Avalanche Advisory for Monday, March 17, 2014

Expires at 12:00 midnight

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger today. The Sluice, Lip, Center Bowl, and Chute have Considerable danger. Natural avalanches are possible and human triggered avalanches are likely in these locations. Dangerous avalanche conditions exist; careful snowpack evaluation, cautious route finding, and conservative decision making are essential. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and the Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions on specific terrain features exist. Evaluate snow and terrain carefully to identify features of concern. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions on specific terrain features exist. Evaluate snow and terrain carefully to identify features of concern. North, Damnation, and Yale have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Wind slabs are the primary avalanche problem. Loading that occurred since the widespread avalanche cycle following Thursday’s storm has continued to produce wind slab instabilities in both Ravines.  In the past 36 hours an additional 4-5″ (10-12cm) of snow fell with cold temperatures slowing stabilization. This cold air created the potential for Persistent Slabs to become our second avalanche problem due to weak snow deeper in the snowpack. The potential for larger avalanches has increased as our terrain has filled in and slabs have become more continuous.

WEATHER:  Good visibility under thin, high clouds and cold temperatures dominate the forecast today. Northwest winds in the 45-55mph (70-85kph) range with higher gusts will limit suntanning options. High temperatures will be around zero F (-18C). Winds should diminish some as well through the day.

SNOWPACK:  As mentioned earlier, wind slab developed over the weekend in much of our forecast area. Lee areas like Lip through Chute and crossloaded areas in Pinnacle through Escape Hatch  have the most widespread areas of this newer windslab which is likely to be the most reactive to triggering by a person. Areas rated Considerable are rated so due to the potential size and higher likelihood of human triggering, not due to an elevated probability of a natural avalanches. Essentially our ratings are hovering on the Moderate/Considerable line due to several factors. Before the snow fell Saturday night and early Sunday morning a surprising amount of wind blown snow was transported by westerly and southwesterly winds, refilling slopes and covering the many crown lines from the widespread avalanche activity on Thursday. Field work Friday in the Sluice and Left Gully area showed the slabs that developed during and after the storm were reactive (STE, CT12-14, 70-80 cm down) and would propagate a crack (ECTP 11,12). Though the spatial variability is obviously a problem here in our forecast area, those kind of results can be expected in a lot of areas. If you are out and about today, be wary of firmer slabs that feel strong underfoot. The finger to pencil hard wind slabs are strong but brittle so finding the trigger point could result in a larger avalanche than expected as a crack can propagate through a much thicker slab than the point at which it breaks. In other words, the surface wind slab and scattered softer slabs are just the tip of the proverbial iceberg. With good visibility and longer daylight hours, you will have the opportunity for careful assessments, terrain choices and safe travel techniques.

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 Visitor Center, or the caretakers at Hermit Lake Shelters and Harvard Cabin.
  • Posted 8:35a.m. 03-17-2014. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-03-17 Print friendly