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Katrina Grantz, Balaji Rajagopalan, Martyn Clark, and Edith Zagona

1. Introduction and background The North American monsoon system (NAMS) is the large-scale atmospheric circulation system that drives the dramatic increase in rainfall experienced in the desert southwest United States and northwestern Mexico during the summer months of July, August, and September. These summer thunderstorms typically begin in early July and last until mid-September and can account for as much as 50%–70% of the annual precipitation in the arid region ( Carleton et al. 1990

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Fuyao Wang, Zhengyu Liu, and Michael Notaro

modes have not been well studied. ENSO is considered the most prominent source of climate interannual variability, and its impact on North American climate has been recognized for decades ( Ropelewski and Halpert 1986 , 1987 ; Ting and Wang 1997 ; Zhang et al. 2011 ). In winter, past studies generally agree that, during the warm phase of ENSO, the air is warmer than normal stretching from northwestern North America to eastern Canada, colder than normal in the southern and southeastern U

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Richard E. Orville, Gary R. Huffines, William R. Burrows, and Kenneth L. Cummins

1. Introduction Lightning incidence throughout northern Mexico, the continental United States, Canada, Alaska, and nearby coastal waters is currently observed by the North American Lightning Detection Network (NALDN). This network is operated as a seamless integration of the Canadian Lightning Detection Network (CLDN) and the U.S. National Lightning Detection Network (NLDN). Our summaries of annual lightning flash characteristics for the continental United States began in 1989 ( Orville 1991

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Liwei Jia, Thomas L. Delworth, Sarah Kapnick, Xiaosong Yang, Nathaniel C. Johnson, William Cooke, Feiyu Lu, Matthew Harrison, Anthony Rosati, Fanrong Zeng, Colleen McHugh, Andrew T. Wittenberg, Liping Zhang, Hiroyuki Murakami, and Kai-Chih Tseng

predict El Niño–Southern Oscillation (ENSO) and climate change, as well as the initialization of soil moisture. However, there is still a lack of studies quantifying how predictable the extremes are, and distinguishing the predictability sources for different types of extremes. To fill this gap, this study examines the seasonal prediction skill of the frequency of North American (area north of 23°N) summertime heat extremes at various lead times from 0 to 9 months, and explores the potential sources

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Wayne Higgins and David Gochis

1. The NAME Process Study The North American Monsoon Experiment (NAME) is an internationally coordinated process study aimed at determining the sources and limits of predictability of warm season precipitation over North America. The NAME program is jointly sponsored by the Climate Variability and Predictability (CLIVAR) and Global Energy and Water Cycle Experiment (GEWEX) interdisciplinary research efforts. NAME seeks improved understanding of the key physical processes that must be

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XiaoJing Jia, Hai Lin, and Jacques Derome

1. Introduction It is well known that some teleconnection patterns, such as the Pacific–North American (PNA) pattern and the North Atlantic Oscillation (NAO), can significantly influence the seasonal atmospheric conditions over North America ( Wallace and Guztler 1981 ; Barnston and Livezey 1987 ). The external forcing associated with sea surface temperature (SST) anomalies is known to play an important role in the variability of the PNA, and to a lesser extent of the NAO ( Horel and Wallace

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Yan Ge, Gavin Gong, and Allan Frei

1. Introduction Various prominent teleconnection patterns, such as El Niño–Southern Oscillation (ENSO), Pacific decadal oscillation (PDO), North Atlantic Oscillation (NAO), and Pacific–North American (PNA), are known to impact climate conditions over North America (NA), most notably during the Northern Hemisphere (NH) winter. These recurrent atmospheric circulation patterns are associated with variations in the intensity and location of the polar jet stream, the subtropical jet stream, or

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Alvaro Avila-Diaz, David H. Bromwich, Aaron B. Wilson, Flavio Justino, and Sheng-Hung Wang

average ( Walsh et al. 2017 ), is needed. Accurate representation of extremes across the Arctic is essential to the development of public policies, proper management of hydrological resources, and mitigation of impacts from human activity on the environment, as future projections over North America indicate a significant decrease in cold extremes and increase in warm extremes by the end of the twenty-first century ( Schoof and Robeson 2016 ; Lader et al. 2017 ; Sheridan and Lee 2018 ; Wazneh et al

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Alain Roberge, John R. Gyakum, and Eyad H. Atallah

1. Introduction Intense precipitation during the cold season on the North American west coast is believed to often be caused by poleward-traveling extratropical cyclones ( Lackmann and Gyakum 1999 ). The amount of water vapor and heat transported is so important that it may cause significant flooding in the mountains ( Colle and Mass 2000 ; Neiman et al. 2002 ; Ralph et al. 2006 ). This is caused by the combination of intense orographic precipitation and fast snowmelt, which may also initiate

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Toby R. Ault and Scott St. George

1. Introduction Recent studies have suggested that the risk of drought over North America changes at time scales of one to several decades, and that these changes are linked to variations in ocean temperatures. Enfield et al. (2001) found that summer rainfall in the continental United States is correlated with the Atlantic multidecadal oscillation (AMO), with less rain falling during the warm phase of the AMO. Similarly, McCabe et al. (2004) demonstrated that multidecadal drought frequency

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