WMOD00274 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I Two cloud types produce all precipitation: "warm clouds" and "cold clouds." A "warm" cloud is one in which the entire cloud volume is at a temperature warmer than freezing and unable to produce ice crystals as a result. The convective warm cloud is characterized most often by relatively slow growth. Warm cloud water droplets eventually may grow to a sufficient size and weight to fall out of the cloud if given enough time. Falling cloud droplets grow larger by scavenging other cloud droplets along their downward paths. Although this type of cloud appears in Western Kansas, it's not the dominant type of cloud producing precipitation here. Interestingly, if warm clouds grow to sufficient heights and transition into cold clouds, the large- sized, warm-rain drops can be important embryo sources in the production of hail when carried aloft rapidly by updrafts into sub-freezing cold cloud environment where eventually they freeze and grow quickly into large hail. While seeding, pilots often find rain falling into below-cloud base updrafts. However, most important to Western Kansas is the "cold" cloud. Cold clouds tend to be much taller and have more volume than warm clouds, so there is a greater amount of moisture available to the precipitation process developing within the cloud. Cold clouds have a portion of their volume that has risen high enough to have passed into below-freezing atmospheric temperatures. When such clouds form, the interaction between the super cooled water drops and ice crystals within the cloud initiates the process responsible for producing the most significant precipitation in Western Kansas and does so in a relatively short time span compared to warm clouds. Cold clouds are typically the main culprit for heavy flooding rains over a short period of time. The widely-accepted hypothesis under which the WKWMP hail suppression operates is called "beneficial competition." Most, if not all, credible long-term hail suppression programs assume beneficial competition is needed to solve the hail problem. As mentioned earlier, hailstones grow to large sizes in thunderstorms due to the lack of sufficient numbers of IN particles within the cold cloud while it is growing. This natural insufficiency of IN particles allows relatively abundant supercooled water droplets to collect upon the relatively few numbers of ice crystals causing hail to grow to large sizes. Too often those ice particles grow into hailstones so large they can't melt before reaching the earth's surface. By vastly increasing the concentration of ice crystals within these ice crystal-deficient clouds, competition for available cloud water increases to the point that hailstones are prevented from attaining sizes large enough to damage crops and property under most circumstances. Hail growth and movement within storms, especially very severe ones, can be very complex. In very strong storms hail may be cast miles away from the storm itself. Hail damage is determined by many factors: the type of crop and the stage of growth the crop was in, the hail size affecting the crop and whether or not it was wind-driven are all important considerations. Those same general factors also apply to any property damaged by hail (i.e. resilience to hail, size of hail, etc.). The seeding agents used on the WKWMP Program are delivered to clouds by aircraft. Both liquid and solid (flares) complexes of silver iodide (AgI) are used as our cloud base seeding agents of choice. They are vaporized in updrafts at cloud base to produce ice nuclei rising into clouds through the natural action of the cloud's own updraft. ArIother seeding agent, dry ice, is dropped directly into growing clouds at altitudes above freezing up to -1 OC while flying through the growing cloud towers feeding the main storm updraft. These "feeder" clouds quickly merge 5