An organized signal in snowmelt runoff over the western United States

Daily-to-weekly discharge during the snowmelt season is highly correlated a mong river basins in the upper elevations of the central and southern Sierr a Nevada (Carson, Walker, Tuolumne, Merced, San Joaquin, Kings, and Kern Ri vers). In many cases, the upper Sierra Nevada watershed operates in a singl e mode (with varying catchment amplitudes). In some years, with appropriate lags, this mode extends to distant mountains. A reason for this coherence is the broad scale nature of synoptic features in atmospheric circulation w hich provide anomalous insolation and temperature forcings that span a larg e region, sometimes the entire western U.S. These correlations may fall off dramatically, however, in dry years when the snowpack is spatially patchy.