FORMATION

In winter, when cooler dense air from the poles meets the warmer moist air of the tropics along the Earth's polar front, it may trigger snowfall. If a period of of high pressure occurs, forst and ice are lickely.

Three things are needed for a blizzard to form:

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.

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. Warm, rising air is needed to form clouds and cause precipitation.

For a blizzard to form, warm air must rise over cold air. There are two ways that this may happen. Winds pull cold air toward the equator from the poles and bring warm air toward the poles from the equator. When warm air and cold air are brought together, a front is formed and precipitation occurs. Warm air can also rise to form clouds and blizzard snows as it flows up a mountainside.

Snowflakes:

Snowflakes are made of ice crystals. Each snowflake is made of as many as 200 ice crystals. Some snow crystals are symmetrical, like the type that you cut from paper. They form a hexagonal shape because that is how water molecules organize themselves as they freeze. Others are small and irregularly shaped. If they spin like tops as they fall to the ground, they may be perfectly symmetrical when they hit the Earth. But if they fall sideways, they will end up lopsided.

One particularly powerful type of blizzard forms during a nor’easter. These cyclonic storms strike the Atlantic coast, and their name comes from how the counterclockwise rotation pushes strong winds onto land from the northeast quadrant of the storm. When a nor’easter forms in the depths of winter, the rotation can pull warm, moist air from southern waters, wrapping it around the storm’s eye where it meets the cold, polar air from the north. This clash of temperatures and high moisture levels can create the perfect conditions for a blizzard, and these storms can be as intense as a hurricane.