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OOlllo8 is called "seedability." A recent definition of static seedability for increasing precipitation has been provided by the World Meteorological Organization. It states: "Clouds are considered to be 'statically seedable' for increasing precipitation if: (a) the collision-coalescence process between cloud drops is inefficient, and (b) the rate ot formation of supercooled condensate is comparable to or exceeds the rate of depletion of supercooled water, and (c) there is sufficient time to grow additional precipitation particles produced by seeding, such that they can reach the ground." Numerous studies have considered the applicability of the general hypothesis stated above; that is, to distinguish among all orographic clouds those that possess seedability and those that do not. A syn- thesis of various studies that classified storm types in Colorado indicated that while different investigators used different approaches, storms can be classified into two general types: (1) large synoptic storms that produce widespread precipitation over large areas covering mountains and valleys alike. These storms usually persist for several days as they traverse the region depositing relatively large amounts of snow in their wake. Orographic components are superimposed upon the general precipitation pattern as the storms cross the mountain bar- riers; and (2) locally produced orographic cloud systems with more local, mountain-induced precipitation. These are associated with high level disturbances and mesoscale instabilities. Snowfall is generally lighter and concentrated at higher elevations during the passage of local orographic cloud systems. Both storm types can and do occur over all parts of the Colorado River Basin. However, the northern and southern regions are generally influenced by meteorological regimes which frequently are unlinked. A higher frequency of small precipitation events associated with local orographic cloud systems occurs in the northern part of the Colorado River Basin and greater accumulations of daily precipitation associated with large synoptic storms occur more frequently in the southern part. Large synoptic storms are very complex and have much variety and gradation. Typically a large low-pressure system passing over Colorado begins with a stable cloud forming in southwesterly flow over the mountain barrier. Later it develops into a general storm transitioning from a neutral stage to an unstable stage with embedded convection. Finally the storm ends with northwesterly flow, again producing light mountain-induced precipitation as the clouds begin to dissipate. Each stage in the storm usually lasts 6 to 9 hours. The modification potential in these storms is greatest during the unstable stage which contains the greatest concentrations of liquid water and ice particle concentrations are relatively low in the high liquid water content regions associated with the embedded convection. Further, an upwind horizontal convergence zone is generally present during this stage 27 ~