We got lots of reports on Thursday from viewers saying hail was falling in their yards, covering their sidewalks and decks and cars. What we saw Thursday was not actually hail. Its a wintry precipitation type known as graupel.
Hail occurs when raindrops are transported upward into subfreezing air by skyward-moving winds called updrafts. As the raindrop reaches air that is below freezing, it freezes solid. Other raindrops can be deposited on the original hailstone, making it larger and larger, depending on the strength of the updrafts. The bottom line: Hail is solid ice.
Graupel on the other hand is not solid ice. It is made up of dozens of snow flakes that are caught in a strong up draft and transported aloft. These snowflakes are "rolled together" into what resembles little styrofoam balls. Graupel looks like little mini snowballs.
Hail starts out as rain drops and is a solid ball of ice. Graupel starts out as snowflakes and is not solid. In fact, when graupel hits the ground, it often explodes into smaller pieces.
Graupel is common in early season lake effect snow bands. It tells us that there is a strong updraft in the heavy lake effect snow band. When you see graupel, you may also hear thunder.
The same strong updraft winds that produce graupel will, often, produce thunder and lightning. In fact, if you hear thunder in a snow squall, there is always graupel falling nearby.