Not all winter storms are the same, of course. They come in different varieties and can affect different regions with many different weather conditions.
A massive winter storm is poised to impact more than a third of the U.S. population in the coming days, and ice – especially in Southern regions that aren't always equipped to withstand it – is one of the main conditions meteorologists are warning about.
The system could rival the March 1993 so-called "Storm of the Century," Marshall Shepherd, director of the Atmospheric Sciences Program at the University of Georgia and former president of the American Meteorological Society, told ABC News. That winter storm struck the Florida Gulf Coast with 90 mph winds but became a blizzard as it moved up the East Coast, ultimately affecting some 22 states and causing $2 billion in property damage.
The scale of the current storm is expected to be even larger, impacting at least 30 states from the southern Rockies to the East Coast, Shepherd said.
Regions in the northern part of the storm will experience snow, but to the south, states including Texas, Mississippi, Alabama, Georgia, the Carolinas and southern Virginia will experience a "massive" ice and sleet storm, according to Shepherd.
An ice storm occurs when freezing rain – defined as supercooled water that freezes on contact with exposed surfaces – is the dominant precipitation in a winter storm.
If there’s a layer of freezing or below freezing air that's close to the surface, the precipitation falls as snow, Samantha Borisoff, a climatologist with the Northeast Regional Climate Center at Cornell University, told ABC News. When there’s a layer of air higher above the surface that’s above freezing, that’s when sleet – defined as ice pellets – and freezing rain can occur.
The difference is how close to the surface that warm layer is, Borisoff said. For sleet, the warm layer is shallow, or closest to the surface, so freezing and refreezing occurs and ice pellets fall. For freezing rain, the warm layer is deep, or just above the shallow layer, so precipitation falls as rain and freezes when it touches the surface.
Ice storms are specifically defined as storms that result in ice accumulations of at least a quarter of an inch on exposed surfaces, according to the National Weather Service.
Ice accumulations of a quarter inch or more are usually considered significant and possibly damaging. It only takes a quarter of an inch to glaze roads and seriously impact travel, according to the Midwest Regional Climate Center (MRCC).
Freezing rain can coat roads, trees, power lines and other exposed surfaces with a layer of ice, creating slippery and potentially dangerous conditions.
Ice can significantly weigh down on trees and power lines, according to the MRCC. A half an inch of ice coating a tree limb or power line can add hundreds of pounds of weight, causing them to sag or even snap.
The current storm will also include occasional wind gusts of 20 to 30 mph, which could exacerbate the stress on trees and power lines, Shepherd said, increasing the likelihood that they may fail.
The severity of an ice storm is determined by how much rain falls and how much ice accumulates, the strength of the wind, and whether the storm strikes an urban or rural area, according to the MRCC.
Urban areas tend to suffer more economic and physical damage than rural areas because there is a higher concentration of utilities and transportation systems. A greater number of buildings and roads also means there are more surfaces on which ice can accumulate and potentially cause problems.
Most precipitation in the winter begins as snowflakes and ice crystals, because high-altitude temperatures at the top of the clouds are below freezing. If the temperature from the clouds to the ground remains at or below 32 degrees Fahrenheit, the precipitation falls as snow.
However, if there's a layer of warmer air between two layers of air with temperatures at or below freezing, the snowflakes can melt in the warmer layer and then pass through the lower, colder layer without re-freezing. The key is that the melted snow needs to remain cold enough as it falls to freeze when it hits an exposed surface, becoming freezing rain.
The winter storm is expected to move into the South on Friday afternoon. By Friday evening, Dallas, Texas, will see a wintry mix, and Oklahoma and Kansas will begin to get some snow.
On Saturday morning, the snow and ice is expected to move from Dallas to Little Rock, Arkansas, and then to Memphis, Tennessee. By Saturday afternoon, the snow and ice could stretch east into Georgia and the Carolinas.
The storm will move into the Northeast on Sunday, likely bringing plowable accumulations of snow to the Northeast.
The storm has the potential to drop "notable" snowfall amounts on some larger cities of the Interstate 95 corridor, such as Washington, D.C., Philadelphia, and New York City, Borisoff said.
By the Monday morning commute, 6 to 12 inches of accumulated snow is possible, although expected snow totals are not yet clear for the region.
"The storm is still a few days out, so the forecast will shift in the coming days," Borisoff said.
The lack of heat will be dangerous in several major cities – including Dallas, Little Rock and Memphis – especially as brutally cold temperatures move in after the precipitation passes.
"If people are losing power in this extreme cold, that's a hazard, too," Shepherd said.
People in the storm's path should have items like extra food and water, flashlights, batteries and extra medication on hand in case of power outages, which could potentially last days, Borisoff said.
The South is especially ill-equipped to handle ice and sleet, simply because the typical regional climate has not historically required an infrastructure to deal with such severe winter storms, Shepherd said.
"We don't get this kind of weather often," he said. "Should we invest infrastructure in something that happens occasionally?"
Ice storms also can make travel very dangerous, Borisoff said.
"People should stay off the roads unless it’s an emergency as travel can be extremely dangerous during ice storms," she said. "If they need to travel, make sure to have an emergency kit that includes items such as a shovel, blankets, flashlights, first-aid kit, food, and water."