Radiant sky hemispheric temperature, snow-surface temperature, and thermal profiles within the snowpack were measured at night in a frost hollow in southeastern Michigan, U.S.A. Snow-surface temperatures remained 3° to 5°C colder than air temperatures at 3 m above the snow surface and 6° to 7°C colder than air temperatures at 18 m, the height of the hollow's rim above its floor. Due to suppression of turbulent heat transfer, the energy balance at the surface was dominated by net longwave radiation; energy involved in sensible heat transfer through the snow was equal to only about 10% of the incoming longwave radiation. Incoming longwave radiation can be expressed as a linear function of surface temperature by means of a regression equation, which yields a coefficient of determination of 0.75.