AVALANCHE ADVISORY FOR THURSDAY, APRIL 6, 2017

This advisory expires at Midnight.

Tuckerman and Huntington Ravines have MODERATE avalanche danger today. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. The only exception to this rating is the Little Headwall which has Low avalanche danger, with natural and human triggered avalanches being unlikely. Open water exists in Little Headwall and will increase as the day progresses.

 AVALANCHE PROBLEM: With our moist surface snow continuing to become saturated via rainfall and warming through the day, Wet Slabs are our primary avalanche problem. The continued warm temperatures and significant amount of precipitation in the forecast will increase the likelihood of these slabs becoming sensitive to human trigger as the day progresses. The size of a resulting avalanche should also increase as moisture penetrates deeper into the snowpack. While stubborn in many areas to a direct human trigger, today’s secondary avalanche problem of Loose Wet sluffs could more easily initiate a deeper wet slab.  These sluffs are all but certain to be initiated by any skier or rider on steep terrain.

 WEATHER: While winter made another comeback earlier this week, above freezing temperatures returned to our forecast areas early yesterday morning and persisted through the present time. A high of 37F is forecast for the summit today. Moderate wind from varied directions yesterday and today lack ability to transport our wet surface snow. Critical to today’s snowpack stability will be the full inch of rain forecast to fall today, beginning around noon.

SNOWPACK: Change remains the constant characteristic of our snowpack and snow surface. The 7-10” of snow that fell Tuesday, including deeper drifts, warmed significantly starting yesterday morning and has not experienced a refreeze. A breakable melt-freeze crust under the new snow and on top of last Friday’s snow acted as a sliding surface in stability tests yesterday, and a deeper, supportable rain crust formed early last week underlies these layers. While limited in ability to propagate a crack, significant wet sluff activity or a human trigger in the right location could result in a wet slab release.  As moisture increases in the snow brought by these two recent storms, an avalanche could step down or entrain snow to the rain crust of early last week, resulting in a large release of wet, heavy snow. In addition to stability concerns, today’s warming and rainfall will increase the presence of other springtime hazards, particularly on ice routes. Running water will undermine snow and weaken snow bridges, ice and rock fall could occur, and generally soggy conditions will soak through anything but rubber rain gear. If on the mountain, remember that diminished rewards might suggest you assume a lower level of risk, and that skier-compacted areas like the Sherburne might be your most enjoyable ski option.

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 Harvard Cabin.

Posted  8:10 a.m., Thursday, April 6, 2017. A new advisory will be issued tomorrow.

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

2017-04-06