How to Measure Ice Accumulation (Because It’s Different From Snow)

Last week, Winter Storm Landon slowly worked its way across the country, causing frigid temperatures, heavy snowfall, and slippery roads. And thanks to the freezing rain that fell alongside the snow, weather reports included accumulation totals for ice as well as snow.

While measuring snow depth is relatively straightforward, keeping track of how much ice is coating a surface is more complex. Here’s what to know.

What is ice accumulation?

Typically, when people talk about ice accumulation, they’re referring to ice that has formed as a direct result of freezing rain and/or sleet—not ice that has thickened as surrounding snow has melted and then refrozen. According to the National Weather Service (NWS), ice accumulation of more than 1/4″ is cause for concern, as that’s enough to take down trees and utility lines (causing power outages) and make walking and driving dangerous.

Why is it harder to accurately measure ice accumulation?

Basically, it comes down to the fact that freezing rain is tricky. That’s because it falls as a liquid, but then freezes as soon as it comes in contact with the ground or another surface, forming an ice glaze.

But that glaze doesn’t coat surfaces evenly, thanks to wind and gravity, which causes the rain to travel to the underside of an object before freezing, the NWS explains. This means that one side will have a thicker coating of ice than the other, making measuring accumulation difficult.

How to measure ice accumulation

Here’s a method the NWS suggests for measuring ice accumulation at home using a ruler:

1. Find an object that is covered in ice and out in the open (like a small tree branch from the middle of a yard).
2. Position yourself so you can see both the thickest and thinnest parts of the ice coating the object from one side to the other.
3. Measure the thickest part of the ice with a ruler, from the edge of the object to the edge of the ice. Record that value (on your phone, a piece of paper, etc).
4. Then measure the thinnest part of the ice the same way (from the edge of the object to the edge of the ice) and record it.
5. Add the two measurements together and then divide by two to get the estimated total ice accumulation.

And it should go without saying, but please be careful when moving around in an area covered in ice.