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I I I I I I I I I I, I I I I I ) I A "warm" cloud, is one in which its temperature is not below freezing and does not produce ice crystals in its volume. This cloud is generally characterized by a relatively slow growth of cloud water droplets which eventually may grow to su'fficient size and weight to fall from the cloud. While falling, cloud droplets collect other cloud droplets by scavenging them along their downward paths. Although this type of cloud occasionally appears in Western Kansas, it doesn't have a dominant role in producing precipitation here. However, large size warm-rain drops can be important embryo sources in the production of hail when they merge ,into sub-freezing clouds that are not of the warm-rain variety'cloud and get carried aloft rapidly by updrafts where they freeze and can grow into large hail. Most important to Western Kansas is the "cold" cloud. Cold clouds have a portion of their volume reaching temperatures below freezing. It is the interaction between its supercooled water drops and ice crystals which initiates and promotes the process most responsible for producing significant precipitation here. The prevailing hypothesis under which the WKWM Program hail suppression portion operates is that hailstones grow to large sizes because there are too few ice crystals formed naturally in clouds during vigorous thunderstorm growth, thereby allowing relatively abundant supercooled cloud water to collect upon relatively fewer numbers of ice particles or other hail embryos. Too often those particles grow into hailstones too large to melt before impacting the earth's surface. Current theory is that by vastly increasing ice crystal concentration within these ice crystal-deficient clouds, hailstones will be prevented from growing to a size large enough to damage crops and property through strong competition for the available cloud water. Property type, crop type, stage of crop growth and hail size are all important factors in determining damage severity. ' Research has found that hail growth and movement within storms, especially very severe ones, can be very complex. However, most long-term hail suppression programs use the same hypotheses and seed clouds in much the same way we do in Western Kansas. In 1994 the Kansas Water Office performed the most recent evaluation of the WKWMP and found a 27% reduction of crop-hail damage which was statistically significant at the 5% level. The hail suppression seeding agents used on the WKWM Program are either silver iodide-based or dry ice and employ aircraft to 'deliver the agents to the clouds. Silver iodide ice nuclei are vaporized in updrafts at cloud base, whereas, dry ice is dropped directly into growing cloud updrafts at temperature levels of -lOC, around 20,000 feet in mid-summer. Experimental hygroscopic flares were tested this summer, these were composed of sodium iodide, potassium iodide and lithium chloride. Unlike silver iodide, hygroscopic particles work in warmer-than-freezing cloud temperatures to enhance rainfall. 5