What is the UV Index (and Why Should I Care About It)?

iStock
iStock

We’re so used to running for cover when we hear a rumble of thunder during the summer that it’s easy to forget that we’re just as exposed to the elements under a beautiful, cloud-free sky. Whenever the Sun's out (and even when it isn't), we're at risk for sunburns, which are caused by the Sun's ultraviolet, or UV, radiation. But just how serious is that risk on a given day? That's where the UV Index comes in.

Ultraviolet radiation falls next to visible light on the electromagnetic spectrum. The two wavelengths of UV rays that can cause injury are called UVA and UVB rays. Both types are dangerous over long periods of time, but UVB rays are thought to be the most dangerous. Excessive exposure to UVA and UVB rays can cause cell death, leading to painful sunburn, or, over time, some forms of skin cancer.

Earth’s atmosphere does a pretty good job protecting us from harmful UV rays, but it doesn’t completely block them out. Most ultraviolet radiation is absorbed by the ozone layer. Ozone is gas that’s usually situated more than twice as high above sea level as the cruising altitude of a commercial airliner. In the 1970s and 1980s, there was a concerted effort to eliminate the use of chemicals that deplete the ozone layer as people began to understand what its depletion would mean: overexposure to dangerous UV rays for humans, animals, and plants.

UV Index Forecast
A map of the UV Index on June 9, 2017.
NOAA/NWS/EPA

The UV Index was developed to tell us the level of solar radiation on a particular day, and thus, how susceptible we are to a sunburn. The UV Index is an open-ended scale that starts at 0, indicating the lowest level of danger, with the risk gradually increasing through a UV Index of 10. Any value above 10 indicates an extreme risk for harm from UV rays, with sunburns and eye damage occurring in just minutes.

The index is compiled daily using factors like ozone concentration in the atmosphere, expected cloud cover, and the elevation of a certain point above sea level. Greater ozone concentrations, more clouds, and a lower elevation will help prevent UV rays from reaching the ground. A bright, hot, sunny day can easily cause the UV Index to soar above 10.

Risk from UV rays doesn’t end with sunshine pouring out of the sky. Ultraviolet radiation can also be reflected, meaning that the danger for sunburns and eye damage increases around bright surfaces like a beach or the shimmering waters of a swimming pool. If your eyes have ever hurt after looking at snow on a sunny day, that painful condition is directly caused by UV rays reflecting off of the white surface.

One easy way to protect yourself from harmful UV radiation is to cover up. But clothing and hats don't deflect all UV rays. That's where sunscreen comes in. The best sunscreen to use is one that’s rated for both UVA and UVB protection with an SPF (sun protection factor) of at least 15 or higher, according to the FDA. (The American Academy of Dermatology suggests one with an SPF of 30 or higher.) A sunscreen’s SPF doesn’t relate to the amount of time you can spend in the sun, but rather the amount of protection offered by a particular formula. An SPF of 15 blocks 93 percent of UV rays, while SPF 50 is said to block 98 percent. (Some argue that sunscreens over SPF 30 are no more effective.) Whichever SPF you choose, don't forget the sunglasses—specially rated pairs can protect your eyes from radiation, and also help you channel your inner celebrity. Sounds like a win-win to us.

Fall Foliage Is Running Late This Year

Free art director/iStock via Getty Images
Free art director/iStock via Getty Images

The August arrival of the pumpkin spice latte might have you feeling like fall is in full swing already, but plants aren’t quite so impressionable. According to Travel + Leisure, the best fall foliage could be coming a little later than usual this year.

Historically, the vibrant transformation starts to sweep through northern regions of the Rocky Mountains, Minnesota, and New England in mid-September, and reaches its peak by the end of the month. Other areas, including the Appalachians and Midwest states, don’t see the brightest autumn leaves until early or mid-October. The Weather Channel reports that this year, however, the forecast from the National Oceanic and Atmospheric Administration predicts unseasonably warm temperatures for the next two weeks, which could impede the color-changing process.

Warm temperatures aren’t necessarily bad for fall foliage, as long as they occur during the day and are offset by cool nights. Since meteorologists don’t expect the overnight temperatures to drop off yet, plants will likely continue producing enough chlorophyll to keep their leaves green in the coming days.

The good news is that this year’s fall foliage should only be about a week late, and meteorologist David Epstein thinks that when leaves do start to change color, we’re in for an especially beautiful treat. If the current weather forecast holds, he told Boston.com, we'll "see a longer season than last year, we’d see a more vibrant season than last year, and it would come on a little earlier than last year, which was so late.”

Though poor weather conditions like early snow, heavy rain, drought, or strong winds can cause leaves to fall prematurely, most trees right now are in a good position to deliver a brilliant display of color after a healthy, rain-filled summer.

Find out when you’ll experience peak fall foliage in your area with this interactive map.

[h/t Travel + Leisure]

Amazing Timelapse Shows Florida Sky Turning Purple Following Hurricane Dorian

Scott Olson/Getty Images
Scott Olson/Getty Images

Photographs taken of Hurricane Dorian's massive eye and the damage it caused in the Bahamas paint a picture of what it was like to live through the historic storm. But some of the most stunning images to come out of the event were captured after the hurricane had passed. As KENS5 reports, the time-lapse video below shows the sky over Florida turning a unique shade of purple in the wake of Hurricane Dorian.

Dorian skimmed the east side of Florida earlier this week, causing power outages and some flooding. The worst of the storm was over by Wednesday night, but the ominous purple clouds it left behind may have sparked concern among some Florida residents.

A purple sky following a hurricane is the result of a perfectly natural occurrence called scattering. The sky was super-saturated after Dorian arrived, and the moisture in the atmosphere refracted the light of the setting sun. Normally, only the longest wavelengths of light on the color spectrum are visible through the clouds—that's why sunsets often appear gold, pink, and orange.

Violet is the shortest wavelength on the spectrum, which means it's almost never visible in the sky. But the air's high dew point Wednesday night, combined with the dense low-hanging clouds, created the perfect conditions for a rare purple sky.

Locals who've lived through a few hurricanes may have recognized the phenomenon; the same thing happened after Hurricane Michael hit Florida last year.

[h/t KENS5]

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