Water Supply Forecasts - What they represent.

Water supply in the West depends greatly on snowmelt. Water Supply Forecasts issued by the River Forecast Centers represent the volume of water that is expected from snowmelt at a given location over a given period (usually the runoff period). For example, a forecast may be for 7.3 million acre feet from April 1-July 31 at Lake Powell. This value is then compared to the average volume at that location over the same period of time, and that would be what is displayed on the map.

Water in the West is very often regulated by being rerouted through tunnels and ditches, diverted onto croplands and into treatment plants, and temporarily impounded in reservoirs many times along the way. Water Supply Forecasts are most often unregulated, meaning they represent the volume of water expected to flow through a location over the runoff months as if there were no regulations or diversions. Unregulated forecasts do not represent what will be observed in the stream unless no upstream regulation takes place.

Water Supply Forecasts are used by reservoir managers to plan how best to operated the reservoirs to meet demands on the system, and by anyone interested in water resources who needs to know how much water will be available during the current water year.

To learn more about water supply forecasts, and how they are developed, you may visit the following websites:

Colorado Basin River Forecast Center
Northwest River Forecast Center