Weather
Mars' temperature and circulation vary from year to year (as expected for any planet with an atmosphere). Mars lacks an ocean, a source of much inter-annual variation on earth. Mars Orbiter Camera data beginning in March 1999 and covering 2.5 Martian years shows that Martian weather tends to be more repeatable and hence more predictable than that of Earth. If an event occurs at a particular time of year in one year, the available data (sparse as it is) indicates that it is fairly likely to repeat the next year at nearly the same location give or take a week.
On September 29, 2008, the Phoenix lander took pictures of snow falling from clouds 4.5 km above its landing site near Heimdall crater. The precipitation vaporized before reaching the ground, a phenomenon called virga.
Read more about this topic: Climate Of Mars