Tuckerman Ravine has Moderate and Low avalanche danger today. The Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely, however, watch for unstable snow in isolated terrain features.
Huntington Ravine has Low avalanche danger today. Natural and human triggered avalanches are unlikely, however, watch for unstable snow in isolated terrain features.
Although barely worth noting due to scant amounts, yesterday marked the 15th day in row, and the 23rd day of the month, that the higher elevations have received precipitation. This streak will continue as a system approaches the region later today, expected to give the landscape a 3-5” (7.5-12.5cm) shot of snow. I’ll say more on this developing weather event in a minute.
Tuesday gave us good conditions to spend copious amounts of time in the field. Our assessments in Hillman’s Highway, Left gully, and the greater Lip area verified the morning advisory ratings. Locations posted at Moderate still harbor enough concern to keep them a step above Low, however another day of consolidation has certainly brought these slabs closer to this lower rating. The likelihood of a human trigger is still “possible”, but on the spectrum we are closer to the “unlikely” descriptor than “likely” when looking at the neighboring definitions of Low and Considerable. The variability of slab hardness and thickness are still the two main factors on your ability to trigger these slopes from the Sluice over to the Chute. It will be important to evaluate the snow stability under foot/ski as you move due to these changing slab properties. Pay particular attention to the propensity for a slab to fracture and propagate leading to failure as you enter it’s thinnest outer edges. This is a common cause of our post storm human triggered avalanches. In addition to thin slabs over a weak layer, you may also enter small lee areas in the terrain that were more protected from wind hardening than nearby slopes, which kept them a bit softer and weaker. The main point of both of these examples is to pay attention to changing stability as you move in the terrain. Also be weary of trusting and extrapolating earlier stability tests even though slope angle and aspect are similar. By evaluating snow and terrain carefully the experienced and skilled mountain climber and skier should find reasonable routes within areas posted at Moderate until snow develops new problems late in the day.
3-5” (7.5-12.5cm) of snow is anticipated to begin late in the day, fall through the night, and perhaps into daylight tomorrow morning. This entire weather event shouldn’t play too much of a factor on stability for the typical recreational period today. I am cognizant that technically this advisory is valid until midnight so realize as we enter the last hours of the day avalanche danger may have increased enough to warrant a rating increase. But obviously this is more of a concern for those benighted than those intentionally recreating. It would be wise however to watch for new precipitation issues if it begins a bit earlier than forecasted. If snow falls in the early to mid-afternoon you can anticipate some thin new slabs today in strong lee slopes protected from NW winds. Areas currently at Moderate would be the first affected, but not enough to move them to a higher rating. As snow falls overnight winds will shift through the N to the NE. You can expect some new slab avalanche concerns tomorrow on slopes with primarily a S facing component.
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 8:10 Wednesday 3-27-2013. 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