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<br />Fine-mesh (-140 km) and meso-mesh (-35 km) numerical simulations <br />of a squall line showed that mesoscale vertical motion and thermal <br />advection playa key role in initiation of convective bands. Chang <br />et ale (1981) predicted vertical motion of 20 to 30 cm/s in a 100 km <br />band from 1 to 11 km MSL along the squall line of May 6, 1975. <br />Three-dimensional primative equation models using real data to <br />initialize fine-mesh models with moist physics help improve our <br />understanding of complex convergence-divergence couplets in squall <br />bands. <br /> <br />Simulations of thunderstorm evolution using a meso-8/meso-\ <br />scale three-dimensional model by Wilhelmson and Klemp (1981) show <br />how a squall line may evolve from a single convective cell in the <br />absence of imposed convergence. Here the complex transfer of mid- <br />tropospheric momentum interacted with downdraft outflow to produce <br />left- and right-moving storms. New cells developed along the outflow <br />boundary line between the "two major storms to form a line. <br /> <br />A mature supercell thunderstorm in Oklahoma was observed by <br />Dopplar radar, rawinsonde and surface observations and was simulated <br />using this three-dimensional numerical model. In their simulations, <br />Klemp, Wilhelmson and Ray (1981) found that the meso-B/meso-a scale <br />environment plays an important role in structuring many of the <br />detailed storm features. <br /> <br />Vertical and horizontal wind shear of the environmental flow <br />control, the evolution of a mesoscale cyclone, and the splitting <br />of the main updraft and location of the downdraft outflow. The <br />downdraft outflow produced a convergence zone which maintained moist <br />26 <br />