National Weather Service meteorologist John Pollack says exposed flesh will freeze in about 15 to 30 minutes when the wind chill is 20 below.

A wind-chill advisory is in effect until late this morning. Temperatures of five to 10 below combined with winds of at least 10 miles per hour are creating dangerous conditions.

Temperatures should raise by 11 a.m. Tuesday.

A mass of arctic air moving over the Great Plains created the severe cold, which hit most of Nebraska yesterday. The cold follows a weekend storm that dumped up to six inches of snow over the area.

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Preparing for Cold Weather

• Be alert to weather changes

  Pay close attention to weather changes, especially when the temperature falls quickly within a short period of time.

• Put on adequate clothing

  Put on dry, light and comfortable clothes that are good for keeping warm. Do not put on clothes that are too bulky, and do not dress too tightly, which may restrict blood circulation or hinder body movements. Be sure to keep the head, neck, hands and feet warm.

• Sufficient food and drink

  Eat and drink hot and easily digestible food and beverages with higher calories, like hot milk, soup, noodles and rice. Alcohol is not a good means for keeping warm. Although one feels warm immediately after drinking alcohol, it actually accelerates the loss of body heat, as alcohol dilates blood vessels.

• Keep your home warm

  Keep your home warm, but well ventilated. To keep out drafts, repair cracks in windows, doors and walls. When using electric heaters, make sure there is indoor ventilation. Do not overload the electrical sockets which could overheat and lead to fire or burn injuries.

Hypothermia

What is hypothermia?

• Hypothermia occurs when your body's control mechanisms fail to maintain a normal body temperature.

• Normal core body temperature can range between 98.9 F and 99.9 F. An internal body temperature of 95 F or lower signals hypothermia.

• Signs and symptoms that may develop include gradual loss of mental and physical ability. Severe hypothermia can lead to death.

• Nearly 700 Americans die of hypothermia each year.

• Those at greatest risk are older adults, who account for half of hypothermia-related deaths, and children.

Tips to avoiding hypothermia

Before you or your children step out into cold air temperatures, remember this simple advice: C-O-L-D.

• C for Cover Wear a hat or other protective covering to prevent body heat from escaping from your head, face and neck. Cover your hands with mittens instead of gloves. Mittens are more effective than gloves are because mittens keep your fingers in closer contact with one another.

• O for Overexertion Avoid activities that would cause you to sweat a lot. The combination of wet clothing and cold weather can give you the chills.

• L for Layers Wear loose-fitting, layered, lightweight clothing. Outer clothing made of tightly woven, water repellent material is best.

• D for Dry Stay as dry as possible. In the winter, pay special attention to places where snow can enter, such as in loose mittens or snow boots.

Source: A compilation of Web Reports contributed to this report.