Last week, I heard a great talk at the AMC Boston Winter Hiking Program given by Larry Takiff on Mountain Weather and Avalanche Awareness. Larry is a very seasoned winter hiker and climber with international experience. The gist of Larry's talk was that mountains make their own weather and he cited Mt. Washington (6,288 ft) in New Hampshire as a good example of this.
Prevailing winds in the White Mountains are from the west. When they hit Mt. Washington (which has the highest ever wind speed ever recorded – 231 mph), they blow the snow on it's western side up and over the summit to it's eastern, lee side or into surrounding valleys. These areas are particularly prone to avalanches and include Tuckerman's Ravine, Huntington Ravine, and the Alpine Garden below the summit, which are all on the east side of Mt Washington. So knowing about local weather patterns, such as normal wind direction, is very important when you are hiking in wintertime and can be a good predictor of avalanche danger.
Larry also covered a few other weather related hazards that are also important in winter, the first being barometric pressure. Falling barometric pressure is indicative of bad weather, while steady or increasing high barometric pressure signifies good weather. Because barometric pressure falls with an increase in altitude, you can track barometric pressure with a wrist altimeter, provided you take your readings at the same physical altitude. If your altitude reading is falling, then the barometric pressure is rising.
Barometric pressure gradients are closely associated with cold and warm weather fronts, both of which can bring rain or snow. When a warm front moves in, warm air slides over cold air, causing drizzle, followed by heavier precipitation. Similarly, with the arrival of a cold front, cold air slides under warm air, also bringing precipitation. However, cold fronts move much faster than warm fronts (up to 35 mph) and can cause dramatic storms, including thunder and lightning, under towering clouds.
The key to noticing weather fronts and forecasting their impact depends on active observation throughout the day. Keeping an eye on cloud formations is an excellent way to remain vigilant and one that has served me well over the past few years.