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Nicholas J. Schiraldi and Paul E. Roundy

, the anomalous ridge over China is more amplified, and there is no anomalous trough present in the Gulf of Alaska ( Figs. 3c,d ). Both the drought decay and onset transitions favor wave breaking associated with the ridge over Alaska. Through anticyclonic wave breaking, a trough is injected into the tropics, aiding in the organization of convection over the eastern Pacific Ocean ( Matthews and Kiladis 1999 ; MacRitchie and Roundy 2016 ). The similarity over North America between the low

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Arthur V. Douglas, Daniel R. Cayan, and Jerome Namias

DECEMBER 1982 DOUGLAS, CAYAN AND NAMIAS 1851Large-Scale Changes in North Pacific and North American Weather Patterns in Recent DecadesI ARTHUR V. DOUGLASDepartment of Atmospheric Sciences, Creighton University, Omaha, NE 68178 DANIEL R. CAYAN AND JEROME NAMIASScripps Institution of Oceanography, University of California, San Diego, La Jolla 92093(Manuscript'received 28

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Kevin A. Biernat, Lance F. Bosart, and Daniel Keyser

beneath TPVs suggests that TPVs may be effective in triggering CAOs. TPVs (e.g., Hakim and Canavan 2005 ; Cavallo and Hakim 2009 , 2010 , 2012 ; Szapiro and Cavallo 2018 ), and 500-hPa cyclones (e.g., Bell and Bosart 1989 ) and 500-hPa troughs (e.g., Sanders 1988 ; Lefevre and Nielsen-Gammon 1995 ), in which some TPVs may be embedded (e.g., Shapiro et al. 1987 ), have been shown to frequently occur over central and eastern North America. Similarly, CAOs have been shown to frequently occur

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Pierre Gauthier, Monique Tanguay, Stéphane Laroche, Simon Pellerin, and Josée Morneau

results show a positive impact with 4DVAR, particularly for winds. The impact on the forecast at longer range has been independently evaluated for both the summer and winter periods. Verification against radiosonde data showed that the forecasts based on 4DVAR were improved over North America. The improvement was noted particularly over the west coast of North America at short ranges. This is illustrated by Fig. 9 showing the verification over this region and the whole Northern Hemisphere for the

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Gonzalo Miguez-Macho and Jan Paegle

adaptive targeting since locally enhanced observational coverage would no longer be effective. In this paper we focus on predictions over North America and investigate the effect of initial uncertainty in regions that include the North American domain itself, the northeastern Pacific and the complete North Pacific. The selected areas are fixed, and this represents a fundamental difference with other work relating the influence of local errors on regional forecasts. The size of the studied regions

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Jason C. Shafer and W. James Steenburgh

the 2002 Tax Day Storm (15 April) produced dramatic temperature falls of 7°C in 10 s and 19°C in 2 h, wind gusts of more than 30 m s −1 , and $2 million in property damage ( NCDC 2002 , p. 243). Previous studies of cold fronts over western North America are limited primarily to landfalling Pacific fronts (e.g., Elliott 1958 ; Hobbs et al. 1980 ; Hobbs and Persson 1982 ; Reynolds and Kuciauskas 1988 ; Braun et al. 1997 ; Colle et al. 1999 ; Yu and Smull 2000 ; Chien et al. 2001 ) and cold

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Robert R. Dickson and Jerome Namias

OCTOBEal976 ROBERT R. DICKSON AND JEROME NAMIAS 1255North American Influences on the Circulation and Climate of the North Atlantic Sector ROBERT R. DICKSON~ Fisheries Laboratory, Lowestoft, Suffolk, England J~.xoM~. NAMmSScripps Institution of Oceanography, La Jolla, Calif. 92093(Manuscript received 30 April 1976)ABSTRACT During the post-war period the pressure field

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. DENDROCLIMATIC ANALYSIS OF WESTERN NORTH AMERICATree-ring chronologies from 26 stations through westernNorth America were selected for their location, length,and reliability (table 7). Douglas-f?r chronologies weregenerally selected, but in some areas, the best chronologiesavailable were for other species. All chronologies wereconverted to standardized ring-width indices, so theyare relatively free of changes arising from growth andmaturation of individual trees.Whenever possible, chronologies

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T. J. Blasing and G. R. Lofgren

700 MONTHLY WEATHER REVIEW VOLUME 108Seasonal Climatic Anomaly Types for the North Pacific Sector and Western North America T. J. BLASINGEnvironmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37850 G. R. LOFGRENLaboratory of Tree-Ring Research, University of Arizona, Tucson 85721(Manuscript received 25 May 1979, in final form

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Bruno Z. Ribeiro and Lance F. Bosart

. The Rockies in North America (NA; e.g., Carlson and Ludlam 1968 ; Banacos and Ekster 2010 , hereafter BE10 ) and the Tibetan Plateau in East Asia (e.g., Das et al. 2014 ) are known to favor the formation of EMLs that can have a great impact on the atmospheric conditions over the lower terrain downstream due to their association with hazardous weather events ( Cordeira et al. 2017 ). Observations and case studies by Rasmussen and Houze (2016) show EMLs occur east of the Andes in South America

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