Frequently Asked Questions about the Weather Want to learn more about specific products that AccuWeather offers? Use the links below for general information, and the tabs above for more extensive sections. Select a question: ------------------ How does Wind Chill work? Why do the leaves change color in the fall? What is the Fujita Scale for Tornadoes? Why is the sky blue? What Are CDD, HDD, and GDD? What are Humidity, Dewpoint, and Wetbulb?