Avalanche Advisory for Tuesday, April 10, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger. 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. Lobster Claw, Right Gully, Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. Left Gully, Hillman’s Highway, the Lower Snowfields, and the Little Headwall have Low avalanche danger. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Wind slab formed since late Sunday is our primary avalanche problem. Generally on the thin side and thus not likely to produce large avalanches, this layer remains possible to human trigger. It will likely vary from stubborn to touchy across the terrain. A secondary avalanche problem is the older and now generally stubborn wind slabs which formed on Friday and Saturday nights, the culprit of our widespread cycle of somewhat small human triggered avalanches over the weekend. This layer is beneath the more recent slabs in some areas and at or near the snow surface in others. Low rated areas have significant old refrozen crust at the surface, presenting a long sliding fall hazard while still holding small pockets of wind slab. It’s certainly a “Low” doesn’t mean “No” avalanche danger kind of day. Moderate rated terrain holds more widespread wind slabs, though it will be difficult for travelers to visually discern thin from thicker slabs as well as the older and more stubborn slabs from the newer and touchier slabs.

 WEATHER: Wind decreased last night as temperatures rose to near 10F on the summit. It looks to be a pleasant, wintry morning, with W wind hovering around 20 mph and temperatures rising to the teens on the summit. Increasing clouds and a weak weather disturbance later today could bring a trace to 2” of additional snow, with scattered snow showers possibly giving us similarly small amounts through the end of the day tomorrow. Wind is forecast to remain under 30 mph on the summit for the next 36 hours, limiting concerns for new wind slab development from these small amounts of new snow.

SNOWPACK: Winter is back, with layers of wind slab formed since Friday night in much of our terrain. The thick and robust refrozen crust which is under this recent snow and still present at the surface in some areas limits stability concerns to slabs at or near the surface. Friday night, Saturday night, and Sunday night all had distinct wind events which coupled with the recent snowfall to ultimately result in the current 2-3 layers of wind slab in the terrain. These slabs are all relatively soft though vary slightly (4F-F), and the most recently formed layers should be most reactive. Where old refrozen crust is not present at the surface, the snowpack looks fairly uniform, but really is quite spatially variable. We suspect that visually similar snow will vary from dust on crust to possibly 20” total of layered wind slabs. Additionally, bonding to the old crust seems to vary across the terrain. This means that there will be a distinct element of uncertainty in your snowpack observations. Ask yourself, “What will happen if it avalanches?” as you carefully choose terrain, and you’ll likely find some good wintry turns on this April day.

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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.
• Posted  8:10 a.m., Tuesday, April 10, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2858