initial warnings about the storm and failed to take protective action.

It’s a classic study on a difficult fact that you can give credible accurate severe weather warnings, and sometimes people still ignore then, even at risk of imminent death!

First the basics from the report: (My highlights in bold)

“On May 22, 2011, one of the deadliest tornadoes in United States history struck Joplin, Missouri, directly killing 159 people and injuring over 1,000. The tornado, rated EF-5 on the Enhanced Fujita Scale, with maximum winds over 200 mph, affected a significant part of a city with a population of more than 50,000 and a population density near 1,500 people per square mile. As a result, the Joplin tornado was the first single tornado in the United States to result in over 100 fatalities since the Flint, Michigan, tornado of June 8, 1953.”

The Track:

Here’s the track of the deadly Joplin EF5 tornado.

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Plenty of warning “lead time:”

From an NWS and meteorological perspective, this was a “well warned” event.

Looking at the timeline of events below you can see there was a full 25 minute lead time from the first tornado warning and the initial tornado touchdown! Sirens wailed 23 minutes before the tornado touched ground southwest of Joplin.

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“Optimism Bias:” People ignored warnings, failed to act:

So called “optimisim bias” played a role in people not taking decisive action in Joplin.

From the report:

“The vast majority of Joplin residents did not immediately take protective action upon receiving a first indication of risk (usually via the local siren system), regardless of the source of the warning. Most chose to further assess their risk by waiting for, actively seeking, and filtering additional information.

The reasons for doing so were quite varied, but largely depended on an individual’s ―worldview formed mostly by previous experience with severe weather. Most importantly, the perceived frequency of siren activation in Joplin led the majority of survey participants to become desensitized or complacent to this method of warning. This suggests that initial siren activations in Joplin (and severe weather warnings in general) have lost a degree of credibility for most residents – one of the most valued characteristics for successful risk communication.

Instead, the majority of Joplin residents did not take protective action until processing additional credible confirmation of the threat and its magnitude from a non-routine, extraordinary risk trigger. This was generally achieved in different ways, including physical observation of the tornado, seeing or hearing confirmation, and urgency of the threat on radio or television, and/or hearing a second, non-routine siren alert.

Interviews showed aspects of worldview that influenced risk perception and warning response included: previous experiences with tornadoes, apathy, familiarity with seasonal weather patterns in southwest Missouri, optimism bias, perceived frequency of siren activation in Joplin, social networks as mechanisms for warning dissemination, avid fear of tornadoes, and the number of deadly tornadoes earlier in the year.”

“Normalization” of severe weather:

The notion that storms “always seem to fade or go around” Joplin played a role that day. Sound familiar Twin Cities?

Again, from the report:

“Similarly, familiarity with seasonal weather in southwest Missouri played a major role in risk perception and warning response. Most individuals commented that severe weather in southwest Missouri during spring is common; however, tornadoes never affect Joplin or themselves personally. It was common in the interviews to hear residents refer to ―storms always blowing over and missing Joplin,‖ or that there seemed like there was a ―protective bubble‖ around Joplin, or ―there is rotation all the time, but never in Joplin.‖.

One city employee stated, ―… don’t think it can’t happen in your community, because that’s what I thought.‖ This sense in which people believe their personal risk from a hazard is less than the risk faced by others is referred to as optimism bias and can lead to diminished perceptions of threat and influence response.

In Joplin, it is community policy to sound sirens when either a tornado is reported to be moving toward Joplin or severe thunderstorm winds are expected to exceed 75 mph. These triggers may or may not be associated with an NWS warning, and the Jasper County/Joplin Emergency Manager has discretion and uses professional judgment on when to activate sirens. These types of local warning system policies are by no means unique to Joplin.”

“Warning confusion:” Too many severe weather sources?

How many sources of severe weather information is too many in this technological age? Is it really wise to buy that latest smart phone severe weather app? Or is it better to rely on one credible source of severe weather info? The reality is probably a combination, but the lesson form Joplin is clear. If a tornado warning is issued, don’t assume you have time to figure it out. Take cover FIRST, and then sift through additional sources for clarifying info.

Some examples of “risky” recations to intial (and in some cases multiple) warnings before the tornado hit from the report:

“The number of signals between first indication of severe weather and protective action markedly increased as information became conflicted or unclear. In the most extreme example, one resident’s interview indicated nine risk signals identified before taking protective action:

1. Aware that thunderstorms were probably going to happen

2. Noticed the weather changing outside

3. Heard the 1st siren while driving to restaurant (approximately 30-minute lead time)

4. Restaurant shut doors and disallowed entry

5. Drove to a 2nd restaurant where business was carrying on as usual

6. Noticed the weather changing

7. Reports came from TV and radio

8. Patron indicated tornado in Joplin

9. Management instructed protective action

In one example, a man was clearly confused by the string of warning information he received and processed from various sources.

1. Heard first sirens at 511 pm CDT (estimated 30-35 minutes before tornado hit).

2. Went to the TV and heard NWR warning from TV override that indicated tornado near airport drive 7 miles north (polygon #30) of his location.

3. Went on porch with family and had a cigar. Looked like a regular thunderstorm.

4. Heard second sirens (estimated 27 minutes later).

5. Thought something wasn’t right so went inside and turned local TV stations on.

6. Saw on TV several colored counties for tornado warnings, but regular programming was still on and thought the threat was still to the north.

7. Heard his wife yell ―basement,‖ grabbed the cat and told son to put his shoes on.

8. Tornado hit as they reached the top of the basement stairs, destroying their home.”

“Wall to wall” media coverage saved lives:

It appears we are now (rightfully so?) conditioned to respond when local media (primarily radio & TV) break into local programming with “wall to wall” coverage of severe weather.

“Finding #2d: The majority of surveyed Joplin residents did not take protective action until receiving and processing credible confirmation of the threat and its magnitude from a non-routine trigger.

While searching for additional information concerning the severe weather threat constitutes ―taking an action,‖ the actions many residents described taking were not the immediate life-saving measures desired with the issuance of a tornado warning. In most cases, these life-saving actions, or the decision to find shelter, were associated with additional extraordinary risk signals. This was generally achieved in different ways, including:

a. Physical observation of the environment (seeing the tornado approach).

While significant numbers of people actually did this, the approach was complicated by having a ―rain-wrapped‖ tornado that made the tornado more difficult to recognize until it was very close. There were numerous accounts of people running to shelter in their homes just as the tornado struck, despite significant advance warning of the risk.

b. Seeing or hearing confirmation of the threat on radio or television, seeing the large tornado on the air, or hearing on-air instructions to ―take cover now.‖

When the tornado began moving into Joplin, most local electronic media switched to ―wall-to-wall‖ coverage of the event, which included live video from tower-cams.

As coverage quickly evolved, and the magnitude of the event became clear, on-air commentators implored those in the path to take cover immediately. This kind of media coverage helped convey the seriousness and urgency of the situation, and prompted many listeners and viewers to find shelter.

c. Hearing a second, non-routine, siren alert at approximately 538 pm CDT.”

There’s a lot more to sift through in this extensive report, but the findings are an eye opening study about how and why people respond in different ways to severe weather information.


  • Tony Yarusso

    We NEED to get sirens that are capable of sounding a wider variety of alarms, and then teach people what they mean. I totally understand the reaction of people in Joplin, as right here in Ramsey County our warning sirens are exactly the same for Severe Thunderstorm Warning and Tornado Warning, which are VASTLY different in terms of severity and urgency. A warning signal is useless if I can’t tell what it’s trying to warn me OF when I hear it.

  • Jeb Rach


    The average layperson has a hard time noticing the difference in damage between a really strong straight-line wind event and a tornado.

    I’d want to be in a sturdy shelter in either case. However, one is a severe thunderstorm warning, and the other is a tornado warning.

    My understanding is that the sirens only sound in an extremely severe thunderstorm event (such as the winds are above 75 mph or extremely large hail). In either case, I’d want to be inside ASAP. Even a car wouldn’t be adequate shelter then.

  • Tony Yarusso

    Living in a neighborhood that had damage from an 80mph straight-line wind event once, you’re right that it can do quite a bit, but even that was nowhere near the severity done by tornados in places like Joplin or Hugo. Certainly the comparison is closer if you only look at small, “weak” tornados, but I’ve never seen a 200mph straight-line wind event in this part of the country. Also, when that happened, we had a lot of notice (from the weather itself, not the alert system). It takes more time for straight-line winds to get going than it does for a tornado to arrive at your location. You are correct that I’d want to be in shelter in either case, but they are still very different in HOW sturdy of a shelter I’d want to be in and how QUICKLY I’d feel I needed to get there, and that can be the difference between people being killed or not.

    As for your understanding of when sirens are used, I’d have to say on a purely anecdotal basis that it doesn’t seem quite right, as the ones in my neighborhood (Shoreview, Ramsey County) have gone off for severe thunderstorms that did not have winds of that magnitude. Still “damaging” winds, but not of that caliber.

  • Jeff

    KISS principle applies here. Sirens sound, take shelter as though it was a strong tornado headed directly for your location. Same applies for warnings received via NWS weather radio or broadcast media. Sort out the details while in shelter or after the warning has expired. It is 30 or so minutes of inconvenience that may actually save your life and those of loved ones.

    Don’t question the technology, the accuracy or the cry wolf thing. Just take shelter.