Precipitation evaluation of the North Dakota Cloud Modification Project (NDCMP) using rain gauge observations

The North Dakota Cloud Modification Project (NDCMP) is a state-managed, cost-sharing weather modification program with a primary goal of reducing crop hail damage and a secondary goal of increasing precipitation. North Dakota has conducted NDCMP in western North Dakota since 1976. This analysis evaluates the 1977-2018 cloud seeding impact on rain gauge measured precipitation using an exploratory historical target/control statistical analysis. Three counties where seeding is conducted each year are target areas: McKenzie, Bowman, and Ward. Neighboring counties where little or no seeding occurred are control areas. Averages of available daily rain gauge measurements provide monthly and seasonal (June-August) area precipitation amounts for the target and control areas. Double ratio statistics are determined using the pre-NDCMP period of 1950-1975 and the NDCMP period of 1977-2018. The statistics use the McKenzie and Bowman target areas paired with four different control areas, along with the Ward target area paired with one control area. Six of eight McKenzie and Bowman target/control pairs have double ratios (1.01-1.12) possibly indicating higher target area precipitation during NDCMP. Additionally, two of eight ratios have a 95% statistical chance of being greater than 1.0. The Ward target/control comparison indicates no enhancement. The average of all nine target/control ratios is 1.03, consistent with a modest overall precipitation enhancement by NDCMP hail suppression operations.