Today’s weather word of the day in Iowa City is Graupel.
Graupel is a winter phenomenon often mistaken for hail or sleet, but it’s actually quite different. Graupel is the result of super-cooled droplets of water freezing to the surface of a snowflake. Unlike a hailstone, they are not truly round in shape, they’re more like little globs of lumpy ice and are usually only 2-5 mm in size. The easy way to tell graupel from hail is to try and pick it up. Hailstones are hard while graupel pellets are soft and mushy. This is a handful of graupel.
How is graupel different from hail or sleet? Read on.
Hail is a sphere of ice that falls from the clouds during a thunderstorm in the warmer seasons. Hail is usually 5mm to 15 cm in size (about 1/4 inch to 6 inches), and is formed inside thunderstorms with significant updrafts. Hailstones are made of many hard uniform layers of ice that rise and fall inside the clouds until they weigh to much for the updrafts to keep aloft. Hail rarely forms in the winter.
Sleet, which resembles hail, forms during winter storms when a snowflake passes through a small warmer layer of air after forming. The flake partially melts, then refreezes into a droplet shape before it reaches the ground. Sleet often falls in conjunction with very cold rain.
Freezing rain or Glaze Ice is super-cooled rain that freezes on contact with a surface that is at or below 32 degrees.
Here’s one last fun weather word: Rime. Rime is what is created when the water droplets in fog freeze when they come in contact with something very cold – like a car windshield. Rime comes in two types – Hard Rime which forms on the windward side of objects during moderate to high winds or Soft Rime which forms on all sides of an object when there is little or no wind.
The Snowflake: Winter’s Frozen Artistry by Kenneth Libbrecht
Thunder & Lightening: weather past, present, future by Lauren Redniss.
Restless skies: the ultimate weather book by Paul Douglas