Avalanche Advisory for Monday, March 31, 2014

This advisory expires at 12:00 midnight.

Tuckerman and Huntington Ravines have Moderate avalanche hazard. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions will exist on certain terrain features. Evaluate snow and terrain carefully. Slopes with a southerly aspect may push towards Considerable this afternoon due to an increasing potential to produce natural avalanches. I would avoid larger slopes like the Sluice, Lip, Center Bowl ad Central Gully as well as those gullies with longer paths that have a stronger southerly aspect such as Lobster Claw, Right Gully, Damnation and Yale.

AVALANCHE PROBLEMS: The primary hazard today will be Wind Slab. New snow today, driven by north winds, may build Wind Slabs on slopes with a southerly aspect and crossload other areas. While not particularly large due to the scant amount of snow expected, the potential is there for a large enough avalanche to hurt you. The secondary hazard is the low probability but high risk concern of triggering a Persistent Slab. Recent rain and warm temperatures haven’t reached far enough into the snowpack to stabilize some weaker layers and has added more load to lingering Persistent Slabs. Remain vigilant in avalanche terrain and continue to apply solid avalanche safety techniques.

WEATHER: It appears as though Mt. Washington only caught a glancing blow from the storm that passed yesterday. The bulk of the precipitation we received came as snow early yesterday (2.5″ at the summit). After this, sleet fell lightly before changing over to a light drizzle of rain. Late in the day, ravine level temperatures fell below freezing and stayed there through the night. During this time summit temperatures were much warmer than at Hermit Lake and in the ravines.

Again today, much of the precipitation is falling to our south. We are expecting mixed precipitation turning to snow late this morning, with daytime totals reaching about 0.15″ of water equivalent. The Obs has forecast 1-3″ of snow from today’s precip, most  likely to come late in the day on strong N winds.

SNOWPACK: We have some unanswered questions about the snowpack which complicate the effort to forecast avalanche hazard. First and foremost, how deeply did warmth and liquid precip penetrate into the cold winter snowpack over the previous two days, and does this change at all due to aspect and angle? Also, what avalanched yesterday is a question that will remain unanswered until visibility improves. Weather data for the past 24 hours indicates that the amount of rain and associated warm temperatures were not enough to penetrate deeply into our snowpack. While the snowpack did not go isothermal, a sufficiently thick melt-freeze layer  at the surface now exists to bring down avalanche hazard.  If we receive the upper end of the forecasted snow amounts, we will have new wind slab issues, particularly on S-facing slopes and some cross-loaded E-facing slopes. Pay attention to how much snow has fallen if you’re out and about today. Continued summit fog and new snow will make assessment challenging today. New wind slabs are likely to be touchy on steep terrain and could grow quickly. Persistent Slabs are still a concern. Though the January ice crust and weak facet layer beneath have been mostly swept out of slopes in our forecast area, it is still around as are other weak interfaces between old wind slabs.

OTHER HAZARDS: Undermined and collapsing snow bridges are a potential issue. This is mostly a concern for people looking to ski the Little Headwall or brook above. Be careful around any stream bed today as the snow covering it may not hold your weight.

On today’s project list is completing the report on Saturday’s avalanche on the Southeast snowfield. Hopefully some premature information and otherwise speculative information erupting in social media circles can be corrected and some lessons learned.

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.
  • Posted 8:00 a.m. 3-31-2014. A new advisory will be issued tomorrow.

Frank Carus/Jeff Lane, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-03-31 Print friendly