5 Things to Know About Ice Storms

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We are currently monitoring the potential for significant ice accumulations in the Appalachians from Winter Storm Avery. For the latest forecast on Avery, click here.

Here are five things you need to know about ice storms and how to prepare.

1. What Causes an Ice Storm

Ice forms when freezing rain accumulates on surfaces and the ground.

Freezing rain occurs when air warmer than the freezing mark above the ground moves over subfreezing air near the ground. When snow aloft falls through the warmer layer, it melts into rain. Then, as the rain droplets fall into the shallow layer of subfreezing air, the droplets freeze upon contact. This creates a glaze of ice.

(MORE: The Difference Between Sleet and Freezing Rain)

In most areas of the U.S., an ice storm typically refers to events in which a quarter-inch of ice accumulation occurs, producing a significant and possibly damaging accretion of ice.

If less than a quarter-inch of ice is produced, it's usually more of a nuisance event with less severe impacts. However, it's important to remember that even a light glaze of ice can make travel hazardous.

2. Significant Impacts are Possible

When a quarter-inch or more of ice builds up, severe impacts can result.

Ice can increase the weight of tree branches by up to 30 times and can add 500 pounds of extra weight to power lines. Consequently, tree branches, power lines and power poles can fall.

This damage to trees and power lines can begin when ice accumulates between a quarter- and half-inch. Roads also become slippery at this stage.

When more than half-inch of accumulation occurs, widespread damage to trees and power lines can be expected, and roads become impassable.

(MORE: What Ice Storm Accumulations Mean)

If strong, gusty winds accompany freezing rain, the chance for damage increases due to the added stress on trees and power lines.

Downed trees can block roads, making driving even more dangerous.

3. Ice Storms and Their Impacts Can Last for Days

Depending on the severity of the ice storm and the weather pattern, impacts can persist for days.

This can result in a loss of electricity and heat for several days. In some cases, hypothermia can become a concern due to the prolonged cold conditions and lack of heat.

The other factor to consider is how cold it will be after the storm. If temperatures do not rise above the freezing mark, then not much melting will take place, especially in areas where there isn't much sun.

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This is especially important in areas such as the South, where there is limited equipment and supplies to treat roadways.

One other consideration is if melting does occur and then the temperature drops below freezing, black ice can form, resulting in additional slippery travel conditions.

4. You Need to Prepare Ahead of Time

To mitigate the potential impacts that can occur from an ice storm, it's necessary to prepare ahead of time.

If you're stuck at home for several days, make sure you have enough non-perishable food and any supplies you may need, including water, a cooler with ice and prescriptions. If you have canned foods, be sure to have a non-electric can opener.

If you lose power. it is a good idea to have flashlights, batteries and candles on hand. Remember to keep the doors to the refrigerator and freezer closed to help keep the food cold.

Charge any necessary electronics such as your cell phone. If possible, have a secondary source of heat.

You should also have a first-aid kit, some cash and have your vehicle filled with gas, according to FEMA.

Consider pruning limbs or removing trees leaning toward your home before the ice storm to avoid the potential of falling trees or limbs onto your home.

5. They've Happened Many Times Before 

One of the most devastating ice storms happened in portions of northern New England, upstate New York and southeastern Canada Jan. 5-9, 1998. Ice accumulated up to 3 inches in some areas, resulting in extensive power outages that lasted for days and, in some cases, weeks. Damages totaled $1.4 billion in the U.S. and $3 billion in Canada. Sixteen deaths were reported in the U.S. and 28 in Canada.

(MORE: The Nation's Worse Ice Storms)

Many ice storms take place in the South, including one in February 1994, which impacted areas from Texas and Oklahoma eastward to the Carolinas. More than 2 million lost power. Some residents in Mississippi were without power a month after the storm. At least nine deaths were attributed to the storm.

More recently, Winter Storm Goliath brought ice from areas in the southern Plains into the Midwest in late-December 2015. Up to 1 inch of ice was reported near Yukon, Oklahoma, and a quarter-inch of ice downed numerous power lines and trees in Monmouth, Illinois.

A month before Goliath, Winter Storm Cara brought icy conditions to the southern Plains. Winds, freezing rain and sleet affected power lines northwest of Oklahoma City, leaving more than 100,000 customers without power, many for up to a week.