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

Photo: Nagel Photography (Shutterstock)

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.