These 3 images show afternoon white clouds over all of the major Tharsis volcanoes. The first two were imaged a day apart while the 3rd was about one month later. During this period, clouds formed almost daily over volcanoes. Note the dust clouds over the Southern perimeter of the North Polar Cap in the first two images. Winds that develop with the sublimation of ice drive the dust clouds and also produce the dark collar that surrounds the NPC. Also note the dramatic decrease in the size of the NPC in the third image. A cloud appears over Olympus Mons, the largest volcano on Mars near the center of each image.