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<br />D R AFT <br /> <br />~ <br /> <br />SECTION VI - WINTER OROGRAPHIC PRECIPITATION <br />MANAGEMENT - IDENTIFICATION OF IMMEDIATE <br />QUESTIONS TO BE ANSWERED <br /> <br />A. .opportunity Recognition <br /> <br />Recognition of the opportunity to increase precipitation in winter <br />orographic clouds is the single most difficult problem to be faced in <br />the transition from experimental to operational weather modification <br />in the Colorado River Basin. Seedable periods will have to be <br />forecast enough in advance or conditions recognized rapidly enough <br />during a storm to allow for efficient treatment of the systems. <br /> <br />Prior to the CRBPP, weather modification research experiments treated <br />eve~y storm condition and later stratified the data to determine <br />those conditions most suitable for precipitation enhancement. The <br />CRBPP was the first experiment to attempt to recognize the seedable <br />opportunity by warm cloud tops up to 24 hours in advance. Two indices of <br />opportunity were used: one was a range of 500-mb temperatures and <br />the other was a range of rawinsonde-derived cloud top temperature. <br />Although anticipated to be a relatively simple procedure, both <br />indices proved to be variable and difficult to forecast. <br /> <br />~ <br /> <br />All previous experiments and the CRBPP have proven that cloud condi- <br />tions exist where seeding can increase as well as decrease precip- <br />itation in the basin. Analyses have been conducted to identify <br /> <br />51 <br />