Freezing rain vs. sleet vs. snow: why it can rain and still ice

Whether you get snow, sleet or freezing rain is decided by the layers of air above you, not by the temperature where you're standing. Of the three, freezing rain is the dangerous one: it falls as rain and turns to ice the moment it lands.

It almost always starts as snow

Most winter precipitation begins as snow, high in the cloud. What reaches the ground depends on what that snow falls through on the way down:

• Cold all the way down: it stays snow.
• A warm layer partway down, then a deep cold layer below it: the snow melts into rain, then refreezes into small ice pellets before it lands. That's sleet.
• A warm layer, then only a thin cold layer at the ground: the snow melts into rain and doesn't have time to refreeze. The drops land as liquid and freeze the moment they touch anything at or below freezing. That's freezing rain.

So a warm layer you can't feel, maybe a mile up, can decide your whole day.

How to tell them apart

• Snow is flakes.
• Sleet is little ice pellets that bounce when they hit the ground or your windshield. It piles up like coarse sand.
• Freezing rain looks and sounds like ordinary rain. You find out it's freezing rain when everything it touches is coated in clear ice: cars, trees, steps, power lines.

Sleet isn't hail. Sleet is a winter thing, made from melted snow. Hail forms inside thunderstorms, usually in spring and summer, and can be much larger.

Why freezing rain is the dangerous one

Sleet is slippery, but freezing rain builds a glaze of ice on everything, and the ice keeps getting heavier as long as the rain falls. Even a thin coat makes roads and sidewalks extremely dangerous. When around a quarter inch of ice or more is expected, the National Weather Service issues an Ice Storm Warning: at that weight, tree limbs and power lines can snap, and power can be out for days.

Bridges and overpasses freeze before other roads, because cold air reaches them from above and below. A road that's only wet can be icy on the bridge.

Why the forecast says "wintry mix"

The warm layer that makes the difference may be only a degree or two above freezing, and only a few hundred feet thick. A small change in it moves the line between snow, sleet and freezing rain, sometimes by tens of miles. That's why a forecast can say "wintry mix", and why it can change the day before. Check the latest forecast, not yesterday's. Your town's or county's page on Atmostorm shows the next three days, and names freezing rain or sleet on the days it's the most likely type.

What to do

• Winter Weather Advisory: snow or ice below warning level, but roads can still be slick. Slow down and allow extra time.
• Ice Storm Warning: ice will coat roads and power lines. Avoid travel, and expect outages: charge devices now.
• Treat every bridge and overpass as icy until you know it isn't.

Get warnings sends Ice Storm Warnings for your place by email, with no account, and to your phone if you also tick the box for winter storm and other warnings. Advisories aren't sent; you'll find them on the map and your town's page.

Watch the short explainer on our YouTube channel.