Mountain Weather Background

The basics of mountain weather include increased wind speeds, decreased temperatures, and increased precipitation with elevation. As for the White Mountains, there are a few other phenomenan that give us particularly harsh weather.

1. We lie directly in the path of 3 out of 12 of the major storm tracks that cross our country- in shear quantity we have more potential storms than most other locations
2. Rime Ice - freezing fog! Water can supercool itself down to –38F and remain in the liquid form as long as it has nothing to condense upon. Once this supercooled liquid touches something, however, it will instantaneously freeze to form rime ice. Because of New England’s high humidity level, rime ice is a common feature of the winter landscape and plays a primary role in determining tree line. Rime ice builds up on branches and foliage, only to break off in high winds, stripping trees of their vegetation and making life more difficult in the harsh wintry conditions.
3. Alpine zone- Beginning at about 4000 feet, the White Mountains’ alpine zone is one of the lowest in the world. Heavy rime ice, extreme winds, and a short growing season prevent trees from growing larger than shrub size in the alpine zone.
4. Lightning – Thunderstorms need a supply of warm humid unstable air and something to give an initial upward shove, such as air being forced up over the mountains. Lightning can be hazardous to humans traveling on exposed ridges.

As wind runs into a mountain it flows up the side until it reaches the top. It cannot continue to flow upwards because wind flowing above the mountain forces it back down. When the rising air reaches the top of the mountain, it must all funnel through a small area just above the peak. To make a large amount of air flow through a small space, the wind speed must increase. This same action happens in rivers; When the river is wide, it flows slowly, but as it narrows, the water speeds up. This is because the same amount of water needs to fit through a smaller space.  This principle of fluid dynamics explains high wind speeds on mountain tops and high flow rates in river narrows.