(NewsNation) — The holiday season may have come and gone, but as the popular Christmas song goes, the weather outside is frightful.

Much of the United States is facing brutally cold temperatures, with about 150 million Americans under a wind chill warning or advisory for dangerous and cold wind, Zack Taylor, a meteorologist with the National Weather Service in College Park, Maryland, told the Associated Press Monday.

Some places like northern and northeast Montana saw temperatures as low as minus 40 degrees Fahrenheit, while Kansas, Missouri, Illinois and parts of Indiana were facing subzero lows.

To make sure you and your loved ones are safe, the Centers for Disease Control and Prevention say being prepared is the best defense.

If you’re going out

The National Weather Service suggests minimizing travel and staying indoors during the worst part of the extreme cold. If you must travel, however, wear layers of loose-fitting, lightweight, warm clothes and a hat. Mittens, the NWS said, are better than gloves, and you should cover your mouth to protect your lungs from the cold.

If you’re driving, keep a winter survival kit in your vehicle equipped with water, food, a flashlight, extra batteries, and other supplies, the NWS says.

It’s important to stay dry and out of the wind.

Warning Signs of Hypothermia

Hypothermia is when the body loses heat faster than it is produced when exposed to very cold temperatures for a long time, the Centers for Disease Control and Prevention said. This can affect the brain, making it hard for the victim to think clearly or move well. In some cases, a person may not know that they have hypothermia.

Especially susceptible are older adults with inadequate food, clothing or heating; babies in cold bedrooms; those who remain outdoors for a long time, such as people without homes or hunters, and people who drink alcohol or use other drugs.

Symptoms in adults include shivering, exhaustion or feeling very tired, confusion, fumbling hands, memory loss, slurred speech and drowsiness. Babies might have bright red, cold skin and very low energy.

If you think someone has hypothermia, it is imperative to get them into a warm room or shelter and remove any warm clothing they’re wearing. You should warm their chest, neck, head, and groin using an electric blanket or with skin-to-skin contact under loose, dry layers of blankets, clothing, towels or sheets. Warm drinks can also help.

Once their body temperature has increased, keep the person affected dry and wrap their body in a warm blanket. Get them medical attention as soon as possible.

Someone with severe hypothermia may be unconscious or seem to not have a pulse. Even if they appear dead, the CDC says, you should still perform CPR.

“In some cases, hypothermia victims who appear to be dead can be successfully resuscitated,” the CDC said.

Prevent Frostbite

Frostbite, the CDC said, is a “type of injury caused by freezing” that leads to a loss of feeling and color, usually in the extremities. In some cases, it can permanently damage the body and even lead to amputation.

Those with poor blood circulation are especially at risk as well as those not properly dressed for cold temperatures.

The CDC says that redness or pain in any “skin area” is a sign you should get out of the cold or protect exposed skin. A white or grayish-yellow skin area, skin that feels unusually firm or waxy and numbness are general signs of frostbite.

You should seek medical care if you or someone else has frostbite, but if it isn’t available and there are no signs of hypothermia, the CDC says to:

• Get the affected person into a warm room
• Keep them off their feet or toes that show signs of frostbite
• Do not rub or massage the frostbitten area
• Put the areas affected in warm, not hot, water or use body heat if water’s not available
• Do not use a heating pad, heat lamp or warmth from a stove, fireplace or radiator, as frostbitten areas can burn easily

Staying Indoors?

Those hunkering down inside should also take some precautions, per the CDC.

You should have an alternative heat source in case the power goes out, such as extra blankets, sleeping bags and coats; an up-to-code fireplace; portable space heaters or kerosene heaters. (The CDC says to check with your fire department to ensure kerosene heaters are legal in your area, though.)

Electric space heaters should have automatic shut-off switches and be kept away from flammable materials, the CDC said, and fireplaces, wood stoves or other combustion heaters should only be used if they are properly vented. They should also never be placed on furniture or near water. In addition, don’t let children alone near space heaters.

A qualified technician should service your heating system every year, and you should only use the type of fuel your heater is designed to use.

Should the power go out, it’s better to use battery-powered flashlights or lanterns, the CDC says, but if you must use candles, never leave them unattended.

The Associated Press contributed to this report.