Fall or Winter?

Mt Jacskon with the Josiah Bartlett 8th grade. Photo: Nancy Ritger

On a recent trip with 8th grade students from Josiah Bartlett School we encountered a mix of seasons. Ice feathers coated the vegetation on Mt Jackson yet down in the valleys the sun revealed a splash of color at lower elevations.

Photo: Nancy Ritger; taken from the summit of Mt Jackson 10/1/09

The Autumnal Equinox signaled the official beginning of Fall. Celebrated only 2 weeks ago, yet here we are in the middle of wild weather more typical of winter.

A phenomenon called rime ice forms on trees and sign posts at treeline when the conditions are just right including freezing temperatures, wind, moisture and something to collect on. Super cooled water droplets suspended in the clouds freeze instantly when they hit a solid object. The water droplets are very small and their surface tension is high enough for them to remain liquid well beneath the freezing temperature of water. In conditions below 32 degrees as a cloud sweeps by an object the droplets freeze and the rime ice builds in the direction of the wind forming long feather-like structures of ice crystals.
Rime ice on Balsam fir. Photo: Nancy Ritger

Trees that are exposed to rime ice conditions are commonly damaged by the growth of rime ice structures on their branches. Ice encrusted branches cannot bend with the wind and as a result they are often torn off the tree leaving only the branches protected by the trunk. This produces "flag trees" - trees that have lost branches on one side with the remaining branches make the tree look like a flagpole, with a flag , flying in the wind. In areas where the wind is stronger - at higher elevations - rime ice shears off upright growth of spruce and balsam fir trees thus causing the trees to grow horizontally along the ground. Therefore rime ice is a major factor in determining the elevation of treeline.

As we descended the summit we saw less and less rime ice until the temperature warmed a few degrees and only the dripping from the trees reminded us of any moisture in the air. In a few short miles we experienced the change from fall to winter and then back to fall again. Not only does the weather change often in the mountains but we find the seasons can change just as fast.