Avalanche Advisory for Saturday, February 17, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central and Pinnacle Gullies have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully to identify features of concern. All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully to identify features of concern.  All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: New snow in the past 24 hours, combined with strong winds, created wind slabs on our icy snowpack. These wind slabs are on the smaller side but are likely poorly bonded to snow beneath making human-triggered avalanches possible in wind loaded areas. Areas of wind slab will be easy to identify as they will stand out in contrast to the gray, old refrozen snow that still exists. Smooth pillows of new snow should be evaluated carefully for signs of instability or avoided all together. The new snow helped refill some of the forecast areas but “dust on crust” conditions will be likely in all but a few sheltered areas like Sluice and Lip in Tuckerman Ravine and Central and Pinnacle Gullies in Huntington. Be on the lookout for propagating cracks or hollow sounding pockets of wind slab in low rated areas as well where the icy crust can provide safer travel but a challenging self-arrest surface if you fall.   

WEATHER: The summit recorded snow with 0.5” of SWE since about 3pm yesterday afternoon. It became pretty clear while riding up the Tucks trail this morning that this snowfall was elevation dependent due to the meager inch or so on the ground at Pinkham Notch that grew in depth a bit at mid-elevations. The Hermit Lake snowplot recorded 4 cm of 11.8% new snow on the board. Winds during the snowfall from the WNW ramped up to the 60-70 mph range and moved snow into increasingly dense wind slabs. The snowfall trailed off as winds diminished. Temperatures dropped yesterday from a high of 30F on the summit to -9F early this morning. Winds are currently light under bluebird skies. Winds will diminish further this afternoon to the 20-35 mph range as temperatures rise to 11F under increasingly cloudy skies.

SNOWPACK: Deeper instabilities in our snowpack were more or less erased with the two warm spells that occurred this past week. Cold temperatures returned overnight and have once again locked up percolating water and sintered old snow. In our forecast areas, you will find the refrozen snow will easily support your weight except in areas around bushes or boulders. If you look hard enough, you may be able to find some early faceting going on around the crust but it is unlikely to be a weaker layer than the new and old snow interface or the soft early storm snow.  

If you are in town for the weekend and looking for something to do, join us at International Mountain Equipment at 5 pm for Ryan’s talk on snow stability tests and how to use them. With luck, we will live stream this on Facebook Live.

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 8:01 a.m., Saturday, February 17, 2018. A new advisory will be issued tomorrow.

Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-2-17