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<br />Ht <br />(km) <br /> <br />5 - <br /> <br />SEEDABLE LAYER CRITERIA <br /> <br />1. Moist layer has relative humidity ~ 85% <br /> <br />2. Cloud base < IOOOm AGL <br /> <br />3. Cloud thickness> IOOOm <br /> <br />4. Cloud top -15s T s -50C <br /> <br />5. Top of moist layer has either <br /> <br />a. an increase in temperature <br />lapse rate to isothermal or <br />more stable than Isothermal <br />or <br />b. a rapid decrease In <br />relative humidity <br /> <br />4 - <br /> <br /> <br />Figure 1: Model. ariteria for <br />reaogni tion of a seeding o~- <br />portunity from pl.otted raW~n- <br />sonde data. <br /> <br />3 <br /> <br />2 <br /> <br />o <br /> <br />-15 -10 -5 0 TEMP. (OC) <br /> <br />Super et al. (1971) discussed the determination of cloud <br />base from rawinsonde data and presented the results of 23 <br />rawinsonde observations of typical winter clouds studied <br />during February 1970; they concluded that the mean relative <br />humidity at cloud base was 84.8 percent and the standard <br />deviation was 9.2 percent. The extremes were 100 and 63 <br /> <br />percent. <br /> <br />2. A moist layer base within 1 km of the ground. Shallow cloud <br />systems with bases higher than 1 km are assumed to have <br /> <br />~, <br /> <br />little potential for artificial precipitation because 'of <br />the possibility of increased evappration and sublimation of <br />hydrometers into unsaturated air. <br /> <br />4 <br />