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<br />~ <br /> <br />ATTACHMENT B <br /> <br />SEEDING CRITERIA <br />Established October 28. 1981 <br />Revised October, 1984 <br /> <br />The selection of suitable cloud systems for seeding operations will be based <br />on an evaluation of multiple meteorological and cloud physics parameters. It <br />1s the understanding that the follow1ng criteria w1ll be adhered to: <br /> <br />~ <br /> <br />a. <br /> <br />Cloud base water - Natural Precipitat10n. Cloud systems with a <br />cloud base water content of 1.5 gmslkgm or greater will be <br />considered as potentially seedable. In this consideration a <br />weather system will be evaluated for seeding potential if it is <br />determIned that at least natural precipitation is likely to occur. <br /> <br />b. <br /> <br />Effective temperature Pre-trough or Pre-frontal. Cloud systems <br />with cloud top temperatures of -27 degrees C or warmer will be <br />considered as potentially seedable. <br /> <br />c. <br /> <br />Effective temperature Post-trough or Post-frontal. Cloud systems <br />with cloud toP temperatures of -27 degrees C will be considered as <br />potentially seedable. <br /> <br />d. <br /> <br />8arrier level w1nds. Wind speeds from favorable directions at <br />he1ghts approx1mately 2,000 feet above the seeded barrier of 30 <br />knots or less for pre-trough cloud types and up to 40 knots or less <br />for post-trough clouds w111 be considered as potentially favorable <br />for seedIng treatment. Some adjustments are made to he acceptable <br />wind velocity ranges depending on the width of the barrier to be <br />seeded. <br /> <br />e. <br /> <br />Cloud base height. Cloud systems with bases less than 2,000 feet <br />above the mean barrier he1ght w111 be considered as potent1ally <br />seedable. <br /> <br />f. <br /> <br />Additional weather system considerat10ns. Add1tional adjustments <br />w11l be made on the seeding rate or the seeding potential of a <br />cloud system based upon the depth of the cloud system to be seeded, <br />whether the cloud system 1s 1ndicating redevelopment or is near 1ts <br />decaying stage and whether the cloud system has a potential source <br />of abundant natural nuclei from higher cloud systems. See <br />Attachment C. <br /> <br />Once a weather system 1s cons1dered seedable by evaluating the <br />above cloud and meteorolog1cal parameters, an appropr1ate seed rate <br />1s calculated for the 1nitial portion of the weather system. As <br />the forecast and observed parameters of the weather system change. <br />seed1ng rates are re-evaluated and changed as 1s necessary for the <br />new or expected cloud conditions. <br />