In mountainous regions, runoff from snowmelt is an important hydrologic and economic factor, and therefore early runoff forecasting brings significant advantages to the planning and operation of water resources systems. Similarly, predicting runoff from snowmelt during spring months in the eastern part of Turkey, where most of the water originates from high mountains and contributes to the large dams on the Euphrates River, is of crucial importance. In this study, an event-type, physically based hydrologic model Hydrologic Engineering Center (HEC-1) interfaced within the program Watershed Modeling System is applied to the Upper Karasu Basin to simulate rainfall-snowmelt hydrographs during 3 years. The model relates snowmelt to temperature using the degree-day factor, a common practice in the simulation of snowmelt. The model accounts for growth and depletion of the snowpack in terms of snow water equivalent, which is tracked in each of the elevation zones into which the basin is divided. The ground-truth data for snow are coupled with the snow depletion curves obtained from satellite data (NOAA-AVHRR) to determine snow water equivalent values at the beginning of each event.