Malary Hathcox of Victor sent in photos of rime ice coating the trees outside her home and wanted an explanation as to what is the difference between rime ice and hoarfrost. Watch the video above as Meteorologist Mitchel Coombs describes what makes these types of ice different.
Both are common to see across western Montana during the wintertime, especially on frigid mornings. Both rime ice and hoarfrost develop in the presence of excess moisture near the surface, often on objects of smaller diameter, such as tree branches, wires, plant stems or leaf edges.
Rime ice and hoarfrost look similar and can be a challenge to differentiate, even to meteorologists. The differences between the two involve the state of the water molecule before it freezes, as well as the water source itself.
With rime ice, supercooled water droplets from freezing fog transition from liquid to solid upon direct contact with a surface at or below 32 degrees.
There are two types of rime ice. Hard rime develops at colder temperatures and stronger winds that can coat trees solid in ice. There is also have the soft rime which develops when winds are light and creates needlelike crystals.
Hoarfrost, on the other hand, develops on cold, clear nights when gas water vapor transitions directly to solid ice crystals through the process of direct deposition. Snow on the ground can release moisture that promotes hoarfrost growth.
Whether you see rime ice or hoarfrost, they can both produce beautiful winter scenery, especially when the sun is shining brightly. However, be aware the ice can create slick roads and sidewalks as well as increase avalanche dangers in the backcountry.
If you have photos of rime ice or hoarfrost, send those to nbcmontana.com/chimein. Thank you, Malary, for your question. If you have weather or science related questions you would like answered, email me at mrcoombs@sbgtv.com or reach out on Twitter and Facebook.