How bad are the dust storms on Mars?

Mars is famous for its large, planet-wide dust storms. Mars has an atmosphere which is much thinner than the atmosphere on Earth, but which still creates winds. When these winds pick up the fine, dry particles of dust on Mars, a dust storm can occur. Most dust storms cover an area for a few days and carry small particles of dust at speeds of 33 to 66 miles per hour. Sometimes, though rarely, dust storms on Mars can be fierce enough to cover the entire planet in a dusty haze for weeks.