What Is Wind Chill?
Wind chill is how cold it feels on exposed skin when wind is added to cold air. Wind strips away the thin layer of warm air next to your skin, so you lose heat faster. The NWS wind chill is the calm-air temperature that would cause the same heat loss. It cannot cool objects below the actual air temperature.
Cold weather does not roar like a tornado. It just quietly hurts people. This is a safety lesson, so I'll keep the jokes for the sign-off. How cold feels, what makes a blizzard, and the steps that keep you and your family alive when the power goes out.
Key Takeaways
- Wind chill measures heat loss from exposed skin, not the temperature of objects.
- At a wind chill of about -20 F, frostbite can occur in about 30 minutes.
- A blizzard is defined by wind of 35 mph or more and visibility under 1/4 mile for 3 hours, not by snowfall.
- Hypothermia starts below 95 F body temperature, and shivering can stop as it worsens.
- Never run a generator, grill or camp stove indoors or in a garage.
Cold weather kills quietly. There is no roar like a tornado, but extreme cold, blowing snow and indoor heating mistakes injure and kill people every winter. This lesson covers how cold is measured and felt, what makes a blizzard, and how to stay safe.
What Does Wind Chill Mean?
Your body warms a thin layer of air right next to your skin. Wind strips that layer away and replaces it with colder air, so exposed skin loses heat faster. Wind Chill is a number that expresses this: the air temperature that would produce the same rate of heat loss from exposed skin in calm conditions.
The NWS Wind Chill Formula
The National Weather Service and Environment Canada adopted a new formula in 2001. It is based on a model of heat transfer from a human face, tested on volunteers in a chilled wind tunnel. The formula:
- Uses the air temperature and the wind speed at about 5 feet, the height of a face (not the 33 feet of a standard anemometer; the formula adjusts for this).
- Assumes a person walking into the wind at about 3 mph, with no sunshine.
- Is only defined for temperatures at or below 50 F and winds above 3 mph.
The key idea is that wind chill rises quickly at first as wind increases, then levels off. Going from calm to 15 mph matters much more than going from 30 to 45 mph.
Frostbite Times
At a wind chill of about -20 F, frostbite can occur on exposed skin in about 30 minutes. At -35 F it can happen in 10 minutes, and around -50 F in 5 minutes or less.
What Makes a Snowstorm a Blizzard?
A Blizzard is defined by wind and visibility, not snowfall amount. In the United States the NWS criteria are:
- Sustained winds or frequent gusts of 35 mph or more, and
- Considerable falling and/or blowing snow reducing visibility to less than 1/4 mile,
- For at least 3 hours.
A ground blizzard can occur with no snow falling at all, when strong winds pick up snow already on the ground. These are common on the Great Plains.
Why Blizzards Are Dangerous
- Whiteouts erase the horizon and road edges. Drivers become stranded.
- Drifts block roads and doorways.
- Wind chills in blizzards are often extreme.
- People who leave stranded vehicles to walk for help can become lost only yards from shelter.
What Are the Signs of Frostbite?
Frostbite is the freezing of skin and underlying tissue. It usually affects fingers, toes, nose, ears and cheeks.
- Early signs (frostnip): redness, then pale or white skin, tingling or numbness.
- Deeper frostbite: skin becomes hard, waxy and gray or white, and may blister after rewarming.
Get to warmth, remove wet clothing, and rewarm the area with warm (not hot) water. Do not rub frostbitten skin or use a heating pad or fire, since numb skin burns easily. Do not rewarm if there is a chance it will refreeze. Seek medical care.
What Are the Signs of Hypothermia?
Hypothermia occurs when body temperature falls below 95 F (35 C). It can happen at temperatures well above freezing if a person is wet and exposed to wind.
- Warning signs: shivering, exhaustion, confusion, fumbling hands, slurred speech, memory loss, drowsiness.
- Infants may show bright red, cold skin and very low energy.
- As it worsens, shivering can stop, which is a very bad sign.
Move the person somewhere warm, remove wet clothing, warm the center of the body first with blankets and skin-to-skin contact, give warm non-alcoholic drinks if they are alert, and get medical help right away.
How Do You Prevent Carbon Monoxide Poisoning in a Power Outage?
During winter storms and power outages, people turn to generators, space heaters and grills. Carbon Monoxide (CO) is a colorless, odorless gas produced by burning fuel. It causes headache, dizziness, nausea and confusion, and can kill sleeping people without waking them.
Dressing For Cold
- Wear layers: a moisture-wicking base, an insulating middle, and a wind- and water-resistant outer shell.
- Cover the head, face, ears and hands; mittens are warmer than gloves.
- Stay dry. Wet clothing loses much of its insulating value.
- Avoid alcohol, which increases heat loss.
Try It Here
Real-World Example: Reading A Wind Chill Warning
When dangerous wind chills are expected, your local NWS office issues a Cold Weather Advisory or an Extreme Cold Warning. The product lists expected wind chill values and how fast frostbite can happen on exposed skin. That number is the practical part. At -35 F it can take only 10 minutes.
You can compare temperature and wind at surface stations in LightningWX's Observations panel to see where the worst combinations are, but for decisions, read the official NWS product for your area and follow it.
Common Mistakes
- Myth: Wind chill can freeze my car's radiator or pipes faster than the air temperature. Fact: Wind chill only describes how fast warm things lose heat. Nothing cools below the actual air temperature, so a 20 F wind chill on a 35 F day will not freeze water.
- Myth: A blizzard means a lot of snow. Fact: A blizzard is defined by wind and visibility. A ground blizzard can happen with no snow falling at all, just strong wind lifting snow already on the ground.
- Myth: Rub frostbitten skin with snow to warm it up. Fact: Never rub it. Rewarm with warm, not hot, water, avoid fire and heating pads because numb skin burns easily, and seek medical care.
- Myth: A drink of alcohol warms you up in the cold. Fact: Alcohol increases heat loss. Give a cold person warm, non-alcoholic drinks if they are alert.
Go Deeper: How The 2001 Wind Chill Formula Works
The current NWS and Environment Canada wind chill index, adopted in 2001, replaced an older formula based on how fast water froze in a container. The new one models heat transfer from a human face. It was checked against volunteers in a chilled wind tunnel, assumes a person walking into the wind at about 3 mph, and assumes no sunshine. Wind is adjusted from the standard 33-foot anemometer height down to about 5 feet, face height.
Heat loss from skin depends on the thickness of the boundary layer of still air next to it. Wind thins that layer, and convective heat loss rises roughly with the square root of wind speed. That is why the index changes fast between calm and 15 mph and much more slowly after that. The index is only defined at or below 50 F with winds above 3 mph.
Check Yourself
No grades, no sign-in. Pick an answer and see how you did. The app keeps score for you and tracks your progress.
1 What are the US blizzard criteria?
Show The Answer
Winds of 35 mph or more and visibility under 1/4 mile for at least 3 hours A blizzard is defined by wind and visibility over time, not snow amount.
2 What does wind chill represent?
Show The Answer
The equivalent calm-air temperature for heat loss from exposed skin Wind chill measures the cooling effect on warm exposed skin; it cannot cool objects below the air temperature.
3 Which is the correct first aid for frostbite?
Show The Answer
Rewarm with warm (not hot) water and avoid rubbing Rubbing damages tissue, and numb skin burns easily near heat sources.
4 Why is running a generator in a garage dangerous?
Show The Answer
It can build up deadly carbon monoxide CO is colorless and odorless and can kill quickly in enclosed or attached spaces.
Questions People Ask
What wind chill is dangerous?
Frostbite can occur in about 30 minutes at a wind chill of -20 F, about 10 minutes at -35 F, and 5 minutes or less around -50 F.
What should I do if I'm stranded in my car in a blizzard?
Stay with your car. Run the engine about 10 minutes each hour for heat, keep the exhaust pipe clear of snow, crack a downwind window, and tie something bright to the antenna.
Can you get hypothermia above freezing?
Yes. Hypothermia can happen well above freezing if a person is wet and exposed to wind.
How far should a generator be from the house?
At least 20 feet, with the exhaust pointed away from the home. Install battery-powered carbon monoxide alarms on every level.
Are mittens or gloves warmer?
Mittens are warmer than gloves. Dress in layers, cover your head, face and ears, and stay dry.
Learn More From The Experts
- Wind Chill Chart NOAA / NWS
- Cold Weather Safety NOAA / NWS
- Winter Storm Safety: During NOAA / NWS
- Winter Weather Ready.gov
Layers on, generator outside, and if the NWS says stay home, stay home. Jen — Jen
