What Is the UV Index and How It Came About

As a guide to provide important information to help you plan your outdoor activities, in the hopes of preventing overexposure to the sun, AccuWeather developed an UV index in the early 1990s. AccuWeather meteorologists were part of a UV Stakeholders’ group convened by the Environmental Protection Agency (EPA) to plan for the National Weather Service (NWS) index. the National Weather Service and the Environmental Protection Agency developed the Ultraviolet index, for the United States.

It's reported that the first UV index was created by the Canadians in 1992. Other countries later followed suit with their own indices. However, the methods of calculating and reporting a UV index varied across the globe. In order to replace the inconsistencies found with forecasting the UV index, a worldwide UV index was later developed, and today it's standardized by the World Health Organization.

The sun's rays are known to be harmful; they emit ultraviolet or UV rays that are transmitted in three different wavelengths, which are dangerous to the skin. Overexposure to these rays can lead to skin cancer. The UV index is a vital tool citizens can use to limit their chances of being diagnosed with skin cancer or other skin-related illnesses.

Here’s how it works. The UV index is a daily forecast of the expected risk of overexposure to the sun. It predicts ultraviolet intensity levels on a scale of 0 to 10+, where 0 indicates a minimal risk of overexposure and anything 10 and over means a very high to extreme risk. If your forecast calls for a level 10 on the UV index for a particular day, you should limit outdoor activity. If outdoors between the hours of 10 a.m. and 4 p.m. you could develop sunburn in less than 15 minutes.

While the NWS UV index is very limited (only available for major cities, updated once per day, tomorrow’s high value only), AccuWeather’s is extremely comprehensive – every location on earth, current value and hourly values for each of the next 25 days, updated at least hourly.

For more on the UV index for your area, check out AccuWeather.com's ultraviolet radiation page. Just enter your city at the top of the page.

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