PORTRAITS OF RIME FROST
CRYSTALS

 [“Rime” Rhymes With Time]

WHAT IS RIME FROST?
Rime frost forms in mountains on the leading edge of cold vegetation (tree branches, stems, and ground plants), leaving directional wind-swept ice formations on their surface. These formations are hard to the touch and not easy to dislodge.

From a distance these frost formations look like snow but it is not snow. Only the forest foliage is white against the dark brown leafy autumn ground around and under it.

Rime frost is found only at the higher elevations, and it is specifically associated with a freezing moist foggy cold snap that is accompanied by gusty or gale-force winds. The freezing winds blow super-cooled dew droplets [in the fog] over exposed vegetation, instantly coating them with directional (and beautiful!) ice crystals.

'Directional' is a key word: the crystals form in a fascinating windward direction (the direction that the wind is blowing from.) The more gale-force the winds, the more distinct the directional patterns.

We had just such conditions not long ago in the Smokies.

The mountains had been shrouded in dense, low-hanging damp fog for days when temperatures one night suddenly plummeted into the mid-teens during gale-wind conditions. The next morning I found portraits of rime frost everywhere I looked! These images illustrate the diverse ways that rime crystals attach themselves to exposed objects in nature.

Gallery I

Gallery II