Posted 8:10 a.m., Tuesday, April 5, 2011
Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger today. Natural avalanches are possible and human triggered avalanches are likely. The only exception to this rating is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely. Undermined snow may become and issue in this area today.
A warm wind is rattling the cabin and brief bursts of rain are splattering on the window as I type. This weather is the reason both Ravines have Considerable avalanche danger today. It is currently 48 F (9C) at Hermit Lake and our upper snow pack is soggy. Settlement patterns are visible in the Ravines and there is some evidence of recent wet loose avalanches that occurred within the new snow that fell yesterday. These small avalanches were likely triggered by the transition to rain. Over the past 24 hours Hermit Lake received 0.56″ (14.2mm) of water and the Summit recorded 1.22″ (31 mm) of water equivalent. This came in the form of snow, sleet, freezing rain and rain. Rain showers are expected to continue for the first part of the day before a cold front allows precipitation to transition back to snow. Total water equivalents today are forecasted to be between 0.42 and 0.59″ (11 and 15 mm) with a trace to 2″ (5cm) of snow accumulation later in the day. The warm weather and rain are keeping the threat of naturally triggered avalanches real. Rain and melt water are percolating into the layered snow pack and weakening the strength of existing slabs. As this continues, slab avalanches could occur and they could be pretty big. I was surprised to see that the warmth hasn’t penetrated very far into the snowpack at our snow plots as of this morning. Our temperature readings were still below 0C at 10 and 20 cm into the snowpack. (When enough free water makes it into the snow, you will get a reading of 0C in the snow.) This makes me think that existing slabs in the Ravines still have plenty of cold snow to be irritated by the percolation that is occurring and will continue to occur with more rain on the way. The type of avalanches we are concerned about today are difficult to predict. At the end of the day, the Ravines may look the same or we may have large chunky debris piles and fresh fracture lines. Due to the potential size and force of these avalanches, I would say it is wise to let this event pass before venturing into avalanche terrain.
A cold front will roll though today and temperatures up high will tumble into the teens F (around -9C) with NW winds increasing to 65 to 85 mph (105 to 137 kph) with higher gusts on the summit. The return of cold air will start a trend toward stability in the existing snowpack and an icy surface will form. We are expecting a trace to 2″ (5 cm) of new snow later today and another trace to 2″ (5 cm) falling overnight and into tomorrow. While we can expect the current snowpack to become stable by tomorrow, we may have new dry snow avalanche concerns to focus on depending on how much new snow we actually receive. If your planning on being on the mountain tomorrow you can expect icy conditions to dominate making crampons and an ice ax important tools to have in steep terrain.
The Harvard Cabin is now closed for the season. Camping in the Cutler River Drainage is only allowed at Hermit Lake Shelters.
- 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
Brian Johnston, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856