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  1. Abstract Thunderstorms that produce hail accumulations at the surface can impact residents by obstructing roadways, closing airports, and causing localized flooding from hail-clogged drainages. These storms have recently gained an increased interest within the scientific community. However, differences that are observable in real time between these storms and storms that produce nonimpactful hail accumulations have yet to be documented. Similarly, the characteristics within a single storm that are useful to quantify or predict hail accumulations are not fully understood. This study uses lightning and dual-polarization radar data to characterize hail accumulations from three storms that occurred on the same day along the Colorado–Wyoming Front Range. Each storm’s characteristics are verified against radar-derived hail accumulation maps and in situ observations. The storms differed in maximum accumulation, either producing 22 cm, 7 cm, or no accumulation. The magnitude of surface hail accumulations is found to be dependent on a combination of in-cloud hail production, storm translation speed, and hailstone melting. The optimal combination for substantial hail accumulations is enhanced in-cloud hail production, slow storm speed, and limited hailstone melting. However, during periods of similar in-cloud hail production, lesser accumulations are derived when storm speed and/or hailstone melting, identified by radar presentation, is sufficiently large. These results will aid forecasters in identifying when hail accumulations are occurring in real time. 
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  2. null (Ed.)
    This paper reviews the evolution of planetary boundary layer (PBL) parameterization schemes that have been used in the operational version of the Hurricane Weather Research and Forecasting (HWRF) model since 2011. Idealized simulations are then used to evaluate the effects of different PBL schemes on hurricane structure and intensity. The original Global Forecast System (GFS) PBL scheme in the 2011 version of HWRF produces the weakest storm, while a modified GFS scheme using a wind-speed dependent parameterization of vertical eddy diffusivity (Km) produces the strongest storm. The subsequent version of the hybrid eddy diffusivity and mass flux scheme (EDMF) used in HWRF also produces a strong storm, similar to the version using the wind-speed dependent Km. Both the intensity change rate and maximum intensity of the simulated storms vary with different PBL schemes, mainly due to differences in the parameterization of Km. The smaller the Km in the PBL scheme, the faster a storm tends to intensify. Differences in hurricane PBL height, convergence, inflow angle, warm-core structure, distribution of deep convection, and agradient force in these simulations are also examined. Compared to dropsonde and Doppler radar composites, improvements in the kinematic structure are found in simulations using the wind-speed dependent Km and modified EDMF schemes relative to those with earlier versions of the PBL schemes in HWRF. However, the upper boundary layer in all simulations is much cooler and drier than that in dropsonde observations. This model deficiency needs to be considered and corrected in future model physics upgrades. 
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