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<br />1. Introduction <br /> <br />Experiments to develop the technology for sci~ntific precipitation management <br />of summer convective clouds on the High Plains require background information <br />which describes the natural variability of convective clouds and the thermo- <br />dynamic controls of natural moist convection. Conditions favorable for <br />convective cloud development have been summarized in the Thunderstorm Project <br />(Byers and Braha-n, 1949) and by Newton (1963). These convective controls <br />include conditional and convective instability, moisture in the lower tropo- <br />sphere, surface heating to the condensation level, and mesosynoptic forcing <br />functions. <br /> <br />House (1963) demonstrated the importance of dynamic mechanisms which lift the <br />atmosphere resulting in release of instability. Mesoscale triggering effects <br />generated by dissipating thunderstorms which initiate new cells have been <br />identified by Fujita (1963). These local mesocold fronts and co~vergence <br />lines associated with the moist downdraft of thunderstorms act as efficiEmt <br />convective triggering mechanisms when sufficient moisture and instabil ity <br />exist. In the Plains the convergence associated with the dry line is also an <br />important mesoscale triggering mechanism (Rhea, 1966; Schaefer, 1974). <br />Favorable conditions for mountain orographic convective cloud develop- <br />ment have been studied by Booker (1963). He showed that the elevated heat <br />source and the flow of air over mountain ranges may initiate and intensify <br />convective development in mountainous terrain when sufficient moisture is <br />present. <br />