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Lars Wiegand, Arwen Twitchett, Cornelia Schwierz, and Peter Knippertz

assessing such limitations than deterministic forecasts alone ( Tracton and Kalnay 1993 ). To represent initial condition uncertainties, different methods are used. The European Centre for Medium-Range Weather Forecasts (ECMWF) uses singular vectors to achieve maximum perturbation growth for a given (48 h) optimization time ( Palmer et al. 1992 ). The National Centers for Environmental Prediction (NCEP) use the ensemble transform technique ( Wei et al. 2008 ), which is an improved version of the

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Paraskevi Giannakaki and Olivia Martius

introduce a tool for the quantification and characterization of errors in the representation of synoptic-scale Rossby waveguides, that is, areas of elongated strong PV gradients that are collocated with the jet streams and the dynamical tropopause in forecast data. Numerous object-based verification techniques have been developed in recent years [see Gilleland et al. (2009) and Jolliffe and Stephenson (2012) for details]. Here, we modify the Method for Object-based Diagnostic Evaluation (MODE

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Lisa-Ann Quandt, Julia H. Keller, Olivia Martius, and Sarah C. Jones

1. Introduction As atmospheric blocking may cause high-impact weather like heat waves and flooding (e.g., Matsueda 2009 ), there is a special interest in its predictability and the physical processes that limit forecast quality. Blocking is a large-scale flow pattern that decelerates arriving eddies, as well as the background flow, and forces them to follow a more meridional direction (e.g., Rex 1950 ; Arakawa 1952 ; Sumner 1954 ). Atmospheric blocking is persistent and self-sustaining (e

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Florian Harnisch and Martin Weissmann

1. Introduction Tropical cyclones (TCs) usually develop over data-sparse regions of the tropical oceans. The limited number of observations and the rapid development of TCs increases uncertainties of the model analysis in these regions, which can lead to significant forecast errors ( Langland 2005 ). Surveillance programs deploying dropsonde observations in and around TCs have been operated for the Atlantic ( Burpee et al. 1996 ; Aberson 2002 ) and the western North Pacific basin ( Wu et al

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Kirstin Kober, Annette M. Foerster, and George C. Craig

be obtained by postprocessing. The results would depend on the methods used, but quite sophisticated techniques based on spatial statistics are being developed ( Scheuerer 2014 ). On the other hand, if there are significant dynamical feedbacks from the convective variability onto the larger-scale flow, there is potential for a physically based parameterization to improve an ensemble forecast in ways that postprocessing could not. This too is an important topic for future research. Acknowledgments

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Julia H. Keller

; Torn 2010a ; Keller et al. 2014 ; Quinting and Jones 2016 ). To the author’s knowledge, the present study is the first that combines the two analysis techniques to make use of the analysis for an operational EPS in a way that goes beyond the investigation of several forecast scenarios. The paper is organized as follows. Section 2 introduces the database used in the study, while an outline of the analysis methods is provided in section 3 . The investigation and interpretation of the results

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Julia H. Keller, Sarah C. Jones, and Patrick A. Harr

to identify the dominant processes during the interaction, describe their representation in the scenarios and thus elucidate their influence on the distinct developments. After a brief introduction of the analysis technique and the selection of particular ensemble members in the next section, an overview of the two tropical cyclones is provided in section 3 . We then analyze the different forecast scenarios for the ET of the two storms using the K e framework ( section 4 ). Conclusions are

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Andreas Schäfler, Andreas Dörnbrack, Christoph Kiemle, Stephan Rahm, and Martin Wirth

1. Introduction During the last few decades, forecasts of operational numerical weather prediction (NWP) models have continuously improved as a result of an enhanced spatial resolution and advanced parameterization schemes for the model physics. Furthermore, the global coverage of spaceborne remote sensing observations and their assimilation has rapidly improved the forecast skill ( Simmons and Hollingsworth 2002 ). However, the representation of cloud processes involving the condensation of

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Julian F. Quinting and Sarah C. Jones

wave dispersion. The dispersion of Rossby waves into downstream regions has the ability to cause surface cyclogenesis ( Agusti-Panareda et al. 2004 ; Cordeira and Bosart 2010 ) or high-impact weather events such as severe precipitation (e.g., Martius et al. 2008 ; Grams et al. 2011 ; Grams and Blumer 2015 ). Furthermore, initial perturbations and ET-related forecast uncertainties tend to grow and spread into downstream regions in connection with the development of midlatitude Rossby wave

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Julia H. Keller, Christian M. Grams, Michael Riemer, Heather M. Archambault, Lance Bosart, James D. Doyle, Jenni L. Evans, Thomas J. Galarneau Jr., Kyle Griffin, Patrick A. Harr, Naoko Kitabatake, Ron McTaggart-Cowan, Florian Pantillon, Julian F. Quinting, Carolyn A. Reynolds, Elizabeth A. Ritchie, Ryan D. Torn, and Fuqing Zhang

research on the representation of model errors arising from diabatic processes using techniques such as stochastic physics. The research summarized in this review primarily focused on assessing the impact of ET on the short-to-medium-range forecast horizon. Preliminary results reveal a statistically significant correlation between monthly mean values of selected teleconnection indices and ET event counts, as well as significant departures from climatology on the subseasonal to seasonal time scale in

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