Avalanche Advisory for Thursday, 4-12-2012

This advisory expires at midnight, Thursday 4-12-2012

Tuckerman Ravine has MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.  Heightened avalanche conditions exist on specific terrain features.  Evaluate snow and terrain carefully to identify features of concern.  The Lobster Claw and the Little Headwall are not posted due to lack of snow.  Huntington Ravine is under a General Advisory. You will need to do your own snow stability assessments when using avalanche terrain in Huntington. A danger of falling ice exists, and will persist until it all comes down.

Some brief clearing yesterday morning with some flat light views into avalanche terrain was bullied out by a dropping cloud ceiling and the return of snow showers.   The summit recorded another 2” (5cm) of snow giving the higher elevations 2 feet of accumulation since the weekend.  The past several inches have fallen with low wind speeds, which are forecasted to pick up today.  Velocities should increase up to 40mph from the current of 17mph and shift from the N to the NW.  This may begin transporting some new snow sitting above treeline from the past 36 hours down into avalanche terrain particularly the up reaches of the Sluice and the Lip.  Cross loading of east facing aspects is also possible but to a lesser degree.  Light snow showers this morning will continue until some clearing begins this afternoon giving us perhaps an additional inch to weigh in the equation. Rain is also not out of the question.

Depending on exactly how today’s weather plays out we are teeter tottering between Moderate and Considerable avalanche danger particularly SE and E facing slopes, namely the Sluice, Lip, and Center Bowl.   First, the reasons why I believe we won’t quite make it to a Considerable rating today, but will be on the upper end of Moderate for the aforementioned locations.  The vast majority of snow this week available for transport from the higher elevations down into the avalanche terrain has already happened.  High winds gusting to 80mph occurred on Monday tapering to gusts into the mid 50’s through Tuesday morning.  An occasional spike later that evening into the upper 40’s has since mellowed to 30mph or lower.  Generally, the only snow left available for today’s maximum winds is about 2-3” which has bonded and settled over the past 36 hours due to rising temperatures.  Bigelow Lawn and the Alpine Garden, two areas that typically load snow into Tuckerman, were very close to the freezing mark and sensors show they briefly exceeded the critical 32 degree point.  Below this elevation exists all of our avalanche terrain which in turn also went above freezing with some paths like lower Hillman’s hitting about 36F.  Dropping temperatures overnight has refrozen free-water strengthening the upper snowpack, especially slopes at lower elevations.  This has helped the stabilizing trend, but has had limited effect in some of our deeper slabs in the upper reaches of Tuckerman’s avalanche terrain. However, existing slabs no longer deserve a definition that reads that natural avalanches are possible and human triggered avalanches are likely.  Saying this, it’s important to recognize that as we drop to “Moderate” our current widespread deep slabs should be respected and although the likelihood of initiating a failure causing an avalanche is lower than yesterday, it would still be close in size-Large. The possibility of a human triggered avalanche is greater high in the Ravine’s colder snow.  Slopes near the Headwall elevation from the Lip over to the Chute have the highest potential for weak slabs. 

There are several issues to watch that would push us over the fence from the upper end of “Moderate” to “Considerable” todayIf snow accumulations exceed an inch today, winds shift to the NW earlier than expected, and maximum winds exceed 40mph think about an increasing avalanche danger.  The most threatening factor to watch that can increase the avalanche danger most rapidly today is the potential for rain.  Although the higher elevations are expecting some snow our avalanche terrain to the 5000ft level could see some liquid today.  Water equivalents for Gorham and North Conway are showing up to 0.15” on the upper end.  Some of that moisture is currently being squeezed out as snow above 2000ft.  If rain does occur it should be light, but through some orographic effect and clouds interacting with the terrain the final amounts between snow and rain could exceed the valley expectations. I would be thinking more about the potential for small natural avalanches possibly stepping down into something larger if additional snow loading and particularly rain occur today.  Watch for rain and loading evidence as your day unfolds and change plans accordingly to lower your risk.     

As if avalanche danger wasn’t enough to make you stay out of the area, you need to know that the Center Bowl and Lip area have numerous deep crevasses. Expect all of these to be covered visibly by new snow, which makes for weak bridges that can collapse under your weight. You will not be able to assess this hazard safely because of their hidden nature and the consequences of falling into one of these crevasses are severe.  We recommend avoiding this area entirely. Hikers should not use Tuckerman Ravine to access the alpine zone and the summit of Mt. Washington. Also, you should not descend down from these areas into the Ravine.     

Please remember:

  • 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.  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

2012-04-12 Print Version