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severe cases. the single convective cell can extend from near sea level to the tropopause, a vertical distance of 8 to 14 kilometers. depending on latitude and season. The horizontal diameter of such cells is limi- ted to 2 or 3 times the vertical diMension. so it can be seen that the areal extent of local-storm cells ranges from a few square kilometers up to about 1.000 square kilometers. Rapid overturning of the air mass accompanied by a strong convergence of the falling rain can result in extremely high intensities of rainfall over an area much smaller than the total extent of the convective cell. IIhen the air mass is completely overturned, it becomes relatively stable, and precipitation essentially ends. This usually takes 2 or 3 hours. Both general and local storms move during the course of their life. Thus, the pattern of storm-total precipitation does not necessarily reflect the patterns of precipitation at various instants during the storm's life time. ^lso. convective activity is often associated with general-storm activity, and thus the irregularity of the space-time patterns of general storms can be extreme. However, heavy precipitation over large areas for sustained durations requires high winds. The high wind shear accompanying high winds usually effectively inhibits the vertical development of convective cells. Thus, precipitation is some- what uniform in time and area during large cyclonic and orographic storms (except for topographic effects discussed below), although con- vective precipitation often follows in the wake of a general storm. These generalizations are based on experience in the northern hemi- sphere and particularly in the United States, but are believed to apply generally throughout the world. Section 2.Q3. Geographic variations of storm potential Storm potential at any specific location is a function of (a) the distance from sources of moisture and the characteristics of intervening 2-03