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<br />174 <br /> <br />after seeding but some minutes later while preparing to <br /> <br />return to the airport, he noticed a ring-shaped shadow <br /> <br />on the ground some distance away from where he had seeded. <br /> <br />He could even then barely see the cloud itself. <br /> <br />Forecasting Proper Conditions <br /> <br /> <br />The second major aim of the program was to refine <br /> <br /> <br />forecasting techniques. Working to the lee of the Rockies, <br /> <br /> <br />with the occurrence of wave activity quite frequently <br /> <br />ahead of short waves advancing through the long wave jet <br /> <br />pattern, proved to be a boon with regard to forecasting. <br /> <br /> <br />Almost every wave was preceded oy more or less high-level <br /> <br /> <br />moistu~e that, if there were waves, almost always resulted <br /> <br /> <br />in at least some areas becoming ice-supersaturated. This <br /> <br /> <br />gave us a great frequency of opportunities to seed. How- <br /> <br /> <br />ever, air flows through th~se standing wave patterns and <br /> <br /> <br />so long cloud life-times W~re not possible. <br /> <br /> <br />Other helpful signals for forecasting a high proba- <br /> <br /> <br />bility of ice-supersaturat~d conditions overhead were found. <br /> <br /> <br />Vertical velocity calculations performed from the observed <br /> <br /> <br />turning of the winds with height over a single radiosonde <br /> <br /> <br />station showed upward motion more than 70% of the time when <br /> <br /> <br />high clouds or persistent contrails were observed in the <br /> <br /> <br />region. Extrapolation of the forecast 700 mb humidities <br /> <br /> <br />from the National Meteorological Center's LFM numerical <br /> <br /> <br />model downwind and upward proved to be a useful procedure <br /> <br /> <br />when applied in the proper synoptic situation. Extra- <br />