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<br />~ <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />New-growth clouds initially are produced around severe storms mostly by below-cloud <br />base updrafts; our elevated convection-type of cloud, however, masks the difference between it <br />and the below-cloud-base cloud in that they both appear similar-looking. For pilots, the world of <br />seeding becomes greatly changed when elevated convection dominates the hail-producing process <br />in severe storms, making seeding even more hazardous, <br /> <br />This is what appears to happen most times: A storm collapses, often it is part of a line of <br />severe storms, A large gust front develops out of it, however, instead of the storm continuing to <br />collapse and die, strong new feeder clouds continue growing attached to the collapsing parent <br />storm giving the severe storm continued life. Normally, feeder clouds obtain their moisture from <br />below-cloud-base air prior to storm collapse, however, post-collapse new-growth feeder clouds <br />continue forming around the parent storm but don't exhibit below-cloud-base updrafts, yet these <br />feeders are still able to continue fueling the hail-producing process. One hypothesis is that this <br />can only happen due to some mid-level moisture convergence process, not from any updrafts <br />below cloud base, This aspect can limit the continued persistence of the parent storm, i.e" ifthere <br />is little mid-level moisture upon which to feed, the new growth clouds will continue to grow only <br />as long as there is moisture sufficient to fuel continued severe convective storm development. <br />When this moisture source is exhausted, storms no longer form, <br /> <br />Presently, it is unknown exactly what is the most important factor, or factors, determining <br />whether or not a parent storm will collapse, or whether, after a short period of re-organization, the <br />storm will resume status as a newly invigorated storm, Some of the factors determining whether <br />such a storm will persist or die appears to depend upon the storm's location relative to other <br />storms, whether or not it is in a multi-celled line, what is its direction of movement, how much <br />atmospheric instability exists, what amount of mid-level (above cloud base) moisture is present, <br />the direction, strength and organization of the winds both at mid-levels and at cloud top--there <br />are undoubtedly other factors unmentioned as welL <br /> <br />There may be times when elevated convection is unrelated to post-collapse severe storm <br />conditions such as near the end of a line of storms where strong upwind mid-level air is directly <br />impacting the cloud cluster or line of clouds. Often, the winds near, or above, cloud base are of <br />jet stream velocity helping to force convective clouds grow quickly on the upwind side and <br />become attached to the last cloud turret, even before there is cloud collapse, <br /> <br />What makes the persistent storm (growing by elevated convection) difficult to treat is that <br />after it has collapsed, no sustained, steady updrafts are found. The updrafts that are found below <br />cloud base are embedded in heavy turbulence along with equally sharp downdrafts, In fact, it is a <br />cloud seeder's "cloud from hell" seeding experience ifhe wanders into that area, At the same <br />time, above cloud base, the quickly growing feeder cells eventually produce precipitation cores <br />containing hail large enough to damage crops and property. This type of storm can only be seeded <br />effectively above cloud base where pilots report a considerable increase in turbulence inside the <br />new-growth clouds formed by the elevated convection---much greater than if penetrating non- <br />elevated clouds. Absent elevated convection, new growth cloud seeding is relatively 'benign: <br /> <br />13 <br />