Outdoor misting fans work best in dry and arid environments, like the desert. In areas with less than 40 percent humidity, ambient air temperatures can feel up to 30 degrees Fahrenheit cooler. In an area with average relative humidity (40 and 80 percent), air temperatures can feel about 20 degrees Fahrenheit cooler. In high humidity (more than 80 percent), the cooling effect is about 10 degrees Fahrenheit.