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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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Tracy Ewen, Andrea Grant, and Stefan Brönnimann

America during the early twentieth century, for example, the Dust Bowl droughts in the 1930s. The processes involved in this drought, which affected the southern United States and the Great Plains regions, cannot be fully understood with available surface data. Data from higher levels in the atmosphere are required in order to understand the dynamical processes that govern large-scale circulation and the corresponding effects on surface climate over North America. In this paper, we present a monthly

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Andrew E. Mercer and Michael B. Richman

were similar in track density (number of storms per spatial unit) and therefore, no particular one is superior. Thus, NCEP–NCAR reanalysis data was selected for the raw variable extraction since it was used for creation of the CDC storm track dataset. Raw variables were extracted from the dataset at numerous pressure levels on a 2.5° latitude–longitude grid for most of North America. According to Kalnay et al. (1996) , the reanalysis dataset can be divided into several classes based on the

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Jessica K. Turner, John Gyakum, and Shawn M. Milrad

sounding, to simulate the formation of arctic air. Emanuel (2008) showed that the rate and depth of the cooling were sensitive to the amount of water vapor, condensate, and clouds. When clouds were allowed to form, air in contact with the cloud top cooled through radiation, while warming the lower layers through radiation and latent heat release. High-latitude northwestern North America is observed to be warming, especially during the winter season ( Jones and Moberg 2003 ; Serreze and Francis 2006

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Carl J. Schreck III, Jason M. Cordeira, and David Margolin

1. Introduction The Madden–Julian oscillation's (MJO; Madden and Julian 1994 ; Zhang 2005 ) convection can initiate and amplify Rossby wave trains ( Matthews et al. 2004 ; Roundy et al. 2010 ; Weare 2010 ) that manifest themselves in teleconnections such as the North Atlantic Oscillation (NAO; Cassou 2008 ; Lin et al. 2009 ) and the Pacific–North American (PNA) patterns ( Kiladis and Weickmann 1992 ; Higgins and Mo 1997 ; Moore et al. 2010 ). The interactions between the MJO and the

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

2016 ). To characterize this variability, Winters et al. (2020) conducted a climatological analysis of North American jet superposition events by classifying events in the National Centers for Environmental Prediction Climate Forecast System Reanalysis (CFSR; Saha et al. 2010 ) based on the extent to which the polar and subtropical jets deviated from their respective climatological locations to form a superposition. “Polar dominant” events were classified as those events in which the polar jet

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Ron McTaggart-Cowan, Lance F. Bosart, John R. Gyakum, and Eyad H. Atallah

; Atallah et al. 2007 ), and modeling studies ( McTaggart-Cowan et al. 2003 ; Colle 2003 )]. Recent work by Anwender et al. (2006) and Harr et al. (2006) has shown that ET events—in particular those that lead to redevelopment—present a significant challenge to both deterministic and ensemble forecasting systems. Harr et al. (2006) demonstrate that uncertainty associated with transitioning systems in the western North Pacific Ocean can readily impact medium-range forecasts over North America

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Guillem Candille

exchange their ensemble data in order to build a global multiensemble. North America endows itself with its own multiensemble. This paper presents a study on the North American Ensemble Forecast System (NAEFS). That multiensemble project was born in February 2003 when the National Oceanic and Atmospheric Administration (NOAA), the Meteorological Service of Canada (MSC), and the National Meteorological Service of Mexico concluded a high-level agreement about joint ensemble research and development work

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AUGVST, 1919 MONTHLY WEATHER REVIEW.WEATHER OF THE MONTH.WEATHER OF NORTH AMERICA AND ADJACENT OCEANS.583GENERAL CONDITIONS.By A. J. HENRY, Meteorologist.The ocean highs which become firmly established in the Northern Hemisphere in July begin to contract in area and the baronietric level begins to i n k in August av continental prevsures increare somewhat. The continen- tal low pre3sure of Asia increases 0.05 to 0.10 incher, and in general the annual swing in the pressure from summer to winter

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APRIL, 1919. MONTHLY WEATHER REVIEW. 255THE WEATHER OF THE MONTH.WEATHER OF NORTH AMERICA AND ADJACENT OCEANS.GENERAL CONDITIONS.A. J. HENRY, Meteorologist.The distribution of mean pressure in the Northern Hemisphere for April indicates the beginning of the dis- solution of the great continental hi lis antl the buildingNorth Atlantic and the Aleutian LOW of the North Pacific, respectively, are still in evidence, although the former now estends southwestward almost to the Canadian Maritime

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