If you’re going to do any hiking in the White Mountains in winter, you need to learn about the weather patterns in the region and what forecasting tools are available for planning hikes. While many of these same techniques are useful for planning three season hikes in the area, winter conditions in the New Hampshire backcountry are so extreme that you can’t simply plan a hike months or weeks in advance and expect the weather to cooperate. I have cancelled many hikes due to sketchy weather conditions and would advocate you take a similarly conservative approach. The mountains will be there another day.
Weather Related Hazards
The main weather related hazards in the White Mountains are the wind, cold temperatures, and snow conditions.
- High wind can make walking difficult. It can accelerate heat loss from exposed areas of skin, resulting in frostbite and or create missiles, such as flying branches, chunks of ice, or tree blowdowns that can injure you.
- Cold temperatures cause ice which can make walking difficult or dangerous depending on your location. They can also accelerate hypothermia and frostbite when coupled with wind.
- Deep snow can be difficult to walk through, resulting in higher energy expenditure if you need to break out a trail with snowshoes or end up postholing because you do not have proper flotation. Blowing snow can obscure your vision, particularly above treeline, in the form of whiteouts and cause navigational problems. In certain areas, snow accumulation can also produce avalanche conditions. Avalanches occur throughout the White Mountains and not just in areas with avalanche forecasts such as Tuckerman and Huntington Ravine.
Key Mountain Weather Concepts
The wind in the White Mountains mainly blows from the west. If the wind is blowing from the south or east, it means that moist air is blowing in from the ocean which can result in rain or snow. If the wind is blowing in from the north or northeast, it is a strong indication of bad weather and heavy snow in the form of a Nor’Easter. Nor’Easters are low pressure storms centered off the coast and the Gulf of Maine that dump large quantities of rain or snow on the White Mountains and throughout New England.
Mountains Create Their Own Weather
When the wind hits the mountains, it speeds up as it flows over mountain tops. This creates numerous microclimates in the White Mountains, depending on the geography of the terrain, which can have very different weather conditions despite being relatively close together. For example, Tuckerman Ravine often experiences much heavier snowfall than the rest of the White Mountains because it is the lee of Mt Washington, the highest mountain in the region. When the wind hits Mt Washington and its subsidiary ridges, its speed increases, the air cools, and drops large amounts of snow into the Tuckerman Ravine Bowl.
High Elevations are Colder
For every thousand feet of elevation you climb, the temperature drops 3 to 5 degrees. Called the atmospheric lapse effect, this not only has temperature consequences, but can also explain why the weather on top of mountains differs from valleys and lower elevations. It also explains why the risk of frostbite and exposure increases at higher elevations when coupled with increasing wind speeds.
Fronts Bring Bad Weather
Fronts – both cold fronts and warm fronts – define the dividing line between two air masses, one of which pushes the other out so its way. When fronts collide there is a change in the weather pattern, usually with bad weather, high winds, and a change in weather direction. Here’s what the interaction between these two types of fronts looks like on the ground.
Warm fronts, associated with areas of high pressure, affect local conditions gradually and often provide observable clues, such as wispy clouds, 24 hours before their arrival. Cold fronts associated with areas of low pressure move in much more rapidly, as fast as 35 mph, and causes rapid dramatic storms, followed by cooler and clearer weather. Knowing which is headed your way and when they will arrive can help you decide where you want to be when they make their influence on the weather felt.
Winter Weather in the Whites
So how bad is winter weather in the White Mountains? Here are a few local weather facts to put things in perspective:
- Winter conditions start in November and last into May in the White Mountains – nearly 6 months of the year.
- Three storm systems, including the jet stream, converge over the White Mountains, making accurate weather forecasting a challenge.
- Pinkham Notch averages 168 inches of snowfall annually.
- The Mount Washington summit (6288′) is covered by cloud 60% of the time.
- The world’s highest recorded surface wind speed observed by man was clocked on the summit of Mount Washington on April 12, 1934 at 231 miles per hour.
- The average daily temperature on Mount Washington in January hovers around 5 degrees Fahrenheit, with winds blowing at an average speed of more than 45 miles per hour. Fog and blowing snow can reduce visibility to 200 feet or less. The windchill equivalent frequently dips to -50 degrees Fahrenheit.
- The winds on Mt Washington exceed hurricane force an average of 110 days per year. From November to April, hurricane force winds are likely to occur during two-thirds of the days.
- Snow has been recorded at the summit of Mt Washington in every month of the year, with snowfall averaging 311 inches (7.9 m) per year. Temperatures above 72 °F (22 °C) at the summit have never been recorded.
- During early January, the sun sets shortly after 4:00 pm, after only 9 hours of daylight.
Next Articles in this Series
Subsequent articles in this series will focus on:
- White Mountain Weather Information Sources and Interpretation
- Situational Awareness