The primary source of water for much of the semi-arid western U.S. is snow stored in mountain basins. Monitoring the snow water equivalent (SWE) is critical in water resource management. There are currently no methods to accurately measure SWE over large lateral distances. Ground-penetrating radar (GPR) is a tool that can potentially provide laterally continuous measurements. Previous studies have shown that measurements of GPR velocity can provide accurate estimates of SWE in dry snow. However, introduction of liquid water into the snowpack results in a 3-phase system that cannot be accurately characterized with GPR velocity alone. Measuring the frequency dependence of GPR signal attenuation provides a direct estimate of the complex dielectric permittivity. This additional parameter allows measurement of liquid water content, snow density, and SWE. At two field sites, the new method provided SWE estimates, accurate to within 11% or less, in both wet and dry snowpacks.