Posted 8:00a.m., Friday, March 18, 2011
Tuckerman and Huntington Ravines have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The only exception to this rating is the Little Headwall in Tuckerman which has Low avalanche danger. Natural and human-triggered avalanches are unlikely in this areas, however this slope presents its own hazard today. Read below for more details.
Hold onto your hats, today is going to be a bit of a wild ride. If you’ve ever been to the Caribbean during hurricane season, you’ll be able to imagine what it feels like at Hermit Lake right now: warm, humid, and windy. Temperatures are currently a balmy 43F (6C) and every so often a strong gust rocks our cabin. Today’s primary stability concern is directly related to this warmth and the resulting free water that is percolating downward through the snowpack. More often than not, a day like this in mid-March would have avalanche danger ratings a notch or two above the current Moderate rating. The difference is in the way a couple of factors have played out.
First are temperatures in the ravines. The 5300′ elevation just went above freezing early this morning, while the 4300′ level has been above freezing since midday yesterday. This is creating some free water percolating down into the snowpack, which has the effect of raising the instabilities. However, during the day temperatures are forecasted to drop back down below the freezing mark, which will increase stability. A second factor playing out today is precipitation. In the morning there is a chance for rain in the ravines and perhaps mixed precipitation on the summit. Only a small amount of liquid is expected, up to 0.2″ (0.5cm). If rain falls heavier than expected, or if temperatures stay warmer than expected, avalanche danger may increase. The third prominent factor related to today’s stability is the snowpack. Last Friday we had a soaking rain followed by freezing temperatures and snow, then Tuesday was a warm sunny day that was followed with a small amount of new snow changing to mixed precip on Wednesday. Areas that received loading from SW winds on Wednesday but did not avalanche will be the most suspect today (Odell, South, and Escape Hatch avalanched with this snow). Given the sum total of how these variables will interact today, I believe natural avalanche activity is unlikely but not impossible. Pay attention to what the weather and snowpack are telling you as you make your travel choices. As temps and the precipitation potential drop, the avalanche danger will subside as well. At some point late today or tonight, after everything has frozen back up, I expect avalanche hazard will take a back seat to the dreaded “long sliding fall.”
The Little Headwall is rated Low today, but I would like to remind you of the rain we had last week. This effectively undermined the snow from below the slope, and today the warmth is weakening the upper layers of snow. Unfortunately the Little Headwall has had a tough time developing this winter, so the snowpack is thinner than usual. Based on this, I’d recommend treading lightly in this area or avoiding it altogether for now.
- 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.
- This advisory expires at midnight. 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