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Martin Hoerling, James Hurrell, Arun Kumar, Laurent Terray, Jon Eischeid, Philip Pegion, Tao Zhang, Xiaowei Quan, and TaiYi Xu

1. Introduction Physical factors determining the predictability of decadal climate over land include sensitivities to external radiative forcing, to local and remote surface boundary forcing, and to unforced variability associated with atmospheric noise. In this study, the contribution of these factors to decadal variability is estimated in the context of producing a probabilistic forecast of 10-yr averaged 2011–20 North American surface air temperature and precipitation. Our analysis of

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Alicia M. Bentley, Lance F. Bosart, and Daniel Keyser

association with damaging winds and heavy precipitation (e.g., Salmon and Smith 1980 ; Gyakum 1983a , b ; Uccellini et al. 1984 , 1985 ; Hakim et al. 1995 , 1996 ; Mailier et al. 2006 ; Dacre et al. 2012 ). Particularly strong ECs forming over and traversing densely populated regions of central and eastern North America have the potential to lead to extreme weather events (EWEs), defined in the present study as high-impact weather events that are societally disruptive, geographically widespread

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Juan M. Lora

projected future changes ( Kageyama et al. 2017 ). Moreover, proxy reconstructions of the LGM climate are relatively abundant ( Prentice et al. 2000 ; Braconnot et al. 2012 ; MARGO Project Members 2009 ; Bartlein et al. 2011 ), and many studies have specifically focused on model–data comparisons ( COHMAP Members 1988 ; Bartlein et al. 1998 ; Otto-Bliesner et al. 2009 ; Braconnot et al. 2012 ; Hargreaves et al. 2013 ; Scheff et al. 2017 ). In North America, the differences between the LGM and

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Andrew C. Winters, Daniel Keyser, Lance F. Bosart, and Jonathan E. Martin

climatology of Northern Hemisphere jet superpositions using the NCEP–NCAR reanalysis dataset ( Kalnay et al. 1996 ; Kistler et al. 2001 ) during November–March 1960–2010 indicates that jet superpositions are most frequent over the western North Pacific, North America, and northern Africa ( Christenson et al. 2017 ). The key dynamical processes associated with western North Pacific jet superpositions have been examined in detail by Handlos and Martin (2016) . These dynamical processes include equatorward

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Richard Seager, Jennifer Nakamura, and Mingfang Ting

national economy. Often not recognized, drought also has serious impacts on the mental health of farming families and people in agricultural communities with long-lasting effects [see U.S.-based review by Vins et al. (2015) ]. Improved understanding and forecasting of drought at least provides the possibility of improved anticipation of, and adaptation to, drought conditions with potential benefits for people and society. Understanding the physical causes of droughts in North America, and the relative

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Stephen W. Bieda III, Christopher L. Castro, Steven L. Mullen, Andrew C. Comrie, and Erik Pytlak

1. Introduction The frequent presence of upper-tropospheric lows in the subtropical North Pacific and North Atlantic during boreal summer is well documented (e.g., Riehl 1948 ; Kelley and Mock 1982 ). Of specific interest to the summer climate of North America are warm core upper-tropospheric lows that develop in the Gulf of Mexico and Atlantic in or near the tropical upper-tropospheric trough (TUTT) that, according to Whitfield and Lyons (1992) , is a climatological mean summer circulation

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Rachel R. McCrary and Linda O. Mearns

1. Introduction Seasonal snow cover is an important component of the climate of North America. It plays a direct role in the surface energy budget through its high albedo and low thermal conductivity, which have important implications for the snow–albedo feedback ( Qu and Hall 2007 ) and permafrost ( Lawrence and Slater 2010 ). The spatial extent of snow cover over North America influences the atmospheric circulation on monthly to seasonal time scales ( Cohen and Entekhabi 2001 ; Sobolowski et

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Enrique R. Vivoni, Kinwai Tai, and David J. Gochis

such region is the southwest United States, where summer convective rainfall is promoted and evapotranspiration (ET) is sensitive to soil moisture during the North American monsoon (NAM; Hong and Pan 2000 ; Kurc and Small 2007 ; Vivoni et al. 2007c , 2008b ). In this region, high soil moisture tends to lower surface albedo and the Bowen ratio (i.e., sensible to latent heat flux ratio), which in turn increases net radiation ( Zheng and Eltahir 1998 ; Eltahir 1998 ). The increase of total

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J. Craig Collier and Guang J. Zhang

1. Introduction During the twentieth century, the North American monsoon system became recognized as a significant climate regime in the southwestern United States and northwestern Mexico. Among the earliest written reports of a monsoonlike climate in this region are those of Campbell (1906) and Blake (1923) , who document the existence of “Sonora storms” that prevail over the mountains and deserts of southern California from July into early October. As early as there have been

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Toby R. Ault, Alison K. Macalady, Gregory T. Pederson, Julio L. Betancourt, and Mark D. Schwartz

fighting fires or managing insect outbreaks. In addition, improved ecological understanding and advance knowledge of how spring onset is likely to vary on decadal time scales could guide strategic investments in invasive species removal, forest harvesting and replanting, and assisted migration. Here, we investigate the role of dominant modes of atmospheric variability in modulating spatial and temporal variability in spring onset across western North America (WNA) over the past century. More

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