Weather Whys; Rime Ice

This is weather wise. On some winter mornings, the mountains might look gray and somewhat fuzzy, like heaps of dust balls on the horizon. That's because the trees on the hillside are coated with a substance called rhyme ice. You can find that same thing year round in the freezer compartment of any old-style refrigerator. The depositing of rhyme ice on a surface is called rhyming, and it occurs when tiny droplets of water hit a cold surface and freeze before they can spread out. That leaves a rough lumpy coating of ice. Rhyming is a common occurrence in hilly areas because the tops of the mountains are often shrouded in clouds and the winter air can chill the ground and trees to sub-freezing levels, which are just right for the development of ice. This sort of icing can also be a major problem for aircraft, since planes can ice up fairly quickly as they fly through clouds that are composed of extra cold water droplets. If it's rhyming that occurs, the rough texture of the ice disrupts the smooth air flow over

the wings. In extreme cases, that can greatly change the aerodynamics of a plane and make flying much more difficult. But in general, rhyme ice is relatively light and porous. In fact, it's much lighter and less dense than a solid sheet of ice, so aircraft de-icing mechanisms can usually take care of it. Rhyme ice can be strange looking on the mountain sides, annoying in your freezer and even dangerous on an airplane. But it's also thought to be an important contributor to the precipitation process and to the formation of hail. Whether wise, our writer is Christine Harbour, our editor is Brian Walkie, and our executive producer is Karen Holt. Whether wise is made possible by a grant from the National Science Foundation. But whether wise, I'm Drew Barlow.