85th AMS Annual Meeting

Monday, 10 January 2005
Evaluation of Hail Suppression Operations on the North Dakota Cloud Modification Project 1985-2003
Aaron Gilstad, North Dakota Atmospheric Resource Board, Bismarck, ND
The concept of beneficial competition, whereby seeding of a cloud results in an increased number of hail embryos which compete for limited super-cooled liquid water in the cloud, is one of the primary methodologies for hail suppression operations. The efficacy of the North Dakota Cloud Modification Project (NDCMP) with regard to its primary goal of hail suppression continues to be a subject of study. An evaluation of observed hail reports from the Atmospheric Resource Board Cooperative Observer Network (ARBCON) shows a shift to smaller, less damaging hail in seeded areas versus adjacent control areas. A comparison of the percentage of hail of a given size range that falls in District 2 of the NDCMP versus the remaining non-project western counties for 1994-2003, for instance, showed that hail in the seeded area was seven percent lower for hail with a diameter between 0.75 and 1.50 inches, two percent lower for hail between 0.5 and 0.75 inches diameter, and eight percent higher in hail less than 0.50 inches diameter. Although one cannot measure what did not fall, one can, with a sufficiently dense observing network, see a hail spectrum shift from larger to smaller.

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