Would you please explain the UV index number system?
The inclusion of the Ultraviolet light index (UVI) in U.S. weather forecasts in began in the early 1990’s. Ultraviolet light, a component of sunlight, is hazardous to plants and animals and it’s very important to estimate the amount of our exposure to it. The UV index number provides that estimate. Low UVI levels are 0,1,2, moderate 3,4,5, high 6,7, very high 8,9,10 and 11 or higher extreme. Fortunately, most incoming UV is absorbed by atmospheric ozone before it reaches the Earth’s surface. Dr. Bryan Schultz, who provides the sunburn times on the Chicago Tribune weather page, informs us that the UV index for a specific location takes into account factors that decrease UV light (clouds, ozone, haze, smoke, etc.) and factors that increase it (like higher sun angle and greater altitude).