What defines a blizzard? Heavy snow and high winds expected to sweep across country.

Anna Kaufman, USA TODAY
·3 min read
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An intense blizzard is set to hit large swaths of the country before Christmas — shaping up to be a possible bomb cyclone, forecasters for the Weather Channel report. Heavy snows, strong winds and low temperatures are expected to affect the Central and Northern Plains, as well as the Upper Midwest and Great Lakes this week.

The National Weather Service issued a winter storm watch on Tuesday for upwards of 40 million Americans throughout the north central U.S., including Chicago. The storm system, which forecasters for the National Weather Service sat will develop Wednesday night and gain strength as it travels toward the Great Lakes, will create blizzard conditions by the end of the week, dumping snow throughout the Midwest and bringing high winds and frigid temperatures.

Here's everything you need to know about blizzard conditions.

Stay up to date on winter storm Elliott: Pre-Christmas blizzard expected to wallop northern US could strengthen into a bomb cyclone

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What is considered a blizzard?

The National Weather Service defines a blizzard as blowing or falling snow with winds of at least 35 miles per hour. The result is reduced visibility to a quarter of a mile or less for three hours or more.

If there is snow already on the ground and high winds are disrupting it and creating low visibility as a result, that is called a ground blizzard.

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What are blizzard conditions?

A blizzard is characterized by falling temperatures, heavy snowfall and high winds — a trifecta of conditions which make for low visibility.

With a pre-Christmas blizzard expected this week in the U.S., low visibility can make ground and air travel unsafe, creating a headache for holiday travelers.

"There could be massive delays flying in and out of the East Coast and those could trickle even to the West Coast, so places that aren't (getting the storm directly) could see travel impacts rippling across the country,” AccuWeather senior meteorologist Adam Douty told USA TODAY. .

High winds can also topple trees and down power lines, causing outages that can leave some homes without heat.

What is wind chill? Understanding the wind chill index and how it's calculated

How to prepare for a blizzard at home?

The National Weather Service recommends homes have these items to prepare for blizzards, which can cause outages and leave people trapped in their homes:

  • Medications, infant formula, any specialty health items you might need

  • Portable radio with batteries

  • Warm clothing and blankets

  • Matches

  • Shovel/snowblower

  • Flashlights with batteries

  • Fully charged cell phone

  • Firewood

  • First aid kit

The National Weather service advises folks keep these kitchen items in supply:

  • Canned fruits and veggies (make sure you have a can opener)

  • High energy foods like chips, crackers, nuts, fruit bars

  • Cookies and hard candy

  • Soup

  • Cereal and toaster pastries (you may have to eat these without the toaster)

  • Bread and condiments

  • Bottled water

  • MRES: Meals Ready to Eat

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What is a bomb cyclone?

A bomb cyclone, which is created through a process known as bombogenesis, is a severe winter storm.

Essentially a "winter hurricane," USA Today's Doyle Rice writes, a bomb cyclone occurs when a cyclone at mid-latitude rapidly intensifies, and its central barometric pressure drops at least 24 millibars in 24 hours. The lower the pressure of a storm, the higher its intensity, The Weather Channel reports.

Many of the most intense winter storms to batter the country's northern coast have been bomb cyclones.

What three things cause a blizzard?

  • Frigid temperatures

  • High winds

  • Heavy snowfall

When temperatures are low enough for snow, and that snow is blown by winds over 35 miles an hour, a blizzard results, creating low visibility.

This article originally appeared on USA TODAY: What is a blizzard? Breaking down winter storm conditions