100+ mph, Rime and Snow on the Summit!

By Alexis George

Winter-like conditions have been in full swing at Mount Washington since I first arrived on the summit last week. Summit staff enjoyed high winds on Saturday, October 12th, when winds gusted to 121 mph at the summit. Several inches of snow have fallen over the past few days, with the summit receiving 4 more inches of new snowfall just yesterday. Summit staff members took advantage of the recent snowfall and went sledding at the summit recently!

The summit also commonly sees rime ice developing when below freezing temperatures and strong winds are present. Specifically, rime icing is a phenomenon that occurs when a location is in the clouds (fog) and the air temperature at said location is below freezing. The cloud (fog) is made up of millions of water drops that are so tiny, and all these droplets need to turn into ice is something to come in contact with that is below freezing. Thus, this impact causes the supercooled water droplets to turn into ice, and, as the drops continue to come in contact with a structure or surface, the ice builds up in the direction. Mount Washington spends 60% of the year in the fog and has a yearly temperature average of 27 degrees. Hence, this means plenty of rime typically develops at the summit of Mount Washington. It is actually possible that the summit of Mount Washington can see riming rates of 9 inches or more in an hour!

Rime ice is one of the most common weather phenomena up here on the summit and is one of the biggest reasons why Mount Washington Observatory is staffed 24/7. Thus, it was a common occurrence for all the weather observers this past week to suit up, climb a series of ladders to get to the top of the tower, and knock the ice accumulating on the instruments with a mallet.

Deicing on the summit this past February.

To learn more about rime ice, check out the video below as MWOBS Director of Education Brian Fitzgerald and Meteorologist Ryan Knapp discuss the science behind how it forms, and what implications the phenomenon has on summit instrumentation.