How Weather Affects the UV Index (Yes, You Can Burn on a Cloudy Day)

Author : Feddersen Day | Published On : 30 Apr 2025

Have you ever checked the UV index today and thought, “It's cloudy, so I’m probably fine”? Well, not so fast. Just because you can't see the sun doesn’t mean the sun isn’t seeing you. Surprisingly, you can still get sunburned even on a cloudy day—and sometimes even faster than when it’s sunny!

The UV index is a measure of the strength of ultraviolet (UV) rays from the sun. UV rays are the invisible part of sunlight that can harm your skin and eyes. A higher number means a greater risk of sunburn. But here’s the twist: just because it’s overcast doesn’t always mean those rays are blocked.

Clouds don’t block all UV rays. In fact, they might only filter about 20% of them, and in some cases, they can even make the situation worse. Certain cloud types, like thin white clouds, can actually reflect and scatter UV rays, making them hit the ground more strongly. So, if current UV index ’re outside thinking the clouds have your back—think again.

Weather plays a big role in the daily changes of UV levels. For example, after it rains, the cleaner air can let more UV rays through. Snow on the ground can reflect UV rays, too—so winter doesn’t mean you're safe from sunburn either. Windy or cool weather might trick you into thinking you're not getting much sun, but UV rays don’t care about temperature. You can burn even when it feels chilly.

Here’s another surprise: elevation makes a difference. If you live or vacation in the mountains, UV radiation increases as you gain height. So, that cool mountain air isn’t protecting you either.

So what should you do? Get in the habit of checking the UV index each day, even if it’s cloudy. And don’t skip sun protection just because the weather seems mild. Wearing sunscreen, sunglasses, and a hat can make a big difference. Light clouds won’t stop UV rays from reaching your skin, and you don’t want to end the day with a surprise sunburn.

Weather can be tricky, and UV rays even trickier. Always take a moment to think about sun safety, no matter what the sky looks like. Your skin will thank you later!