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Michael D. Warner, Clifford F. Mass, and Eric P. Salathé Jr.

but cover only a relatively small portion of the circumference of the globe at any time. ARs are crucial components of the hydrologic cycle in many parts of the world, including western North America (e.g., Dettinger 2004 ; Ralph et al. 2006 , 2013 ; Neiman et al. 2011 ), western South America ( Viale and Nunez 2011 ), and Europe ( Sodemann and Stohl 2013 ; Lavers et al. 2013 ). Global mean atmospheric water vapor is projected to increase with surface warming at roughly the rate of Clausius

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Holger Fritze, Iris T. Stewart, and Edzer Pebesma

1. Introduction Surface water supplies throughout western North America hinge on a highly seasonal and variable mountain runoff pattern that is sensitive to climatic variability and change. While mountain regions in general contribute twice as much discharge to the terrestrial portion of the hydrologic cycle as the adjacent lowlands ( Viviroli et al. 2007 ), in western North America, the largest share of that precipitation is deposited between the months of October and March, resulting in a

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Andrew J. Newman and Richard H. Johnson

1. Introduction Gulf surge events, or surge events for short, are critical transient events in the North American monsoon (NAM) because they have been tied to moisture flux and precipitation anomalies during the NAM ( Anderson et al. 2000a ; Berbery 2001 ; Douglas and Leal 2003 ; Gochis et al. 2004 ; Higgins et al. 2004 ) and severe weather outbreaks in Arizona ( Maddox et al. 1995 ). Most of the large-scale features associated with the initiation of a surge event were first identified over

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Salvatore Pascale, Sarah B. Kapnick, Simona Bordoni, and Thomas L. Delworth

1. Introduction Convective activity developing during the summertime North American monsoon (NAM; e.g., Douglas et al. 1993 ; Adams and Comrie 1997 ; Higgins et al. 1997 ) accounts for a substantial fraction of the total annual precipitation in the southwestern United States (30%–50%) and northwestern Mexico (60%–80%). In these regions, the most severe rainfall events occur during the monsoon season, typically covering the period from July to September, and can cause flooding and life

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Long Yang, James Smith, Mary Lynn Baeck, and Efrat Morin

1. Introduction Flash floods in arid/semiarid regions are of great societal and environmental importance, and yet the hydrology, hydrometeorology, and hydroclimatology of flooding are still poorly understood (e.g., Higgins et al. 2003 ). In this study, we focus on storms that produce flash floods in the arid/semiarid southwestern United States. Much of this region receives more than half of its mean annual rainfall during the North American monsoon (NAM), which typically begins in late June or

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Jeanne M. Thibeault and Anji Seth

1. Introduction Warm-season precipitation [June–August (JJA)] is important to the economy and ecology of the midlatitude region of eastern North America, which encompasses the U.S. Northeast, southeastern Ontario, and southern Quebec [defined as 35°–50°N and 70°–80°W ( Fig. 1 ), which is referred to hereafter as the northeast region]. The northeast region is densely populated with large urban centers located preferentially along the coast, yet much of the region is rural, covered by forests or

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Ruth Cerezo-Mota, Myles Allen, and Richard Jones

1. Introduction The North American monsoon (NAM) is the regional-scale atmospheric circulation system ( Stensrud et al. 1997 ) responsible for the dramatic increase in precipitation during the summer in northwestern Mexico and the southwest United States ( Grantz et al. 2007 ). The NAM typically starts in mid-June in the core monsoon in northwestern Mexico ( Turrent and Cavazos 2009 ) and in early July in Arizona–New Mexico (AZNM) and finishes around the end of September (e.g., Douglas et al

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Hai Lin and Zhiwei Wu

1. Introduction Large-scale seasonal anomalies of near-surface air temperature ( T ) in North American (NA) winters have a significant impact on societal and economical activities. In the past several decades, both extreme cold and warm events have become more severe and frequent. For instance, the 2009/10 winter was noteworthy for its anomalously below-normal T ’s across much of the United States, whereas in Canada, it was the warmest and shortest winter within the past several decades. A

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Peter J. Rogers and Richard H. Johnson

1. Introduction The North American Monsoon (NAM) is an atmospheric circulation phenomenon characterized by an increase in convective activity and precipitation, beginning in early July and continuing through mid-September across northwest Mexico and the southwest United States ( Bryson and Lowry 1955 ; Douglas et al. 1993 ; Adams and Comrie 1997 ). Monsoon onset was originally attributed to the westward extension of the southeast United States subtropical high ( Jurwitz 1953 ; Bryson and

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J. Li, S. Sorooshian, W. Higgins, X. Gao, B. Imam, and K. Hsu

1. Introduction The North American monsoon (NAM) accounts for approximately 40%–80% of the annual rainfall in the southwestern United States and Mexico ( Douglas et al. 1993 ; Stensrud et al. 1995 ). As a consequence, it has a tremendous influence on the summer weather, climate, and water resources of this region. The NAM is characterized by numerous multiscale interactions, both in space and time. The climatological and synoptic features of the NAM have been studied systematically at the

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