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Robert Conrick, Clifford F. Mass, and Qi Zhong

idealized or dry models. Large-eddy simulation (LES) experiments have investigated KH instability in a variety of real-world cases, including in a mesoscale convective system (MCS) over southern England ( Browning et al. 2012 ), within a hurricane boundary layer ( Nakanishi and Niino 2012 ; Na et al. 2014 ), during frontogenesis ( Samelson and Skyllingstad 2016 ), and for stratified flow over terrain ( Sauer et al. 2016 ). Recent studies have used full-physics NWP models to simulate KH waves. Mahalov

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Chanh Kieu, Vijay Tallapragada, Da-Lin Zhang, and Zachary Moon

, experimental real-time TC forecasts conducted by the U.S. National Centers for Environmental Prediction (NCEP) Environmental Modeling Center (EMC) during 2012–14 for the northwestern Pacific (WPAC) basin using the Hurricane Weather Research and Forecasting Model (HWRF) provide a unique opportunity to examine this type of DWC structure more systematically. In general, TCs in the WPAC basin experienced more often rapid intensification, larger storm sizes, and stronger intensity than those occurring over the

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R. A. Maddox, D. J. Perkey, and J. M. Fritsch

period of only 6 h. It is hypothesized that the convective system is responsiblefor these changes. The question of whether the diagnosed changes reflect a natural evolution of largescale meteorological fields or are a result of widespread deep convection is considered utilizing twoseparate numerical forecasts produced by the Drexel-NeAR mesoscale primitive equation model. A"dry" forecast, in which no convective clouds are permitted, is considered representative of the evolution of the large

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Da-Lin Zhang and J. Michael Fritsch

forecast verifying at 1500 GMT 19 July 1977.15 SEPTEMBER 1986DA-LIN ZHANG AND J. MICHAEL FRITSCH1927FIG. I3a. Mesoscale analysis for 1800 GMT 19 July 1977 (adaptedfrom H78). Heavy dashed lines indicate troughs. Cold and warinfrontal symbols alternated with double dots indicate moistdowndraftoutflow boundaries. The light shading denotes the level-1 radar echoesand the dark shading denotes level-3 (or greater) radar echoes. Reflectivity boundary isnot defined if the echo contour is open. A fullwind

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Madalina Surcel, Isztar Zawadzki, and M. K. Yau

need to assess the uncertainty associated with a given forecast, which can be done through ensemble forecasting. Ensemble forecasting techniques for medium- to long-range weather prediction in midlatitudes, which is mostly affected by synoptic-scale baroclinic instabilities, are well established by now ( Kalnay 2003 , section 6.5). On the other hand, the mesoscale details of weather, such as the evolution of precipitation systems, are affected by moist convective processes. Since computational

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Zhaoxia Pu, Shixuan Zhang, Mingjing Tong, and Vijay Tallapragada

. 2009 ; Zhang et al. 2011 ). At the National Centers for Environmental Prediction (NCEP), the Hurricane Weather Research and Forecasting Model (HWRF) ( Tallapragada et al. 2014 ) has provided regional mesoscale hurricane intensity and track forecasts since 2007. It has provided real-time TC forecasts to the NHC for the Atlantic and eastern North Pacific basins since it became operational at NCEP in the 2007 hurricane season and then extended to all global oceanic basins in 2014. A vortex

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D. L. A. Flack, P. A. Clark, C. E. Halliwell, N. M. Roberts, S. L. Gray, R. S. Plant, and H. W. Lean

via more accurate initial conditions, whereas if the errors on the large scale are small then, regardless of improvements in initial conditions, there will be limited improvement in the forecasts on the mesoscale. This result was also found by Durran and Gingrich (2014) and Weyn and Durran (2017) , though the latter study notes that there is no upscale/downscale growth within their idealized simulations and the errors grow up-amplitude on all scales simultaneously. These discrepancies show that

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Christopher Melhauser and Fuqing Zhang

1. Introduction Understanding the sources of forecast uncertainties and error growth dynamics in numerical weather prediction of squall lines, bow echoes, and other mesoscale convective systems (MCSs) may be essential in predicting severe weather, both deterministically and probabilistically. It is well documented that convective cells forming in favorable environmental conditions can be organized into a linear squall line, with subsequent bow echo formation producing damaging straight

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Michael L. Kaplan and Douglas A. Paine

been developed in an effort to simulate the interaction bet~veen quasi-geostrophicand mesoscale forcing. Initializations performed at 127 km with either a diagnostic omega equation orbarotropic forecast are followed by a prediction with a moist nine-level primitive equation model at 32 km.Several integrations are performed utilizing both real and artificial data for the problem of the waterinduced heat island in the cold season. The results of these integrations indicate important variations inboth

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F. Zhang, Chris Snyder, and Richard Rotunno

known about the mechanisms by which small-scale errors grow and influence larger scales. In this paper, we investigate through integrations of a high-resolution regional NWP model the hypotheses that moist convection is a primary mechanism for forecast-error growth at sufficiently small scales, and that convective-scale errors contaminate the mesoscale within lead times of interest to NWP, thus effectively limiting the predictability of the mesoscale. Existing demonstrations of the limit of

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