How to predict a tornado: What do we know?

Currently we can do this with as much as 15-20 minutes warning. But forecasting actual tornadoes is beyond our reach now.

Questions:

1. Ordinary people usually think that the tornadoes are really hard to predict. Is it really so difficult and what is the biggest challenge when we try to predict the strength and direction of tornadoes?

2. With regard to catastrophes as in Moore, is it anything we can learn from them talking about the forecasting tornadoes, is it possible to use data we know now to make our predictions better?

Answers:

Mary Stampone, Assistant Professor of Geography and New Hampshire State Climatologist, University of New Hampshire

1. With today’s technology, identifying the conditions that make the atmosphere favorable for tornadoes to develop (energy, wind shear with height, rotation) is not difficult. With that information, regional watches are issued hours in advance and local warnings may be issued up to an hour or more in advance of a tornado touchdown. The difficulty comes with the fact that even with the right conditions a tornado may not form within every thunderstorm cell and the size and magnitude of a tornado that may form is difficult to determine before it reaches the ground. Tornadoes are usually short-lived and are small in comparison to other weather phenomena, making the details of each tornado more difficult to forecast in advance. Once detected and spotted on the ground, the general track is not difficult to determine but given the size of a single tornado compared even to the thunderstorm cloud that produced it, an uncertainty in the tornado’s path of even 500 meters can mean the difference between complete destruction of your home or your neighbor’s. With that, a warning or emergency can be sent to a town or city 10 to 20 minutes (average warning time is 15 minutes, Moore OK had 17 minutes) before the tornado arrives but which neighborhood or building lies directly in the path is known only minutes before.

2. Storm chasers and meteorologists are constantly providing and analyzing tornado data to improve forecasts and warning times. Tornado forecasts have significantly improved over the past few decades leading to a more than doubling of the average warning time since the 1970’s. The real problem now is not necessarily with the forecasts but getting the information out to the public and the public response to those warnings. Digital communication technology and social media have improved the ability of forecasters to reach the public and public access to storm information. Appropriate public response is therefore key to saving living lives. There are two problems here. Since warnings are issued fairly regularly and many times a tornado does not form, one does form but it is small and short-lived, or one forms in a rural area without impacting many people. This gives a false sense of security leading the belief that it won’t be bad or it won’t strike me. The second problem is with large tornadoes like the one in Moore. There is no safe place above ground during an EF4 or EF5 tornado. People can survive smaller tornadoes in their bathroom or an interior closet, but not in and EF4 or EF5. Many buildings in the Moore area did not have basements and storm shelters built to withstand wind speeds up 200MPH or greater are expensive, so many people do not have them. Without a basement or a proper storm shelter, the only thing to do is get out of the way. So even as forecasts improve, preparedness and response are key components to mitigating the loss of life during a tornado.

Anthony Lupo, Department Chair and Professor Atmospheric Science, University of Missouri

1. With tornadoes, our current strategy is to forecast and recognize the large and medium scale processes that make tornado formation likely. This gives us a general area and time for the most likely tornado strikes. It is very difficult to know which thunderstorms will become tornadic, so we try to identify structures which correspond to tornado formation using RADAR. Currently we can do this with as much as 15-20 minutes warning. But forecasting actual tornadoes is beyond our reach now. Once they form, we know they move in the same direction as the thunderstorm.

2. Yes, events like Moore are strong and will provide us a wealth of information to better understand tornado formation which is not completely understood. Also, the RADAR signatures might provide additional clues as to the formation of tornadoes.

Robert Henson, Science Writer, Meteorologist, University Corporation for Atmospheric Research

1. Although there are still many questions about how tornadoes form, the main ingredients that cause tornadic thunderstorms are well understood. Often forecasters can determine several days in advance that a given region (say, the size of Slovakia) is likely to experience severe thunderstorms, perhaps with some tornadoes. And once a tornado develops, radar displays can provide very accurate warnings as to where the tornado is headed. One of the biggest challenges right now is determining a few hours in advance with some confidence exactly which areas will see tornadoes and which ones will not. This is the goal of our MPEX study.

2. The MPEX study released a number of radiosondes–balloons that carry weather instruments–into the heart of the thunderstorm that produced the Moore tornado. These will provide valuable data on the processes going on while the tornado was happening. It will also be helpful to use computer models to find out what information would have helped to predict the Moore tornado ahead of time.

Michael BrownAssociate Professor, Department of Geosciences, Mississippi State University

1. Yes individual tornadoes are difficult to predict. The conditions that create the type of storms that are associated with tornadoes are not hard to predict. We do a good job of outlining areas where storms and tornadoes are likely to form, but we are long way from knowing exactly where these types of storms will form. There are many ingredients necessary for these types of storms and many of these ingredients occur at very small scales, and we simply cant yet measure them (we don’t have the tools to measure on such fine spatial and time scales).

2. What will come out of the Moore, OK tornado, like other big devastating tornadoes, is a better public awareness. As our tools get better, forecasting these storms will get better. Right now, people need to take every warning seriously, and understand that every tornado has the potential to be deadly.

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