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KEEP AN EYE ON THE WIND CHILL

NOAA collage of winter scenes.Jan. 15, 2004 — With an arctic airmass spreading over much of the northeastern U.S., the NOAA National Weather Service reminds residents in those affected areas to keep an eye on the wind chill, as well as the outside temperatures.

At 9:00 a.m. EST, the wind chill ranged from minus 7 in Central Park, N.Y., (actual temperature of 10 degrees F) to minus 76 at Mt. Washington, N.H., (actual temperature of minus 11). Boston, Mass., was shivering with a minus 17 wind chill, Albany, N.Y., at minus 27, and Bangor, Maine., at minus 31.

 

NOAA image of NOAA National Weather Service forecast office in Gray, Maine, taken several years ago during high winds and severe wind chills.Wind chill is the term used to describe the rate of heat loss on the human body resulting from the combined effect of low temperature and wind. As winds increase, heat is carried away from the body at a faster rate, driving down both the skin temperature and eventually the internal body temperature. The wind chill index combines the temperature and wind speed to let you know how cold the wind “feels” against your skin. While exposure to low wind chills can be life threatening to both humans and animals alike, the only impact that wind chill has on inanimate objects, such as vehicles, is that it shortens the time that it takes the object to cool to the actual air temperature (it cannot cool the object down below that temperature). (Click NOAA image for larger view of NOAA National Weather Service forecast office in Gray, Maine, taken March 17, 2000, during high winds and severe wind chills. The temperature was about 17 degrees with a wind speed of about 25 mph producing a wind chill of about minus 1 degree Fahrenheit. Please credit “NOAA.”)

During times of adverse cold weather, wind chill advisories and warnings are issued by the NOAA National Weather Service to alert the public of the impending threat. Criteria varies slightly to reflect local conditions, but in general, wind chill warnings are typically issued when the wind chill is 20 below zero or lower. During these weather conditions, exposed flesh can freeze in less than 30 minutes.

Here are some Preparedness Tips for the Remainder of the Week.

  • Avoid prolonged exposure to the cold and wind. Stay indoors if possible.
  • Wear layered clothing. Each layer of clothing traps a small amount of air that helps insulate the body from the outside cold and wind. The top layers will cut down on the
    penetration of the wind, allowing the lower layers to trap heat, thus lowering the amount of heat that the wind can carry away from the body. Wear a hat, since half of your body heat can be lost through your head.
  • If traveling, carry a fully charged cell phone. Let others know your travel plans. Pack extra clothes or sleeping bags inside your vehicle. If you become stranded, stay inside your vehicle and out of the wind.
  • Make sure your vehicle is in good working order. Keep the gasoline tank full for emergency use and to keep ice from forming inside your gas tank.

In 2001, the NOAA National Weather Service started using a new formula that includes specific wind chill threshold values showing frostbite danger at given periods of time. The new wind chill index takes into consideration the following.

  • The calculated wind speed at an average height of five feet (typical height of an adult human face) based on readings from the national standard height of 33 feet (typical height of an anemometer);
  • The human face model;
  • Modern heat transfer theory (heat loss from the body to its surroundings, during cold and breezy/windy days);
  • Calm wind;
  • A consistent standard for skin tissue resistance; and
  • Assume no impact from the sun (i.e. clear night sky).

DANGEROUS COLD WEATHER
To understand the dangers and warning signs associated with the cold, let's examine how the human body regulates its temperature.

HYPOTHERMIA
The human body loses heat during the winter due to the conduction and convection of heat from the skin to nearby air, due to evaporation of moisture from the skin surface, and due to normal respiration. To compensate for this heat loss, the body burns energy to produce heat to keep the body temperature at a relatively constant level. If, however, a body loses heat faster than it can produce heat, the body temperature will cool to below normal levels, a medical condition known as hypothermia.

Hypothermia will gradually worsen unless the overall rate of heat loss can be stopped. The warning signs for hypothermia may start with shivering and shaking and may end in death. Initially, as the body temperature starts to drop, shivering begins. At the same time, the brain begins to reduce the amount of blood that is circulated to the extremities of the body in order to conserve heat for the vital organs near the body's central core. If the central core of the body continues to cool, uncontrollable shaking, memory loss, disorientation, incoherence, slurred speech, drowsiness and apparent exhaustion may develop. These are all signs of a very serious situation. If the body core temperature drops below 95 degrees Fahrenheit, just 4 degrees below normal, immediate care is needed, as the person will likely become irrational. Once the body core temperature drops below 90 degrees, the person loses muscle control,
and outside help is the person's only hope for survival. If that help is not available, heart and/or respiratory failure and death will eventually follow as the core temperature continues to drop.

If a person is suffering from hypothermia, it's critically important that the person be warmed properly. If warmed improperly, death may result. In a hypothermic person, cold blood is concentrated in the extremities. If these extremities are warmed too quickly, this cold blood will be released into the body's central core, possibly lowering the central core temperature to a fatal level. Use the following steps to raise the core temperature of a hypothermic person.

  • Get the person into dry clothing if their clothes are wet.
  • Put on additional clothing to warm the person's head and trunk, such as a hat and vest.
  • Wrap the person in a warm blanket and be sure their head and neck are covered. Do not cover their extremities.
  • Give them warm liquids to drink, but no alcohol, drugs or coffee.
  • Seek medical attention, if necessary.
  • Hypothermia can also develop in elderly people in a cool room with few, if any, warning signs.

FROSTBITE
Frostbite is a condition in which the body tissue actually freezes. Frostbite is often associated with hypothermia. In a hypothermic person, the brain greatly reduces the amount of blood that is circulated to the extremities of the body and they begin to cool. This increases the chances that the tissue at the end of the extremity may actually freeze. The most susceptible areas for frostbite include the fingers, toes, nose and ear lobes.

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Relevant Web Sites
NOAA National Weather Service

NOAA National Weather Service Wind Chill Index

NOAA Winter Weather Awareness

Media Contact:
Susan Weaver, NOAA National Weather Service, (301) 713-0622
(Photo courtesy of John Jensenius of the NOAA National Weather Service forecast office in Gray, Maine.)