Wind chill and frostbite

Wind chill is the temperature the air feels like to people and animals outdoors. Wind carries heat away from bare skin, which lowers the skin's temperature and, in time, the body's. So at an air temperature of 0°F with a 15 mph wind, the wind chill is −19°F, and exposed skin can freeze in 30 minutes. Wind chill is only defined at temperatures of 50°F or below and wind speeds above 3 mph. Bright sunshine can raise it by 10°F to 18°F.

What wind chill does and doesn't do

Wind chill acts on bodies, not things. It makes a car radiator or a water pipe cool faster, but never below the actual air temperature. At −5°F with a wind chill of −31°F, the radiator gets no colder than −5°F.

Frostbite needs an air temperature below freezing. When the thermometer reads above 32°F, a wind chill below freezing can't give you frostbite. It can still lead to hypothermia after a long time outside.

Frostbite

Frostbite is body tissue freezing. To protect the organs, the body cuts circulation to the hands, feet, nose and ears, and those areas freeze first. It can happen within minutes, on any exposed skin.

Redness or pain in the skin may be the first sign. Then come numbness and skin that turns white or grayish-yellow, or feels firm or waxy. If you think someone has frostbite:

• Get them inside to a warm room.
• Take off rings, watches and other tight jewelry.
• Warm the area slowly, in warm, not hot, water. Wrap the face and ears in a moist, warm towel.
• Keep them off a frostbitten foot, since walking can cause more damage.
• Don't use a fireplace or other radiant heat, which can burn numb skin.
• Leave any blisters alone, since breaking them can cause scarring and infection.

Skin that turns blue or gray, swells badly, blisters or feels hard and numb under the surface needs a hospital as soon as possible.

Hypothermia

Hypothermia is a body temperature below 95°F, and it's an emergency. The signs are uncontrollable shivering, memory loss, confusion, slurred speech, drowsiness and exhaustion. It can happen at temperatures as warm as 60°F, especially in water or after a long time outside without enough clothing.

Call for medical help first. Then get the person inside, into dry clothing and wrapped in a warm blanket, with the head and neck covered. Warm the center of the body first, not the arms and legs. Warming the limbs first drives cold blood to the heart and can make the body temperature drop further. Give warm broth or food, not alcohol, coffee or anything hot, and don't rub the person.

Babies under 2 and adults over 65 are the most likely to get hypothermia, and about 20% of cold-related deaths happen at home. Keeping the thermostat above 69°F helps.

Dressing for it

Wear several layers of loose, lightweight, warm clothing. The air trapped between layers holds heat, and you can take one off before you start to sweat. The outer layer should be tightly woven, water-repellent and hooded. Add a hat and mittens, and cover as much skin as you can, and change out of wet clothes as soon as you're back inside.

An annotated example

What to do next

Check the wind chill in the forecast, not just the temperature, before you plan time outdoors. The coldest part of the day is usually early morning. Put hats, gloves and a dry change of clothes in the car. During extreme cold, keep the tank at least half full so you can stay warm if you're stranded. Winter storm checklist for the house, the car and you covers the rest of the house.