This advisory expires at 12:00 midnight tonight.
Tuckerman Ravine and Huntington Ravine have CONSIDERABLE avalanche danger today. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential.
It’s ironic, isn’t it? On the last day of winter 2013, what will likely be the largest winter storm to hit the White Mountains yet this season has arrived. While snow accumulations are already on the rise, so is the avalanche hazard. During this storm, I expect avalanche danger to push the boundaries of the Considerable rating. The risk of naturally triggered avalanches is significant, and your ability to assess the risk from below will be very poor, so think hard about even going into the bottoms of any slide paths today, especially the floor of Tuckerman. I don’t want to play Debbie Downer and ruin the celebration of the last day of winter, so let me simply suggest that the party take place outside of avalanche terrain. Resorts, backcountry ski trails, and below treeline gladed areas around the mountains would be good options.
Yesterday’s field work provided a lot of information to give us a baseline for where we’re starting out today. All areas of Huntington, Hillman’s Highway, Left Gully, the Chute, and far left side of the Center Bowl all had very good stability, with exceptions in small pockets here or there. This was due to strong winds scouring snow away or packing it into stiff slabs that would require some force to stick a pencil into. In more protected locations, e.g. the Lip and Sluice, the wind has less effect and therefore the surface slabs developed less strength. Beneath both the softer and the harder slabs, there was a weak layer composed of snow crystals deposited Sunday as well one over the latest rain crust from last Tuesday. This is the weak layer that failed and caused a 70cm deep hard slab avalanche in the lower Chute area on Sunday night. It’s also the reason why I think any avalanches that take place today in the Bowl, Lip, or Sluice may step down into this hard layer and significantly increase the size and consequences of the slide.
So far today, we’ve got about 4″ (10cm) of new 10-11% density snow. Total forecasted accumulations are 8-12″ (20-30cm) for today and another 8-12″ tonight. Winds today will be from the SE, slowly shifting to the E and decreasing slightly. This puts a lot of our avalanche terrain on the windward side of the mountain. Therefore windloading today will be kept down somewhat, but cross loading of N-facing slopes should be expected. Examples include Dodge’s, Hillman’s, and Left in Tuckerman and Escape Hatch, South, and Odell in Huntington. I also think Pinnacle will become loaded due to the eddy effect under the rock buttress. Since they’re starting with better baseline stability, these areas will be playing catch-up to the other areas that are starting with more instability. Despite unfavorable wind directions, these areas facing into the wind will still receive additional snow load and will be increasing in avalanche hazard through the day. We are expecting a slight lull in the snowfall rate later this morning and early afternoon, but by the end of the afternoon rates should pick up again. I suspect a lot of tonight’s forecasted total will fall before this avalanche forecast expires, so I want to be clear that I’m basing today’s rating on where I see the avalanche danger for the daylight hours, sometime overnight the avalanche danger will likely exceed today’s rating.
- 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 8:30a.m. March 19, 2013. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856