Residents Baffled by Graupel

Residents Baffled by Graupel
Residents Baffled by Graupel

It’s not snow.  It’s not hail.  It’s something in-between, and it’s been falling all over the Inland Northwest this week.  It’s GRAUPEL.   Most folks confuse graupel with hail or snow, but there is a difference.

The American Meteorological Society Glossarydefines graupel like this: Heavily rimed snow particles, often called snow pellets.  Hail, on the other hand, is defined like this: Precipitation in the form of balls or irregular lumps of ICE always produced by convective clouds, nearly always cumulonimbus.

Graupel occurs on days when the temperature at the surface is above freezing, but there is very cold air aloft, creating instability (like the weather we have had this week).  Graupel is essentially snowflakes that become rounded into balls or pellets when supercooled water droplets coat, or rime them.  The pellets are cloudy or white, and soft.

Hail, on the other hand, is a pellet of ice, not snow.  It is formed in a thunderstorm updraft where the rising, warm, moist air transports ice fragments back and forth between the freezing and non-freezing layer of the atmosphere.  Layers of ice accumulating on the hail develop, and when the hail stones become heavy enough to overcome the force of the updraft, they fall to the ground.  The stronger the updrafts, the larger the hail stone. 

Another way to tell the difference: graupel is typically white like snow, while hail is more clear/transparentlike ice.  Graupel is soft, and you can crush it with your fingers, while hail is hard.  If you see graupel or hail at your house, I would love to know about it.  Send me an e-mail: krisc@kxly.com