Wind Chill Can Ruin Sunny Winter Hikes—Unless You’re Prepared.

Wind can mislead beginner hikers. It could be a sunny day without a cloud in the sky with average temperatures until whoosh, you’re caught in Arctic temperatures.

Why does this happen? Through a process called convection, wind carries heat away from your skin, making the air temperature feel colder than it actually is. If you’re out in the elements long enough, your body temperature starts to drop, too. There is a way to measure for the adjusted temperature called wind chill: Depending on wind speeds, temperatures can drop by as much as 50 degrees Fahrenheit, so it is crucial to plan ahead and dress accordingly.

The National Weather Service’s formula to calculate wind chill is: 35.74 + 0.6215T – 35.75(V^0.16) + 0.4275T(V^0.16). Simple, right?

Let’s break it down: Here, T represents air temperature in Fahrenheit and V represents wind speed in miles per hour. (Humidity does not affect the overall wind chill enough to be considered a factor.) The equation only works for temperatures at or below 50°F and gusts above 3 mph.

Not in the mood to break out the calculator? Check out the chart below.

With wind chill, timing is everything. If the gusts are strong enough and you’re out in the elements long enough, you can get frostbite in above-freezing temperatures. (In addition to following advice for avoiding hypothermia and frostbite, sit with your back to the wind, if possible, when taking breaks on the trail.)

Dress for wind chill

In gusty conditions, one of the best things you can do is dress to stay warm and dry. This means wearing several layers: a sweat-wicking base layer, an insulating mid layer, and a windproof outer shell. Add and remove layers as you hike to prevent excessive sweating (and hypothermia). Any skin exposed to the elements could be prone to frostbite. Also, the weather app pre-programmed on your phone may not account for wind chill; don’t dress for that base temperature. Check National Weather Service, Mountain Forecast, or Weather Underground to evaluate wind speeds and prepare for wind chill.

Don’t forget to pack these for chilly, windy hikes:

• To protect your hands, wear mittens or gloves, and to protect your feet, wear thick wool socks (but not too thick that your boots are too tight and your feet don’t get enough circulation).
• Wear a neck gaiter over your mouth and nose to keep your face warm.
• Shield your eyes with goggles or glasses. Wind can carry debris into your eyes and also dry them out. Be sure to wear the correct glass tint for the elements you’re in, too.
• Because heat comes out from your head and wind will carry heat away, wear an insulating hat or beanie.
• If you’re wearing waterproof gaiters on your boots, make sure snow stays out. Wet feet are cold feet.

When is it too windy to hike?

There’s a difference between embarking on a blustery hike and holding on to literally anything to prevent being blown off the cliff. For beginner hikers, wind blowing at 32 mph or above—enough to make trees sway—will be difficult and dangerous to move through. Even experienced hikers should turn around in winds blowing 50 mph, which can send debris flying and will make it hard to walk. The trail will still be there in better conditions, so if you or anyone in your group feels unsafe, head back to the trailhead and try again another day. Better yet, look up trail conditions ahead of time and plan to lace up in better weather.