The UV Index number, ranging from 0 to 10+, indicates the amount of UV radiation reaching the Earth's surface during an hour around noon. If you are in an area where the level is 5 or higher, be extra vigilant. The rating is only valid for about a 30-mile radius from the city, and, as with any forecast, local variability in cloud cover and other factors may change actual levels experienced. The following Web sites provide updated UV Index ratings, as the numbers do fluctuate:;