What is graupel? How it is different from sleet or hail?

Graupel, hail, sleet, freezing rain and snow all form differently on the way down from a cloud. Here's how to tell one from another.

Precipitation can take a variety of forms with each one posing its own hazards.

Much of the precipitation that falls throughout the year begins as snowflakes high in the clouds. The snowflakes form as air rises, cools, and condenses, usually around an area of low pressure.

Whether or not precipitation remains snow or transitions to rain, freezing rain, sleet, hail or graupel by the time it reaches the ground hinges on the temperature fluctuations the snowflakes may encounter as they travel through the layers of the atmosphere.

Here is an overview of five different types of precipitation, how they form and what hazards they can bring:

Sleet vs. freezing rain

Sleet and freezing rain occur by a similar process, but are different forms of precipitation. Both are most common in the winter.

Sleet occurs when snowflakes melt into a raindrop in a wedge of warm air well above the ground and then refreeze in a layer of freezing air just above the surface. This results in frozen raindrops, that are hard, small, and clear-colored. Sleet is also called ice pellets.

Freezing rain occurs when the wedge of warm air aloft is much thicker, allowing the raindrop to survive until it comes in contact with the cold ground. A coating of ice forms on whatever the raindrops contact.

"Freezing rain is by far the most dangerous because it forms a solid sheet of ice, as opposed to sleet that just has small ice pellets that quickly bounce off of the surface," AccuWeather Senior Meteorologist Brett Anderson said. "Actually, sleet can even provide a little bit of traction for drivers, as opposed to the obvious dangers of a solid sheet of ice that forms from freezing rain."

The additional danger with freezing rain is the potential for ice to accumulate on trees and power lines, possibly leading to damage and power outages.

What is graupel?

While snow, sleet, and freezing rain are familiar precipitation types to most people, one that may be lesser known is graupel, also known as snow pellets.

Graupel forms when a water droplet gets lifted and supercooled, freezing onto existing snowflake, coating them with ice. It can be the same size as sleet but is typically white and opaque.

Unlike hail or sleet, graupel is soft and can be crushed easily in your hand, and is sometimes called "soft hail." It is also usually smaller than hail, with a diameter of around 0.08-0.2 inches.

Graupel is most common in the spring and fall seasons.

Hail

Hail is a chunk of ice that can fall during thunderstorms. Unlike snow, sleet, freezing rain, and graupel, which occur in colder weather, hail is most common in warm conditions, during spring and summer.

The size of the ice can vary based on the strength of the thunderstorm, with the largest hail comparable to the size of a softball.

The larger the hail, the greater the risk of damage to cars, roofs, siding and crops.

Any livestock or person that is outside when a hailstorm strikes can be at risk of life-threatening injuries.

In the United States, the largest hailstorms typically occur in the High Plains.

Snow

When the temperature between the ground and the clouds remains at or below the freezing mark (32 degrees Fahrenheit), precipitation will fall as snow.

It is possible for snow to fall when temperatures are above 32, as long as the layer of above-freezing air near the surface is rather shallow, not allowing the snowflakes to melt.

When the surface temperature is near or just above 32, snow can be heavy and wet. While this type of snow is great for making snowmen or snowballs, it is very difficult to remove from driveways, sidewalks, and cars.

Dry, powdery snow that is easy to remove but can cause blowing and drifting problems is more likely when the air is drier and colder.

Regardless of the type of snow, motorists can experience slippery and dangerous travel, especially if the ground is cold enough for the snow to stick immediately.

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