From ice 'accretion' to supercooled water: 7 things to know about freezing rain

Snow gets a lot of the attention during winter storms, but an ice storm of freezing rain can actually have greater impacts on a region.

Snow gets a lot of attention during winter storms, but an ice storm of freezing rain can have more significant impacts on a region.

Here are 7 things to know about freezing rain:

1) It's rain that has been "supercooled"

Freezing rain begins its journey as a snowflake that then melts into a raindrop as it encounters a slice of above-freezing air on its free-fall through the atmosphere. If the air stays above freezing, it'll remain as rain.

If the raindrop encounters a renewed layer of below-freezing air, the drop will begin the process of refreezing. First, it'll become "supercooled", as in reaching temperatures at or just below freezing. And then if there is enough time to finish freezing before it reaches the ground, eventually the drop turns into an ice pellet. That's known as sleet.

But if the layer of sub-freezing air is shallow, the drop only has enough time to reach the liquid "supercooled" state.

And when a supercooled drop hits the ground, it instantly freezes to any surface it touches -- thus the term, "freezing rain."

LEARN: What is an ice storm?

As more freezing rain falls, a glaze of ice will form on everything -- sidewalks, roads, cars, trees, power lines, homes -- that will only get thicker as the storm continues.

2) Freezing rain has caused some of the nation's worst crashes

Even a thin glaze of freezing rain can erase all traction on pavement, leading to dozens to hundreds of crashes as cars and trucks careen out of control.

"Freezing rain is the worst," the National Weather Service says. "(It's) more dangerous than snow, as ice can form on pavement."

Just last year, six people were killed in Fort Worth when an ice storm led to a 135-vehicle pileup on Interstate 35W.

According to the Federal Highway Administration, Over 1,300 people are killed on snowy or icy pavement each year.

3) It only takes 1/2" of ice to cause crippling effects

It might not seem like much, but even just a quarter inch of ice can be disruptive to a region with numerous power outages and some tree damage, along with slick roads.

And once ice thickness reaches just a half inch, it will have crippling effects on an area. Widespread power outages and tree falls will occur as branches and power lines succumb to the weight of all that ice.

LEARN: How much ice is needed to knock out power, damage trees?

4) Power outages have lasted days to weeks in the greatest storms

Unlike a wind storm where some trees and power lines might topple, but other parts of the power grid may avoid damage, a major ice storm can wipe out a majority of power lines across the region.

LEARN: What to do – and what not to do – for removing ice from your windshield

An ice storm in Dec. 2007 that struck across the Midwest left wide swaths of Kansas under 1-2 inches of ice, with some spots seeing 2-4 inches of ice accretion, according to the National Weather Service in Wichita.

"Many areas were without power for 1-2 weeks!" the National Weather Service wrote. "Damage to the electrical infrastructure alone was estimated at $136.2 million making this the costliest ice storm in Kansas history."

5) Seeing Pink? Watch out for the Skating Rink

On weather forecast maps and on most Doppler Radar screens, freezing rain or sleet is denoted as a pink or reddish layer, frequently sandwiched between an area of snow in blue and rain in green.

6) Look for freezing rain where warm and cold air masses collide

Freezing rain and sleet are most commonly found around the boundary between the warmer air ahead of the approaching winter storm and the colder air behind it.  It's especially common on northern sides of warm fronts.

That's where you can get the warm air nudged in between the snowy cloud base and cold air trapped on the ground.

7) Ice "accretes", it doesn’t' accumulate

You might hear meteorologists or emergency managers refer to ice "accretions" when describing amounts of freezing rain.

While snow and rain totals are communicated as accumulations, ice accretes -- as in the ice grows in layers as more freezing rain falls, as opposed to collecting on a surface or in a container like snow and ice. 

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