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Another High UV Index Friday; here's how UV's calculated

Several different factors determine how high the UV Index can be.

AUSTIN, Texas — A high UV index mean's that there's a greater risk for sunburn, amongst other skin-related ailments, such as melanoma (skin cancer).

But here at KVUE, we wondered, how is the UV index calculated?

Well, here's your answer!

According to the Environmental Protection Agency, the National Weather Service (NWS) uses a computer model that combines ground-level solar UV radiation with the ozone concentration in the stratosphere, as well as cloud cover and ground elevation.

Credit: KVUE

Each factor has a certain function when it comes to UV rays. The ozone layer - usually in the stratosphere but can have particles near the surface, especially in urban areas with stagnant air - largely prevents the strongest UV rays from reaching the surface. Cloud cover has a similar function, but more of those UV rays are limited by cloud cover than by the ozone layer. This is due to the water molecules in clouds absorbing the UV light as opposed to reflecting them in different directions. Thicker clouds absorb more of the UV light due to their density, thus limiting the UV light at the surface.

However, ground elevation works differently. The higher the elevation, the higher the UV rays will likely be. Thus, places like Denver (elevation 5,276 feet) and Mexico City (elevation 7,349 feet) will have far higher UV indices than here in Austin (elevation 489 feet), as Denver and Mexico City will have thinner atmospheric layers, and thus, more UV light will be able to reach the surface.

With all of this in mind, the NWS's calculation of the UV index for Friday sat at a 12, which placed it in the extreme category. This is also forecast for Saturday, so if you have any outdoor Father's Day Weekend plans, be sure to apply and reapply the sunscreen every two hours to prevent sunburn.

Credit: KVUE

Stick with KVUE for more on skin protection during this serious heat wave.

In the meantime, your seven-day outlook is below.

Credit: KVUE

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