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cipitation and temperature during a water year and conversion to "depend- able" streamflows, It is possible, through the use of this method, to pro- duce a firm estimate of seasonal dependable inflows, either for a single river basin or a complex of river basins, without any reference to the critical water year. It permits the discernment of low water and high water years heretofore unrecorded in the historical data. Much of the basic research necessary in adapting the method to streamflow forecasts has been supported by private power interests in the Pacific Northwest. To date, commercial tests have been concerned pri- marily with river basins in that region. Therefore, this paper must limit a review of results to the Columbia River and its tributaries. However, the experience gained here, as well as the basic principles underlying the work, permit adaptation to streamflow forecasting in any region where adequate historical hydrometeorological data are available. An assessment of the 1957-58 water year forecasts, prepared for the Lewis River at Merwin Lake in Washington, and for the total inflow at Grand Coulee in Washington, will be reviewed. These forecasts were pre- pared during the course of the spring and summer, and issued in September 1957. Importance of streamflow estimates is greatest during the fall months. Storage may be drawn down at that time with confidence in a year such as 1957-58, when the characteristics of the streamflow projections for the winter months depart radically from the 1936-37 year. This is exemplified in the verification of the monthly flows at Grand Coulee and Merwin Lake, where decreasing flow in relation to usual median flow trends, as projected for November, was followed by a sharp upturn by February. The actual flows confirm this pattern. The forecast scheme mentioned above, utilizing antecedent conditions as a starting point for a streamflow projection with the 1936-37 characteristics for succeeding months, would not indicate on December 1 the upturn in January and Feb- ruary, but a decided decrease in flows during those months. The continual refinement and extension of the method of streamflow forecasting described in this paper can provide for a firm estimate of dependable flows because it does not depend upon the use of statistical relationships which have no physi- cal basis. Important benefits not now obtainable would accrue to the interest of power, flood control, irrigation, navigation, and other conservation uses. Some of the benefits that would be realized by the three primary interests are: Power - Greater amounts of secondary energy could be sold by the Federal Government and non-federal utilities. Expensive steam generation by private utilities would be minimized and - 15 -