Weather in the mountains is complex.  The peaks and valleys of the terrain plays a significant role in the large variability of the weather over a relatively small scale.  

For example, mountains can act as rain shadows: moist air that rises up the side of mountain that faces the prevailing winds results in significant amounts of rain and snow while the air that reached the other side is much drier as all the moisture has been removed.   

It is important to keep the complexity of mountain weather in mind as we try to understand mountain climate, which is the long-term average weather, and how mountain plants and animals are responding to the larger geographical scale changes in temperature and precipitation from human caused climate change. 

The basics of Mountain Weather                                 Mount Washington Examples

Mountains tend to be wetter:                                       Annual Average Precipitation
   Moist air that collides with the                                             Summit      98.96”
   mountain is pushed upward, cools                                       Valley        46.08”
   and condenses to form clouds. 

LOCATION	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.
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.
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.
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.