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<br />.SOME CLIMATOLOGICAL CHARACTERISTICS OF SEEDABLE <br />UPSLOPE CLOUD SYSTEMS IN THE HIGH PLAINS <br /> <br />C. D. Whiteman <br /> <br />A model. of seeding opportunity recognition is developed <br />for shallow wintertime cloud systems in the High Plains of the <br />United States. The model uses, rawinsonde network data for <br />the High Plains to determine climatological characteristics <br />of "seedable" upslope cloud systems. Included are annual, <br />monthly, and diurnal frequencies of occurrence of seedable <br />cloud systems as well as characteristics of the cloud systems <br />themselves. Such characteristics include cloud thicknesses, <br />heights of cloud tops and bases, lapse rates, cloud top <br />temperatures, upslope wind components, and the relative <br />frequencies of precipitating and nonprecipitating cloud <br />systems. <br /> <br />1. INTRODUCTION <br /> <br />In the winter season, upslope wind conditions occur frequently in <br /> <br />the High Plains region of the United States. These conditions move <br />moisture-laden air up the slope of the High Plains towards the foot- <br />hills of the Rocky Mountains. The expansion and consequent cooling of <br /> <br />the ascending air may result in condensation and generation of wide- <br /> <br />spread decks of stratus or stratocumulus clouds. <br />Two processes (Fletcher, 1962) may be effective in generating <br />precipitation from these orographic cloud systems: <br />1. The collision and coalescence of cloud droplets, and <br />2. The Bergeron-Findeisen process. <br />The first process may occur in any cloud containing sufficiently <br />large liquid droplets, while the second process requires the presence <br />of ice crystals within a cloud containing supercooled water droplets. <br />