Why is the UV Index so high right now in Central Texas?

It already feels like summer in Central Texas, and with the heat and humidity comes an annual threat to your skin — sunburns.

The UV index is a measure of the ultraviolet radiation reaching the ground. That level peaks right at the summer solstice but stays very near peak for about a month before and after. That means the UV index is just about as high as it gets right now. 

The UV index is measured on a range from 1 to 11. Right now, Austin's UV index is peaking right around 10 to 10.5. That means sunburns can occur in about half an hour if sunscreen is not applied. 

Sunburns are typically thought of as a summer issue, but with the sun very high overhead, the sun's UV rays can hurt just as bad as later in the year. 

High UV levels are controlled by the thickness of the atmosphere, not the temperature. The more air the sunlight has to travel through the lower the UV levels will be. This happens because the atmosphere's ozone layer absorbs more of the UV light if the sun hits it at an angle.

In the winter, the tilt of the earth's axis means the sunlight must travel through almost twice as much air to hit the surface. During that time, more UV light is scattered out, lowering the UV index. 

That same property applies to higher elevations as well. The higher up you go, the less atmospheric scattering is able to remove UV light. That's why sunburns are such a huge danger on mountain peaks despite the temperatures being much cooler than at the lake or beach here in Texas.

Being on the water can end up a double whammy, too. The water reflects the sunlight, effectively enhancing the UV dose you're receiving. It can also wash away your sunscreen if you don't reapply regularly. The same can happen with sweat from the brutal Texas heat.