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Toward Developing A Seasonal Outlook for the Occurrence of Major U.S. Tornado Outbreaks

The record-breaking U.S. tornado outbreak in the spring of 2011 prompts the need to identify and understand long-term climate signals that may provide seasonal predictability for intense tornado outbreaks. Currently, seasonal forecast skill for intense U.S. tornado outbreaks, such as occurred in 2011, has not been demonstrated. A recent study by Lee et al. [2011] used both observations and modeling experiments to find that a positive phase of the Trans-Niño (TNI), characterized by cooling in the central tropical Pacific and warming in eastern tropical Pacific, is associated with large-scale processes that may contribute to major tornado outbreaks over the U.S. In particular, they found that seven of the ten most active tornado years during 1950 – 2010, including the top three, are characterized by a strongly positive phase of the TNI, suggesting that if we can predict the TNI, we may be able to issue a seasonal warning (or outlook) for extreme tornado outbreaks over the U.S.

The main goals of this proposal are (1) to refine the potential predictive skill provided by the TNI, (2) to explore other long-term climate signals that may provide additional predictability in seasonal and longer time scales, and (3) to evaluate and potentially improve seasonal forecast skill for intense U.S. tornado outbreaks in the NCEP Climate Forecast System version 2 (CFSv2). With these three goals in mind, our work will be comprised of five tasks: (task-1) reanalyzing the severe weather database (SWD); (task-2) establishing meteorological indices for estimating the occurrence of tornadoes; (task-3) exploring long-term climate signals that may provide predictability of U.S. tornado activity; (task-4) analyzing the CFSv2 reforecasts; and (task-5) exploring the potential of an experimental hybrid dynamical-statistical seasonal forecasting system. Completing task-1 and -2 will result in a bias-corrected SWD and reanalysis based proxy tornado datasets, which will be essential for studying the tornado-climate linkage and thus useful for the wider climate and tornado research community. Completing task-3 will identify long-term climate signals that may provide predictability of U.S. tornado activity. Completing task-4 and -5 may potentially result in an experimental hybrid seasonal forecast system for U.S. tornado activity. If the experimental forecast system is shown to provide skillful seasonal predictability of U.S. tornado activity, it will be used to develop a seasonal tornado outlook at NOAA CPC.

The proposed work contributes directly to a high-priority topic for NOAA FY2012 MAPP funding Priority Area-1 Advance Intra-seasonal to Decadal Climate Prediction: “(i) Achieve an objective comparative evaluation of climate prediction skill from dynamical, statistical, and hybrid or consolidated systems to assess optimal prediction methodologies for specific applications.” This proposed work will be conducted under the auspices of the Cooperative Institute of Marine and Atmospheric Science program at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and addresses CIMAS Theme: (Climate Research and Impacts). This work is relevant to the NOAA goals: (Weather-Ready Nation: Society is prepared for and responds to weather-related events, and Climate Adaptation and Mitigation: An informed society anticipating and responding to climate and its impacts) in support of NOAA’s Strategic Plan.

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