The Extended-Range Tornado Activity Forecast (ERTAF) Project

Vittorio A. Gensini, John Allen

Research output: Contribution to journalArticlepeer-review


AbstractLarge-scale weather patterns favorable for tornado occurrence have been understood for many decades. Yet, prediction of tornadoes, especially at extended lead periods of more than a few days, remains an arduous task, partly due to the space and time scales involved. Recent research has shown that tropical convection, sea surface temperatures, and the Earth-relative atmospheric angular momentum can induce jet stream configurations that may increase or decrease the probability of tornado frequency across the U.S. Applying this recent theoretical work in practice, on 1 March 2015, the authors began the Extended-Range Tornado Activity Forecast (ERTAF) project, with the following goals: 1) to have a maproom-style discussion of the anticipated atmospheric state in the two- to three-week lead window; 2) to predict categorical level of tornado activity in that lead window; and 3) to learn from the forecasts through experience by identifying strengths and weaknesses in the methods, as well as identifying any potential scientific knowledge gaps. Over the last 5 years, the authors have shown skill in predicting U.S. tornado activity two- to three-weeks in advance during boreal spring. Unsurprisingly, skill is shown to be greater for forecasts spanning week 2 versus week 3. This manuscript documents these forecasting efforts, provides verification statistics, and shares the challenges and lessons learned from predicting tornado activity on the subseasonal time scale. (Capsule Summary) A team of scientists have been holding virtual maproom discussions every Sunday evening during boreal spring to develop and apply techniques to forecast U.S. tornado activity 2- to 3-weeks in advance.
Original languageEnglish
Pages (from-to)E700-709
JournalBulletin of the American Meteorological Society
StatePublished - Jan 2020


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