The Mars Orbiter Laser Altimeter detected clouds during the polar night on Mars. While these clouds are associated with topographic features, and are clearly mountain wave clouds as suggest by Pettengill and Ford <2000>, we suggest that they differ greatly from terrestrial mountain wave clouds. Uplift generated from flow over the mountains may initiate the clouds on both planets. Terrestrial wave clouds are generally compact features with sharp edges. However, we find that the relatively large mass of condensate on Mars leads to diffuse clouds with snow tails that may extend many kilometers downwind from the mountain and even reach the surface. Both the observations and the simulations suggest substantial carbon dioxide snow precipitation in association with the underlying topography. This precipitation deposits CO2, dust, and water ice to the surface and may lead to propagating geologic features in the Martian polar regions.