This paper focuses on the evaluation of the North Dakota Cloud Modification Project (NDCMP). The goal of the research is to study the effects of cloud seeding on precipitation generation in the target and downwind regions of the two cloud seeding districts in Western North Dakota. The Atmospheric Resource Board Cooperative Observer Network (ARBCON) rain gauge data were used for the study. Rain gauge data are categorized into target, downwind, and control regions. The target region includes gauges in each district and the downwind region includes gauges downwind of each district. Rain gauges adjacent to the target region were used as the control. Precipitation was evaluated on a monthly basis. The downwind/control regions for each month were determined by looking at TITAN storm tracks from 1999 to 2002. Regions were determined based on predominant wind flow regimes. Two main wind flow regimes, Northwest and Southwest flow, were used in this study. The flow regimes were based on the NCEP/NCAR Reanalysis wind data.

Results from the analysis of 27 years of NDCMP data indicate that seeding has a positive effect on increasing precipitation amounts in both the target and downwind regions. Preliminary results show average precipitation amounts increased by 6-9%. A description of the methodology and detailed results will be shown in the presentation.