SIOUX FALLS, S.D. (KELO) — It is hot in KELOLAND Monday, with 29 South Dakota counties under an excessive heat warning and other areas under a heat advisory.

The hottest areas of the state can expect a heat index of up to 110 degrees, but heat index, the combination of air temperature and relative humidity, isn’t the only index that people should be concerned about.

There is also the UV Index.

KELOLAND Weather online resources

According to the U.S. Environmental Protection Agency (EPA) the UV Index tells the expected risk of overexposure to UV radiation from the sun.

The National Weather Service (NWS) says UV radiation can lead to reddening skin in humans, as well as development of skin cancer, cataracts and suppression of the immune system.

While some UV radiation is needed by humans, too much can be harmful. That’s where the UV index comes into play.

KELOLAND Meteorologist Scot Mundt says that the strength of UV radiation comes down, in large part, to the time of year and the amount of cloud cover, with more cloud cover resulting in fewer UV rays reaching the ground.

Mundt says the time of year with the highest UV Index is, unsurprisingly, the summer months.

“The winter’s UV index is very low,” he said. “On a day like today, you expect it to be high due to a lot of sunshine and a more direct sun angle.”

And high it is.

According to the EPA, the UV Index forecast for Monday, July 18 in Sioux Falls is 9.

KELOLAND News

That 9 comes on a scale of <2 to 11+.

On the scale of severity, <2 is categorized as low; 3 to 5 is moderate; 6 to7 is high; 8 to 10 is very high; and 11+ is extreme.

In that very high UV range, the EPA offers tips to protect your skin from damage. First of all, they highlight the hours of 10 a.m. to 4 p.m. as the most dangerous for UV exposure, and say a shirt, hat and sunscreen are a must. Seeking shade is also recommended when possible.

For those hitting lakes, rivers or pools, they offer a further note of caution. “Beachgoers should know that white sand and other bright surfaces reflect UV and can double UV exposure.”

Mundt’s big takeaway for a high UV day?

“It’s a good idea to reapply sunscreen if spending time outside.”