The roughness of a tundra surface, characterized by z0 shows a systematic variation throughout the spring and summer seasons. The change of 2 orders of magnitude, from 0.01 before melt to 2.8 cm in the summer, is not gradual but rather proceeds in a stepwise manner. Relatively rapid increases in z0 are shown to result form (1) rapid snowmelt, which exposes tundra tussocks and (2) subsequent growth of the vegetation canopy. The corresponding increase in turbulent mixing characterized by the drag coefficient CD, significantly affects heat fluxes over the tundra surface. Thus for heat flux modeling studies, accurate estimates of surface roughness and surface drag are esential. The time series of z0 and CD presented here should be of considerable use to modelers working in the Arctic.