The coal resources of Montana, Wyoming, and North Dakota are now being developed at an increasing pace, as indicated by the present mine-mouth power plant construction, applications for land leases by utility companies, and recent increases in railroad tonnage reaching eastern and midwest utility markets. That this use of coal would continue or even accelerate was an emphatic point of the recent President's energy message. Coal development is not only necessary for the nation as a whole, but in some respects desirable for the Great Plains' economy. However, every effort should be made to minimize harmful side effects. Energy developments can adversely affect water supplies downstream and pollute the atmosphere downwind. Direct adverse effects on agriculture, animal life, and human health are now well known. The possibility that energy development by-product emissions could change downwind rainfall is not as well known but, nevertheless, real. This statement cites the evidence for such effects and describes observations now being made to determine if changes in rainfall in downwind regions (principally the Dakotas) will accompany coal developments in Montana, Wyoming, and western North Dakota. Several states in the northern Great Plains have recently conducted intentional weather modification programs designed to add as much …