What Causes a Blizzard?

Two feet of snow fell overnight. Was that a blizzard? Not always!

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The quick answer

A blizzard is not about how much snow falls. It is about wind. When strong wind fills the air with snow so thickly that you can barely see, and it keeps going for hours, that is a blizzard.

How it works

Start with snow
The snow can be falling from the clouds, or it can be loose, powdery snow that is already lying on the ground.
Add strong wind
Wind grabs that snow and throws it sideways. The air fills up with flying flakes.
Lose the view
With that much snow in the air, things disappear. The mailbox across the street, the stop sign, the bus. When everything turns white and you cannot tell ground from sky, it is called a whiteout.
Keep it going
A quick snowy gust does not count. Forecasters only call it a blizzard when the wind and the terrible visibility last for hours.

Thunder Tidbits

The official United States blizzard rules: winds of 35 miles per hour or more, visibility of a quarter mile or less, lasting at least three hours.
Notice what is missing from those rules: there is no minimum amount of snow.
A storm can drop two feet of snow and still not be a blizzard if the wind stays calm.

Words to know

Visibility: How far you can see.
Whiteout: Blowing snow so thick that everything looks white in every direction.
Ground blizzard: A blizzard made from old snow being blown around. No new snow has to fall, and the sky above can even be clear.
Wind chill: How cold the air feels on your skin once the wind is added.

Try it: Ground blizzard in a jar

Put a spoonful of glitter or fine salt in a clear jar of water and let it settle to the bottom. That is yesterday's snow lying on the ground. Now swirl the jar. Nothing new was added, but suddenly you cannot see through it. That is a ground blizzard.

Stay safe

In a blizzard the safest place is indoors. It is easy to get lost just a few steps from your own door. Families who live in snowy places keep blankets, snacks, water and a flashlight in the car all winter.