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B. Timbal, R. Kounkou, and G. A. Mills

during the winter months from May to September, and are known locally as cool-season tornadoes (CSTs). Although associated with large thunderstorms or deep convective clouds, Hanstrum et al. (2002) showed that CSTs occurred in a large-scale environment, which differs from that for summer tornadoes; they form in a combination of less (but still) positively buoyant and high low-level vertical wind shear environments. While individual events remain nearly impossible to forecast at any scale outside

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Shawn M. Milrad, Eyad H. Atallah, and John R. Gyakum

1. Introduction Atlantic Canada ( Fig. 1 ), and more specifically, St. John’s, Newfoundland (CYYT), is a location susceptible to extreme precipitation events, particularly in the cool season ( Stewart et al. 1987 ), defined in Milrad et al. (2009) as October–April. Located at the confluence of several North American storm tracks ( Milrad et al. 2009 ) and near the convergence zone of the cold southward-flowing Labrador Current and the warm northward-flowing Gulf Stream current ( Aguado and

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Erick R. Rivera, Francina Dominguez, and Christopher L. Castro

during November 2003. The work by Dettinger et al. (2011) shows that the contribution of ARs to the total cool season precipitation in the Southwest, particularly in several portions of Arizona and New Mexico, during the water years 1998–2008 is less than 10%. However, their analysis only took into account the ARs that made landfall between 32.5°N (international United States–Mexico border) and 52.5°N. In a following study, Rutz and Steenburgh (2012) argue that this percentage is underestimated

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Heather M. Archambault, Lance F. Bosart, Daniel Keyser, and Anantha R. Aiyyer

the Gulf Coast and southeastern United States ( Leathers et al. 1991 ; Notaro et al. 2006 ). Building upon prior research linking recurrent large-scale flow regimes to regional precipitation patterns in the extratropical NH, the present study examines the influence of large-scale flow regimes on cool-season precipitation in the northeastern United States (Northeast) from 1948 through 2003. This study consists of (i) a statistical analysis of cool-season Northeast precipitation during NAO and PNA

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Shawn M. Milrad, Eyad H. Atallah, and John R. Gyakum

identified, as was the case at the locations mentioned above, the local forecaster is able to use these benchmarks in addition to whatever forecast model(s) he or she is using. Extreme precipitation events are prevalent and important in Atlantic Canada, where storms often cause hardship ( Stewart et al. 1987 ), especially in the cool season (defined here as October–April). Atlantic Canada ( Fig. 1 ), made up of the provinces of New Brunswick, Prince Edward Island, Nova Scotia, and Newfoundland and

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Heather M. Archambault, Daniel Keyser, and Lance F. Bosart

-frequency atmospheric variability, substantially modulate the amount of precipitation received by Europe and central North America, respectively. While the relationship is more subtle, these low-frequency modes also affect precipitation in the northeastern United States (NE; e.g., Leathers et al. 1991 ; Hurrell 1995 ; Coleman and Rogers 2003 ; Notaro et al. 2006 ; Archambault et al. 2008 ). The NAO and PNA affect cool-season NE precipitation because the NAO and PNA phases are linked to the strength and

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N. S. Oakley, J. T. Lancaster, B. J. Hatchett, J. Stock, F. M. Ralph, S. Roj, and S. Lukashov

). We address the following questions: What parts of California most frequently experience OTPEs, and where are OTPEs rarely observed? How frequently do OTPEs occur after a specific seasonal rainfall total has been exceeded? How are OTPEs distributed within the cool season? Are OTPEs driven by atmospheric rivers? California’s soils are rarely susceptible to shallow landsliding during the dry season, when soil moisture is at its lowest. During the October–May period, when California receives most of

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William V. Sweet and Chris Zervas

1. Introduction Sea levels vary on many time and space scales. Important short-period variations occur when water levels differ significantly from those driven by localized tidal dynamics. Along the East Coast, these events are a cause for concern whether they are multiday storm surges from regional East Coast extratropical cool-season storms, commonly referred to as nor’easters , or as more localized impacts from hurricanes. Both types of storm surges can cause extensive flooding, erosion

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Andrew C. Winters, Lance F. Bosart, and Daniel Keyser

1. Introduction The occurrence of extreme temperature events (ETEs) during the cool season (September–May) is often accompanied by considerable societal and economic impacts. Extreme cold events, in particular, are responsible for about 30 deaths per year in the United States ( NWS 2018 ), can result in substantial damage to infrastructure (e.g., Cellitti et al. 2006 ), and can induce agricultural and economic losses (e.g., Rogers and Rohli 1991 ; Gu et al. 2008 ; Dole et al. 2014 ; Wolter

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Jian Zhang, Youcun Qi, David Kingsmill, and Kenneth Howard

1. Introduction The topography of the western United States poses a significant challenge in creating physically realistic and spatially accurate estimates of precipitation using remote sensing techniques. Simply stated, complex terrain serves as a hostile observing environment for radars of any size and wavelength. This is further compounded by the presence of complex microphysical processes during the cool season as a result of air–sea interactions within coastal regions as well as the

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