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Peter Knippertz and Andreas H. Fink

-averaged anomaly of −23%. These results suggest difficulties of the ECMWF model in triggering convection in cases with an anomalous moisture inflow into the study region prior to day 0 but without a direct synoptic forcing by an upper-level trough as for the hits. The possible influence of a misforecasted synoptic setting is addressed in section 6c . The composite analysis for the false alarm cases reveals very large anomalies in Z500, MSLP, and TD2M ( Fig. 12g ). Note, however, that the strength of the

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Dawn L. Sanderson, Edward D. White, Andrew J. Geyer, William P. Roeder, and Alex J. Gutman

1. Introduction Lightning is one of the most powerful and frequent natural phenomena that poses a risk to everyday life. Particularly concerning to the safety of human life, equipment, and machines is the appearance of cloud-to-ground (CG) lightning ( Rakov 2016 ). Due to the severe danger lightning presents for both personnel and equipment, the Air Force (AF) and its civilian counterparts conducted extensive research to ascertain the ideal balance between safety and productivity. Located on

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Adam J. French and Matthew D. Parker

. Bluestein and Jain (1985) observed both supercells and backbuilding squall lines forming in similar environments, and in similar proximity to surface boundaries. They hypothesized that the orientation of the vertical shear with respect to the boundary may have been relevant to the convective mode. To this end, Bluestein and Weisman (2000) examined the effects of varying the wind shear angle with respect to a line of forcing (in their case a dryline) on numerically simulated supercells. In their

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

second partitioning method in Milrad et al. (2010) revolved around three commonly used quasigeostrophic (QG) ascent-forcing variables: low-tropospheric horizontal temperature advection, midtropospheric vorticity advection, and low-tropospheric frontogenesis. Two event types were established—cyclone and frontal. The composite features in the cyclone group exhibited a strong sea level cyclone originating in the Gulf of Mexico. In contrast, the frontal group composite displayed a relatively benign

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Peter M. Caplan and Glenn H. White

systems(White 1988b). This problem is reduced in the newmodel.3. Medium-range forecast model performance during Northern Hemisphere summer In summer, mean errors in the MRF appear to berelated to thermal forcing. At 1000 mb (Fig. 9) theheight forecasts for June-August 1988 display positivebiases over the northern oceans and negative biasesover the land masses where thermally induced lows areoverforecast. At 500 mb (Fig. 10) the forecasts maintain the analyzed pattern of the time-mean troughs

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Jerilyn M. Billings and Matthew D. Parker

remain cold pool driven and surface based during the nighttime hours. The squall line in this study continued to move in the direction of its surface-based cold pool even after the boundary layer was stabilized, suggesting that it may be one such example. It has also long been known that a dynamically induced perturbation vertical pressure gradient force in supercells can lift environmental air even when its buoyancy is small or negative ( Rotunno and Klemp 1982 , 1985 ; Weisman and Klemp 1984

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Fang-Ching Chien, Ying-Hwa Kuo, and Ming-Jen Yang

between 12 and 24 h, during which the 1200 UTC runs had difficulty in predicting the daytime precipitation. Because daytime rainfall during this season was usually associated with diurnal thermal forcing and orographic lifting, this might indicate deficiencies in the parameterization of convective triggering in the cumulus parameterization scheme. Additional studies need to be performed to investigate whether improvement of grid resolution, improvement in convective triggering parameterization, and

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James Wallmann, Rhett Milne, Christopher Smallcomb, and Matthew Mehle

often found downstream of the strongest positive pressure advection. More detailed descriptions of the dynamic tropopause and its utilization to forecast warm season convection can be found in Hirschberg and Fritsch (1991) and WA04 , respectively. At 0600 UTC 12 August 2001, an upper-level front is located over central Nevada with the main short wave and strongest positive pressure advection along the northern California coast and moving northeast ( Fig. 2a ). The area of strongest forcing is

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Gail Bayler and Howard Lewit

Fleet Numerical Oceanography Center, two computer models, the Navy Operational Global AtmosphericPrediction System, NOGAPS, and the Navy Operational Regional Atmospheric Prediction System, NORAPS,generate a twice-daily suite of atmospheric analyses and forecasts. NOGAPS is the driving force behind manyof the center's products and has become a complex, highly structured system designed to run automatically.The execution of NOGAPS and NORAPS within the operational schedule is described. The systems

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Paul J. Croft, Russell L. Pfost, Jeffrey M. Medlin, and G. Alan Johnson

, they can allow mesoscale fog predictions to be made. To achieve this, a framework for a simple operational conceptual model approach to local and regional fog forecasting, similar to that by Leipper (1995) , is presented for the southern region of the United States (gulf coast states). The conceptual model is based on macroscale forcing and moisture availability (or saturation), the character of the boundary layer, a qualitative assessment of the significance of fog microphysics (according to

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