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<br />I - - <br /> <br />The model does not distinguish between the seedabi1ity of a cloud <br />layer that is not producing precipitation naturally and one in which <br />precipitation has already begun. Seeding may initiate precipitation, <br />or it may affect the rate of precipitation. Thus, both conditions may <br />be seedab1e, and the amount of artificial precipitation produced will <br />depend not only on changes in the efficiency of the precipitation <br />process but also on the duration and areal extent of the seeding <br /> <br />effect. <br /> <br />Allowance is made to include some Iborder1ine" cases in the <br /> <br />climatology when most model specifications are satisfied but others <br /> <br />have departures from specifications within the accuracy of the re- <br />cording equipment. Borderline temperatures are -3 to _50C and -15. to <br />-170C, humidities from 80 to 85 percent, moist layer thicknesses from <br />800 to 1000 m, and temperature inversion, or dry layer, up to 80 rrb <br />above the moist layer. A system having moist layers separated by a thin <br />dry layer is also allowed in the analysis when the other criteria are <br />sati s fi ed. <br /> <br />I <br /> <br />, <br /> <br />The seedable layer criteria, as defined in figure 1, apply to any <br />existing cloud system in the High Plains, irrespective of the mechanism <br />by which it formed. Shallow upslope storms formed by orographic lifting <br /> <br />of moist air will, therefore, not be differentiated from areas of deep <br /> <br />fog, or fog that has been lifted to form shallow stratus decks. The <br />addition of a criterion for upslope wind conditions (i.e., an upslope <br />wind component in the sounding somewhere from the surface to 700 mb) <br /> <br />7 <br />