Spatial-temporal variations in the extent of the seasonal snow cover of the upper reaches of the Yellow River were studied sytematically, using NOAA, Landsat, MSS and TM images, supported by ground-truth data. Effects of changing areal extent of snow cover on river flow were also examined. Spring-runoff forecasting models were developed, based on ridge regression methods and Grey theory, employing satellite snow-cover and actual hydrometeorological data to forecast inflow to the Longyang Gorge reservoir for ten-day periods between April and early June. Forecast precision is within ±15% of the actual observation. Separating snow-cover data by elevation zone improves the accuracy of forecast over lumping snow cover over the entire basin.