The experience with graupel is that it is a combination of a large snowflake and a small hailstone. They fall faster than snowflakes but a little slower than hail. Sometime graupel is called “soft hail”. It forms by large snowflakes that are suspended aloft that grow by supercooled water drops freezing on the snow. This allows graupel to have a bright white color and a faster fall rate than snow. This type of storm is more common in higher elevation regions since there is an absence or a significant reduction in the amount of warm air the precipitation needs to falls through to reach the surface. In a lower elevation location, it is more likely the graupel will melt into heavy rain before reaching the surface. Relatively strong lifting is needed to form graupel, thus when it does form, many times a heavy shower of graupel will be experienced. Graupel can accumulate on the ground in a similar fashion to heavy snow. Several inches can fall in an hour especially if the storm is slow moving. It can look like several inches of snow occurred. Unlike snow though, it is not good for making snowballs and is denser than snow. In a freak graupel storm, a convective storm will form in an environment that supports frozen precipitation that can reach the surface. Heavy precipitation forms in the updraft. The strong updraft and cold temperatures allow for a heavy winter precipitation to develop aloft. Instead of the heavy rain that a thunderstorm would have, heavy graupel falls to the surface. It can accumulate quickly. In the bigger storms, snow plows will be needed to remove the accumulation from roadways. |