On 25 April 1975, as part of the National Aeronautics and Space Administration's Atmospheric Variability Experiment IV, frequent upper-air soundings were taken at eastern United States synoptic sounding sites. An intense, long-lived mesoscale convective weather system developed late in the AVE IV period and moved eastward during the remainder of the experiment. With the use of dry and moist numerical simulations, performed with Drexel University's Limited Area and Mesoscale Prediction System (LAMPS), interaction between the widespread, long-lived convective complex and its large-scale environment are examined.
Dissecting the differences between moist and dry simulations reveals that, within the moist numerical simulation, significant up-scale feedbacks occur between the convective system and its large-scale meteorological setting. Pronounced differences in temperature, divergence, vorticity, and height develop between the two simulations. Physical reasons for these differences are discussed. Comparison of the model forecast with analyses of the actual evolution of large-scale features indicates that this type of weather event cannot be properly simulated without inclusion of the effects of the latent-heat driven, mesoscale convective system.