If you recently saw ice pellets bouncing when they hit the ground, you weren’t imaging things.

Almost all precipitation forms in the atmosphere as snowflakes, according to Adnan Akyuz, professor of climatological practice at North Dakota State University and North Dakota’s state climatologist.

As the snowflakes fall through an atmospheric layer that is warm enough to melt the snow, the snowflakes become raindrops. If the raindrops fall through another layer that is at or below freezing temperatures before reaching the ground and the layer is deep enough to freeze the raindrops, tiny ice pellets called sleet will form. Usually, these ice pellets are transparent with a diameter of 0.02 inch or less.

“They bounce when they fall to the ground, car hood or other surfaces because they are hard, yet light enough to defy gravity for a brief moment after the collision,” Akyuz says.

He warns that North Dakotans could be seeing more rainfall in the winter because winters have been getting warmer at a faster rate in North Dakota than in any other state in the U.S.

“Unfortunately, liquid precipitation in winter poses a hazard that we are not used to: freezing rain,” he notes.

Freezing rain occurs if the layer at or below freezing temperatures is not deep enough to give the raindrops time to freeze. The rain droplets will strike the Earth as liquid, usually as supercooled liquid droplets. These droplets will freeze almost immediately upon contact with cold objects, such as cars, streets or trees. These droplets form a thin veneer of ice called freezing rain or freezing drizzle, depending on the size of the droplets.

“Driving through this type of precipitation brings an unfamiliar challenge to North Dakota drivers,” Akyuz says. “We all need to adapt to the change and give ourselves some time to get to know about the weather that surrounds us.”

NDSU Agriculture Communication - Nov. 23, 2016