What Is Wind Chill And What Makes It So Dangerous?

"Wind chill" is not just a casual phrase used by meteorologists to tell you how cold it feels outside – it's a key factor in cold-weather safety.

The simple interpretation of the wind chill is how cold the air feels when the wind is factored in. This is the winter counterpart to the "heat index" when it comes to "feels-like" temperatures.

But wind chill isn't based on human comfort; rather, it's the rate that exposed skin loses heat because of the wind and cold.

W​hen the air is cold, your body naturally warms a thin layer of air just above your skin. This helps keep you from rapidly losing body heat.

Wind carries that layer of self-made insulation away from your body. Stronger wind carries that warmth away even faster, replacing that warm layer with cold air. Your body loses heat trying to warm the new cold air, the wind blows it away, and the cycle continues.

(MAP: Current Wind Chills)

T​he wind chill also isn't a meteorologist's best guess at what the air outside feels like, because it's based on the actual measured temperature and wind speed. There's an equation to calculate the wind chill (don't worry, there won't be a test).

L​uckily, people have already done the math for you, so you can use this chart to determine your wind chill.

T​his chart lets you estimate the wind chill without having to do the math yourself.

F​ind the value closest to the temperature at the top of the chart and the wind speed to the left. Your wind chill temperature is the value where the imaginary lines drawn from the air temperature and the wind intersect.

F​or example, if the temperature outside is about minus 10 degrees and the winds are about 15 mph, the wind chill is going to be about minus 32.

Y​ou can also approximate the wind chill with a little mental math: If the temperature is minus 13 degrees and the wind speed is 15 mph, the wind chill will be somewhere between minus 32 and minus 39. So you can call that a minus 35 wind chill.

W​hy Does Wind Chill Matter?

W​ind chill is important for more than just determining how cold – or, if you hate the cold, miserable – it is outside. Wind chill helps us determine the level of threat from hypothermia and frostbite.

Hypothermia

T​his happens faster when there is a colder wind chill because your body is losing heat faster as it tries to warm the layer of air around your skin.

H​owever, hypothermia deaths can happen at temperatures as warm as 30 to 50 degrees, according to the National Weather Service (NWS), especially if you are not dressed appropriately for the weather or if your skin is wet.

The NWS offers these tips to prevent hypothermia:

• Dress in layers
• Wrap up well when going outside in the cold
• Avoid breezes and drafts indoors
• Eat nutritious food and wear warm clothes to ward off winter chill
• Wear a warm hat in the winter
• Eat hot foods and drink warm drinks several times during the day
• If you live alone, ask a family member or neighbor to check on you daily

If your body temperature is 95 degrees or below, you feel cold and sluggish, or are having trouble thinking clearly, the NWS says to see your doctor immediately or go to the nearest emergency room.

Frostbite

Frostbite occurs when body tissue freezes, and it most often impacts parts of the body that are far from your heart or have poor blood circulation, like your fingers, toes, ear lobes or the tip of your nose.

In extreme cold, your body cuts circulation to your extremities in order to send more blood to your vital organs.

Y​our extremities, like your hands, feet and nose, get colder without warm blood pumping through, and eventually, fluids in your tissue start to form ice crystals.

To avoid frostbite, the best thing to do is stay inside when it's bitterly cold.

If you have to be outside, you should cover every part of your body, including your ears, nose, toes and fingers. You also want to keep your skin dry and stay out of the wind when possible.

M​ake sure none of your clothing restricts blood flow, and try to keep moving to help with blood circulation.

Be sure to stay hydrated by drinking plenty of fluids. Hydration increases your blood's volume, which helps prevent frostbite by improving circulation.

In that same vein, avoid caffeine and alcohol. Caffeine constricts your blood vessels, which will prevent the warming of your extremities. Alcohol dehydrates you and reduces shivering, which your body does to keep you warm.

According to the NWS, there are four degrees of frostbite:

• First degree: The skin's surface is frozen, known as frostnip.
• Second degree: The skin may freeze and harden; blisters form in a day or two.
• Third degree: Muscles, tendons, nerves and blood vessels freeze.
• Fourth degree: Pain lasts for more than a few hours and skin may turn dark blue or black; gangrene is a real threat and will require amputation of extremities if it occurs.