Three things are needed to make a large snowstorm or blizzard.

1. Cold air (below freezing) is needed to make snow.

For snow to fall to the ground, the temperature must be cold both up in the clouds where snowflakes form, and down at ground level. If the air near ground level is too warm, the snow will melt on its way down, changing to rain or freezing rain.

2. Moisture is needed to form clouds and precipitation.

Moisture in the air is called water vapor. Air blowing across a body of water, such as a large lake or the ocean, is an excellent source of water vapor. As wind moves air over the water, some water evaporates from the surface, putting vapor into the air. This is how “lake effect snowstorms” and “Nor’easters” pick up so much moisture. However, cold air is not able to hold much water vapor. In fact, very cold air does not make very much snow.

3. Moist air needs to rise, over very cold air, making clouds and snow.

There are two ways that moist air might rise over cold air. Winds pull cold air toward the equator from the poles and bring warmer, moist air toward the poles from the equator. When warm air and cold air are brought together, a front is formed and snow can form. Warm air can also rise to form clouds and blizzard snows as it flows up a mountainside.

https://scied.ucar.edu/webweather/winter-storms/what-blizzard-needs

More About Blizzards...

Snow whirling around in wind blowing faster than highway speed limits makes the whole world look white. Imagine snow so deep that second graders can’t see over the top of it. The wind and the snow may cause a power outage and collapse roofs. That’s what you can expect from a blizzard.

The National Weather Service defines a blizzard as a storm with large amounts of snow or blowing snow, winds greater than 35 mph (56 kph), and visibility of less than ¼ mile (0.4 km) for at least three hours. Some blizzards, called ground blizzards, have no falling snow. Instead, snow that had fallen before the blizzard is blown around or drifts in a way to create these conditions.

Conditions for a blizzard usually will build up on the northwest side of a powerful storm system. The storm produces ample snow while strong winds develop because of a difference in pressure between the low pressure of the storm and the high pressure beyond the storm.

In the United States, blizzards are common in the upper Midwest and the Great Plains but occur in most areas of the country except for the Gulf Coast and the California coast. Blizzards can occur all over the world, even in the tropics where it is cold on high altitude mountaintops.

Conditions of a blizzard can be severe. Travel becomes dangerous when the blowing snow causes whiteout conditions and sky and ground look white. Roads can be partially or fully blocked by snowdrifts – piles of snow formed by the wind. Many times cold temperatures that can cause frostbite or hypothermia are part of a blizzard and can last for days after the storm has ended.

https://scied.ucar.edu/shortcontent/blizzards

fortune.com

The East Coast Is Bracing for a Winter ‘Bomb Cyclone.’ What Is That?

By Chris Morris Updated: January 3, 2018 11:19 AM ET|Jan. 3rd, 2018

Weather terminology can be a bit scary at times. Terms like “arctic blast” and “typhoon” create some disturbing mental images. But as East Coast residents in the United States prepare for winter storm Grayson this week—the National Weather Service says the storm will bring strong, damaging winds and snow—they are hearing a new term and it might be the most terrifying of all: “Bomb Cyclone.”

Even in the often-hyperbolic field of weather prediction, that’s an eye-catching name, but what is a bomb cyclone? And how bad will it be if you’re in it’s path?

The answer, as with so many things when it comes to winter weather, is: It depends. A bomb cyclone is, essentially, a powerful low-pressure system that rapidly intensifies. If that sounds a lot like a hurricane, you’re not too far off. The ‘bomb’ part of the name refers to the phenomenon when the pressure inside a storm cell falls so quickly that it gives the storm explosive strength.

Technically, the term bomb cyclone comes from the scientific term “bombogenesis,” which is a storm that drops 24 millibars of pressure over 24 hours. And what forecasters are worried about with this one is the pressure levels could be on the same level as Hurricane Sandy. (Researchers say climate change can be blamed for these sorts of events.)

That means the potential for hurricane or tropical storm force winds is present—though the damage likely won’t be as bad as it was with Sandy. And it’s possible that this could be much ado about nothing, since slight shifts in the system’s placement could make huge differences in snowfall.

One thing’s clear, though. It’s going to be brutally cold no matter what happens with this storm. A new arctic blast is on its way down from Canada, so whether this bomb cyclone results in high winds, heavy snow, or people complaining the weather weenies blew the call again, you’re going to want to stay inside. In addition to hurricane-force winds and snow or sleet, temperatures could also drop 20 to 40 degrees below normal.

What is bombogenesis?

Bombogenesis is a popular term that describes a midlatitude cyclone that rapidly intensifies.

Fourteen of 20 hurricane-force wind events underwent bombogenesis in the North Atlantic during the first two months of 2014. This unusual activity can be seen in wind speed data from the period. In this image, blues indicate areas with wind speeds that are faster than the 30-year historical average (1981-2010).

Bombogenesis, a popular term used by meteorologists, occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibarsover 24 hours. A millibar measures atmospheric pressure. This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone.