Last year went down in the books as one of the worst U.S. tornado years on record. Can we say anything about how many tornadoes we'll have in 2012?
Forecasting companies AccuWeather and Telvent have issued 2012 tornado outlooks. On the academic side, Columbia University's International Research Institute (IRI) for Climate and Society has published a new technique for developing seasonal tornado forecasts.
AccuWeather predicts above-normal tornado numbers in 2012, but not as many as 2011. It says warmer than normal water in the Gulf of Mexico will provide the moist, unstable air to energize thunderstorm development and help spin up tornadoes. On the other hand, AccuWeather notes that the climate pattern called La Nina is forecast to weaken. In 2011, La Nina led to a very strong northern jet stream that fueled violent storms as it dived into the Midwest and South.
Meteorologist Jeff Johnson of Telvent thinks that even a weak La Nina will influence tornado activity. "As we head toward the spring season our expectations are that 2012 will favor above-normal tornado numbers once again, primarily due to La Nina," he said in a recent blog post.
At IRI, lead researcher Michael Tippett and colleagues have published a new tornado forecasting method that may provide about a month's lead time on expected tornado activity. Using historical data, his team identified two weather variables most associated with tornadoes -- rain and spin in the atmosphere -- and created an index that can be put into a model to make forecasts.
In tests, the model "was able to use the index to forecast monthly tornado activity with some success up to a month in advance. This success, especially notable in June, is the first evidence for the predictability of monthly tornado activity," the IRI noted in a press release.
Even if perfect outlooks about the number of tornadoes were possible, what is the value? Tornadoes are so localized that simply knowing in advance that a given month or season is going to be active may not be helpful. This same question comes up in discussions about the usefulness of seasonal hurricane outlooks, even though hurricanes affect much larger areas.
But Harold Brooks, a tornado researcher at the National Oceanic and Atmospheric Administration, thinks these outlooks might offer some utility.
"If I'm a state emergency manager, I might be really interested in knowing at the end of March that by the end of April we could have a big problem," he told IRI. "You could be better prepared with generators and supplies."