Avalanche Advisory for Friday, March 16, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features; identify features of concern. North, Damnation, and Yale have Low avalanche danger. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has CONSIDRABLE, MODERATE, and LOW avalanche danger. Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Dangerous avalanche conditions exist. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and the Lower Snowfields have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. The Little Headwall has Low avalanche danger.

AVALANCHE PROBLEM: Strong NW wind created thick wind slabs yesterday. These will be found in greatest concentration in Considerable rated areas. While human-triggered avalanches are more likely than natural avalanches, wind slabs have the potential to run far today. A mix of cross-loading and scouring has taken place on other slopes. Pay close attention to this interplay as it may be easiest to trigger this wind slab on its outer edges. The boundary of wind slab and old surface may be blurry due to newer snow over the old ice crust. Slopes with a Moderate rating today, particularly Central Gully in Huntington, should not be taken lightly. Areas of more reactive snow will likely be found in the most sheltered areas and should be negotiated appropriately. Old icy surface or older firm wind slabs may be found in areas and will make great climbing, but also provide the potential for sliding falls. An ice axe and crampons will be useful in steep terrain today.

WEATHER: The snowy mid-March we are experiencing continued yesterday as the Summit recorded 7.3” of snow yesterday with a water equivalent of 0.75”. The arrival of this snowfall was split, early in the morning and then another dose after dark with snow flurries and blowing snow all day. Wind stayed W and WNW for the day with speeds in the 60-80mph range with a peak gust of 98mph. Unsettled weather will linger over the region today, keeping the summits in the fog with intermittent upslope snow showers bringing up to 2” of snow. Winds will remain NW 50-70mph to start the day and increasing in the afternoon with gusts topping 100mph after dark as a cold front moves over NH. The current temperature on the Summit is 1F and should drop through the day to the negative-teens F tonight.

SNOWPACK: The Mount Washington Observatory recorded 27” of snow (2.57” SWE) over the past 72 hours that was finally subjected to classic strong NW wind. A combination of scouring and loading has taken place. The heaviest loading is on slopes in the direct lee of NW wind, particularly at mid-elevations and under terrain features. This magnitude of wind (sustained 60-80mph) will have created firm, stubborn wind slab as well as a combination of scouring and cross-loading on slopes with a southern or northern exposure. This wind slab in places now sits on previous layers of wind slab that formed over the past two weeks. It is likely that the tensile strength of yesterday’s slab will bridge over weak layers that may linger on deeper interfaces, but an avalanche stepping down into these other weak layers is possible.

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 8:25 a.m., Friday, March 16, 2018. A new advisory will be issued tomorrow.

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