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Russ S. Schumacher, Deanna A. Hence, Stephen W. Nesbitt, Robert J. Trapp, Karen A. Kosiba, Joshua Wurman, Paola Salio, Martin Rugna, Adam C. Varble, and Nathan R. Kelly

from vehicles that were positioned in advance of each RELAMPAGO IOP by the mission scientists. Detailed observing strategies were designed with the expected weather conditions and the scientific objectives of the particular mission in mind. Previous experiences in the Mesoscale Predictability Experiment (MPEX; Trapp et al. 2016 ) and Plains Elevated Convection At Night (PECAN; Geerts et al. 2017 ; Hitchcock et al. 2019 ) projects, along with the availability of suitable roads and launch

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T. Connor Nelson, James Marquis, Adam Varble, and Katja Friedrich

observed decrease in CIN between Fail and CI events is due to factors such as steady destabilizing of the capping inversion from local mesoscale lift, moistening and cooling of the lower free troposphere from detrainment of cumulus, or deepening of the convective boundary layer. While the mean Fail environments indicate conditions that are generally less favorable for initiating and sustaining convection, CAPE, subcloud wind shear, LFC height, IB, and CIN (surface or MU) are not statistically different

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Jake P. Mulholland, Stephen W. Nesbitt, Robert J. Trapp, and John M. Peters

and a uniform vertical grid spacing of 250 m over a domain with dimensions 324 × 504 × 20 km 3 (648 × 1008 × 80 grid points). Sensitivity test simulations conducted with a uniform horizontal grid spacing of 250 m, a uniform vertical grid spacing of 125 m, and a vertical dimension of 24 km for the 4500 m terrain configuration showed little difference in convective morphology, 1 thus supporting the use of a relatively coarser resolution and shallower domain. The lower boundary condition was

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Robert J. Trapp, Karen A. Kosiba, James N. Marquis, Matthew R. Kumjian, Stephen W. Nesbitt, Joshua Wurman, Paola Salio, Maxwell A. Grover, Paul Robinson, and Deanna A. Hence

representative of an average of the lowest 100-hPa of the atmosphere from each sounding are shown with dotted lines. One of the forecast uncertainties during IOP4 was the geographical location and timing of the initiation of deep convection, especially given the strength of the capping inversion and associated convective inhibition (CIN) present in the 1200 UTC soundings ( Fig. 3 ). Parcel lifting was expected in association with horizontal moisture convergence along an east–west-oriented mesoscale boundary

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Hernán Bechis, Paola Salio, and Juan José Ruiz

1. Introduction In a broad sense, the literature defines drylines as airmass boundaries characterized by a sharp horizontal contrast in the low-level humidity fields ( Owen 1966 ; Schaefer 1974 ). Those that form over the Great Plains of the United States are the most widely studied and are considered as a preferential zone for convection initiation ( Wilson and Roberts 2006 ) which can lead, under favorable conditions, to severe weather events ( Lin 2007 ). Drylines are also found in other

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Sujan Pal, Francina Dominguez, María Eugenia Dillon, Javier Alvarez, Carlos Marcelo Garcia, Stephen W. Nesbitt, and David Gochis

et al. 2019 ) and also used for twice-daily operational forecasting during RELAMPAGO IOPs. We used different meteorological data as initial and boundary conditions to force WRF ( Table 1 ). For example, ERA5–WRF uses ERA5 data as forcing for WRF. Similarly, GFS–WRF uses GFS while local ensemble transform Kalman filter (LETKF)–WRF uses GFS+GEFS (Global Ensemble Forecast System) for the boundary conditions (see Table 1 ). WRF generated precipitation was interpolated to WRF-Hydro grid (1 km) to

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Jake P. Mulholland, Stephen W. Nesbitt, and Robert J. Trapp

(LLJ), and upper-level negative geostrophic potential vorticity (weak ambient inertial instability) all favored the most rapid transition of discrete convective cells into an MCS. Furthermore, Dial et al. (2010) found that for cases of convection initiation (CI) along a frontal or similar boundary, the potential for UCG increased when the cloud-layer wind and deep-layer vertical wind shear vectors were nearly parallel to the initiating boundary. Additionally, as the magnitude of low-level forcing

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Matthew R. Kumjian, Rachel Gutierrez, Joshua S. Soderholm, Stephen W. Nesbitt, Paula Maldonado, Lorena Medina Luna, James Marquis, Kevin A. Bowley, Milagros Alvarez Imaz, and Paola Salio

.1 simulation using boundary conditions from the ECMWF fifth-generation atmospheric reanalysis (ERA5) ( Copernicus Climate Change Service 2019 ). The ERA5 is an hourly reanalysis dataset with 0.25° horizontal resolution and 37 vertical layers from 1000 to 1 hPa. Here, the simulation primarily is used to downscale the reanalysis boundary conditions with better-resolved topography and to examine the storm and the rapidly evolving environment leading up to it. The WRF simulation outer domain, covering much of

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