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

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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.

Denver is About to Experience Summer and Winter Temperatures Within 24 Hours

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iStock.com/mphotoi

In a story tailor-made for exhaustive Weather Channel coverage, Denver, Colorado is about to experience one of the more bizarre weather shifts in recent memory. After an expected Tuesday high of 80°F, residents can anticipate a dramatic shift down to 32°F by midday Wednesday, with an initial half-inch of snow accumulation increasing to up to 7 inches by Wednesday night.

Put another way: Citizens who need to make sure they hydrate in the warm temperatures Tuesday will have to bring out the parkas the following day.

The Denver Post reports that the warm air coming ahead of the cold can result in a clash of air masses, prompting areas of low pressure that can create forceful and damaging weather conditions. The storm could bring winds of up to 60 miles per hour and possibly even cause power outages. Snow accumulation should dissipate by the weekend, when temperatures are expected to climb back into the 60s.

The high temperature record for April 9 in Denver is 81°F, set in 1977.

[h/t The Denver Post]

What Is a Bomb Cyclone?

Maddie Meyer/Getty Images
Maddie Meyer/Getty Images

The phrase bomb cyclone has re-entered the news this week as parts of the central U.S. face severe weather. Mountain and Midwestern states, including Colorado, Nebraska, Wyoming, and South Dakota, all fall in the path of a winter storm expected to deliver tornadoes, hail, heavy snow, flooding, and hurricane-force winds on Wednesday, March 13 into Thursday. It seems appropriate for a storm that strong to have bomb in its name, but the word actually refers to a meteorological phenomenon and not the cyclone's explosive intensity.

According to The Denver Post, the bomb in bomb cyclone stands for bombogenesis. Bombogenesis occurs when a non-tropical storm experiences at least a 24 millibar (the unit used to measure barometric pressure) drop within 24 hours. Low pressure makes for intense storms, so a bomb cyclone is a system that's built up a significant amount strength in a short length of time.

This type of storm usually depends on the ocean or another large body of water for its power. During the winter, the relatively warm air coming off the ocean and the cold air above land can collide to create a sharp drop in atmospheric pressure. Also known as a winter hurricane, this effect has produced some of the worst snowstorms to ever hit the U.S.

The fact that this latest bomb cyclone has formed nowhere near the coast makes it even more remarkable. Rather, a warm, subtropical air mass and a cold, Arctic air mass crossed paths, creating the perfect conditions for a rare bombogenesis over the Rockies and Great Plains states.

Central U.S. residents in the bomb cyclone's path have taken great precautions ahead of the storm. Over 1000 flights have been canceled for Wednesday and schools throughout Colorado have closed.

[h/t The Denver Post]

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