Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions exist which require careful snowpack evaluation. Cautious route finding and conservative decision-making is essential.
The forecasted 1-3” of new snow today is already getting close to being exceeded as of 7am. Between 2 and 3” of snow has fallen since midnight associated with a building west wind. Speeds began in the 40mph (64kph) area and have slowing been creeping up this morning. This trend should continue to the forecasted velocities of 70-90mph (112-144kph) before briefly subsiding late in the day. Snow is expected at higher elevations today and tonight with an additional 1-3” after dark bringing totals up to 6” by morning. All this data makes us believe we will have growing instabilities through the day and into tomorrow. Once again, we should see denser slabs deposited on top of the lighter unconsolidated snow that fell early this morning creating a new weak snowpack. New snow at our Harvard Cabin manual snowplot gave us an average snow density of 8%. In many strong lee terrain features of moderate W winds this thin loose 8% blanket of new snow should act as the dominate weak layer for today’s new slabs to fail on. Winds are currently gusting to 70-72mph (112-115kph) already, so instabilities have already been growing in the largest E facing snowfields like the Tuckerman Headwall and Odell and Central gullies in Huntington. As the day continues, E faces will lead the charge as the main concern for natural avalanche activity. We will also see cross loading occur on S and N facing slopes. Expect areas like Right gully which faces south and South gully in Huntington which faces north to linger behind the dominate instabilities of E facing aspects. Some outliers that are still a bit scrappy and peppered with brush, rock, turf and smaller snowfields will struggle to meet the Considerable ratings today. Specifically, Hillman’s Highway and the Lobster claw in Tuckerman and North gully in Huntington will be substantially behind E aspect instabilities, but will have growing unstable slabs through the forecast period.
Some key points to remember in the field today: 1. **Growing instabilities exist today due to new snow and a building high velocity wind reaching 100mph tonight. These new issues are in addition to the left over unstable slabs from the 6” that fell on Wednesday and Thursday. Although all areas have the possibility for natural avalanches with the avalanche forecast period, E faces will lead as the main concern while some others will become weak enough for natural failure quite late. 2. **Poor visibility and blowing snow will make quality route finding difficult to avoid instabilities whether you are ascending or descending. It is also a busy Holiday weekend which means numerous human triggers may exist above you even though no telltale tracks can be seen. 3. **High winds and blowing snow above treeline may make navigation difficult. Be open to changing your plans when new data makes it a wise a prudent decision.
Safe travel in avalanche terrain requires training and experience. This advisory is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin. Posted at 8:29am.This advisory expires at midnight. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger USDA Forest Service White Mountain National Forest (603) 466-2713 TTY (603) 466-2856