Basin-scale internal waves are examined using a combined field observation and 3-D numerical approach. The field site, Lake Tahoe (CA-NV) during winter, is characterized by the presence of a weak density stratification and the passage of several storm fronts of varying character. Under these conditions internal waves with periods greater than 5 days and displacements of 30 m are possible. The model used is shown to have negligible numerical dissipation and sufficiently small phase lag over the time periods needed to represent basin-scale waves. Both the numerical results and the observations identify the presence of three Kelvin modes and one Poincar¿ mode. While the wave periods are consistent with theoretical predictions, the spatial characteristics are far more complex than theory can predict. The spatial features are revealed through analysis of the integrated potential and kinetic energy fields yielded by the model. This shows that the basin topography exerts an influence on both Kelvin and Poincar¿ waves. The effect of the variable storms and, in particular, the phasing of the storms with respect to the internal waves is shown to be responsible for the amplification and annihilation of the basin-scale waves.