This advisory expires at Midnight, 3-08-2012
Tuckerman Ravine has Considerable, Moderate and Low avalanche danger. The Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Left Gully, Hillman’s Highway and the Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Lobsterclaw, Right Gully and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely.
Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, Odell, South, and the Escape Hatch 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 except in isolated terrain features.
One thing this heat wave has going for it is we haven’t had the usual rain associated with it, which always adds to the overall enjoyment of a good thaw. This will change a bit later today due to the 50% chance of rain for the afternoon, but it shouldn’t be enough to dramatically affect avalanche danger. Although the rain should be a part of your overall stability equation, the intense warming and sluffing over the past 30 hours has helped cook out slab propagation potential near the surface. (Read on for deep instability concerns). Therefore, the current snowpack should handle the light rain amounts expected, forecasted to be somewhere around a tenth of an inch. These light amounts shouldn’t have substantial percolation rates down into the snowpack before precipitation turns to snow and we see the mercury drop like a rock with the approaching cold front. As the temperature falls below freezing in avalanche terrain liquid water that exists within the snowpack will begin freezing from the surface down stabilizing all forecast areas.
Before the overnight temperatures begin locking up the existing snowpack we do have a lingering concern about warming getting deeper in the snowpack affecting one of multiple weak layers, that have been moot until now. We have ice crusts and lens at varying depths that change from locale to locale; and buried ice bulge to ice bulge. I get lightheaded thinking about the intense slope scale spatial variability in regards to crust depths we have scattered around the Ravines that may be impacted today by the continued warming trend. Hermit Lake is currently at 45F degrees and sunny. I would expect most of our avalanche terrain to be about the same, looking at the Mount Washington Observatory’s Auto Road Vertical Profile. Some significant surface point release sluffing occurred late yesterday in Hillman’s Highway and the Duchess, and to a lesser degree in the Tuckerman Bowl, due to the daytime heating. As we progress further into our thaw I can’t ignore the nagging feeling and remote concern of a deep slab release. I do feel this potential is slim but it must be recognized as we go through our first substantial warm up in a long time. The areas posted at Considerable hold my highest attention with naturals being possible. Locations posted at Moderate take a backseat with naturals being “unlikely” but not entirely out of the question. The Lobsterclaw and Right Gully were skied heavily yesterday with deep ski penetration and compaction. Their gully nature, ski traffic, and limited size has me much less worried about deep instabilities allowing the Low rating today. I would expect more slow moving sluffs today which could entrain you, causing real problems depending on your run out. As yesterday, very high winds will continue to dampen the effects of the warm air temperatures on the snowpack. Currently winds are blowing at about 70mph, but are anticipated to be over 100mph today and even higher overnight with the intruding cold front. Their cooling affect has definitely helped limit widespread heat penetration, softening the avalanche danger potential.
Off trail will be brutal without floatation so ski’s or snowshoes are a must. Some undermining on the brushy ski out of Tuckerman should be expected. Open water holes are still present in the brook when leaving the floor of the Ravine, use caution when traveling through this area. Tonight slopes will stabilize, but our new concern may turn to fresh snow issues in the morning. Additionally the avalanche aficionado may want to watch for the development of near surface faceting as we expect ambient air temperatures around -15C with a surface snowpack at 0C. So, we are hitting the reset button and in the end if we make it through today with out much avalanche action we will be in a better place by the weekend.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856