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Zhenhai Zhang, David W. Pierce, and Daniel R. Cayan

et al. 2014 ), which expand forecast ensembles to include different dynamical models. The North American Multimodel Ensemble (NMME; Kirtman et al. 2014 ) is one of the primary examples of these collaborations. The NMME is a dynamical climate forecasting system using state-of-the-art coupled models from U.S. and Canadian modeling centers ( Kirtman et al. 2014 ). It provides a multimodel framework for assessing the subseasonal to seasonal forecast skill in dynamical models. This multimodel

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Kelsey M. Malloy and Ben P. Kirtman

negative phase of the 700-hPa geopotential height North Atlantic Oscillation (NAO), with a temporal correlation of −0.46. They also showed that the difference between the first two empirical orthogonal function modes of Great Plains LLJ variability depended on its connection to its moisture source, the Gulf of Mexico. Multiple studies suggested that a negative Pacific–North America (PNA) teleconnection has a strong influence on the Great Plains LLJ on pentad and/or monthly time scales ( Harding and

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Kelsey M. Malloy and Ben P. Kirtman

negative phase of the 700-hPa geopotential height North Atlantic Oscillation (NAO), with a temporal correlation of −0.46. They also showed that the difference between the first two empirical orthogonal function modes of Great Plains LLJ variability depended on its connection to its moisture source, the Gulf of Mexico. Multiple studies suggested that a negative Pacific–North America (PNA) teleconnection has a strong influence on the Great Plains LLJ on pentad and/or monthly time scales ( Harding and

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Michael J. Brennan and Sharanya J. Majumdar

assimilations in this paper are performed at 0000 UTC 9 September 2008. 3. Synoptic overview At 0000 UTC 8 September 2008, Hurricane Ike was located over eastern Cuba moving westward at 11 kt (1 m s −1 = 1.94 kt). North of Ike, a mid- and upper-level ridge axis extended from the western Atlantic across northern Florida and into the Gulf of Mexico, with a 200-hPa anticyclone centered over the extreme western Gulf ( Fig. 2a ). The midlatitude flow over North America showed a long-wave ridge over western

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David O. Blanchard

1. Introduction Occurrences of supercell thunderstorms producing widespread severe weather in northern Arizona are most likely to arise during the transition between the moist, subtropical environment of the warm-season North American monsoon regime (NAM; Adams and Comrie 1997 ) and the first, early season incursions of midlatitude baroclinic systems. The presence of copious tropical moisture, combined with steeper lapse rates, increased buoyant instability, and, more importantly, deep

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Peter Felsch and Woodrow Whitlatch

development or movement of stratus alongthe central California coast is developed and tested. Known as "stratus surges," these mesoscale events areinfrequently observed along the west coast of North America during the summer season. A subjective testinvolving inspection of visible image satellite photographs is successful in determining when the potential forsurge development exists. Objective tests based on Oakland, California, radiosonde data and alongshore pressuregradients at 0000 UTC are developed to

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Lynn A. McMurdie and Joseph H. Casola

assimilation ( Rabier 2005 ) and the ensemble Kalman filter ( Evenson 2003 ) continue to advance numerical weather prediction. Despite these hemispheric-scale improvements in the performance of numerical models, individual events of large short-term forecast errors still occur, especially near the west coast of North America and the offshore waters. McMurdie and Mass (2004) documented that the National Centers for Environmental Prediction’s (NCEP’s) Eta Model experienced large sea level pressure forecast

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

://mesonet.agron.iastate.edu/archive/ ). Precipitation data were acquired from the EC historical climate database (online at http://www.climate.weatheroffice.gc.ca/climateData/canada_e.html ). For the synoptic–dynamic analysis, we utilized the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR), which has a grid spacing of 32 km and 3-h temporal resolution ( Mesinger et al. 2006 ). To evaluate numerical model forecasts, we used the NCEP North American Mesoscale (NAM) model, which has a grid spacing of 12

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Cheng Zheng, Edmund Kar-Man Chang, Hyemi Kim, Minghua Zhang, and Wanqiu Wang

; Stockdale et al. 2010 ). El Niño–Southern Oscillation (ENSO) significantly modulates Northern Hemisphere (NH) ECA on interannual time scales ( Straus and Shukla 1997 ; Zhang and Held 1999 ; Eichler and Higgins 2006 ; Ma and Chang 2017 ). During El Niño years, an equatorward and eastward shift of boreal winter ECA is found over the Pacific, and ECA over North America weakens. The Madden–Julian oscillation (MJO) has significant impact on ECA over the North Pacific, the North Atlantic, and North America

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Kyle M. Nardi, Cory F. Baggett, Elizabeth A. Barnes, Eric D. Maloney, Daniel S. Harnos, and Laura M. Ciasto

convection ( Baggett et al. 2018 ), and the North American Monsoon ( Lorenz and Hartmann 2006 ). This modulation by the MJO extends to observed precipitation over North America ( Barrett et al. 2015 ; Baxter et al. 2014 ; Dong et al. 2018 ; Jones 2000 ; Jones and Carvalho 2012 ; Lin et al. 2010 ; Moon et al. 2012 ; Zhou et al. 2012 ). The QBO manifests as a 2–3-yr periodic cycle of downward propagating easterly and westerly wind regimes in the equatorial stratosphere ( Baldwin et al. 2001 ). Like

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