This study uses remotely sensed long-term (1966--1999) weekly snow cover extent data to investigate snowmelt runoff response to seasonal snow cover change in the large Siberian watersheds (Ob, Yenisei, and Lena basins). It quantified the seasonal cycles and variations of snow cover extent and river streamflow and identified a clear correspondence of river streamflow to seasonal snow cover extent change; i.e., an association of low streamflow with high snow cover extent during the cold season and an increase in discharge associated with a decrease of snow cover extent during the melt periods. This study also examined and compared the weekly mean streamflow with the weekly basin snow cover extent for the study period. The results revealed a very strong linkage between the streamflow and snow cover extent change during the spring melt season over the large Siberian watersheds and developed a statistically significant weekly runoff-snow cover relation. This relation suggests a practical procedure of using remotely sensed snow cover information for snowmelt runoff forecasting over the large northern watersheds. Analyses of extreme (high/low) streamflow cases (years) and the associated snow cover conditions indicate an association of high (low) flood peak with late (early) snowmelt in the Ob and Yenisei basins. Comparisons of snowmelt timing with peak flow show different associations between these two variables among the large Siberian rivers. These results demonstrate that the NOAA weekly snow cover extent data are useful for understanding and predicting streamflow changes in the Arctic regions. Snow cover water equivalent data/products obtained by remote sensing technology and in situ snow observations are currently being examined for what we expect will eventually improve hydrologic forecasts over the large northern watersheds.