Avalanche Advisory for Sunday, February 25, 2018

Huntington Ravine may reach CONSIDERABLE and MODERATE avalanche danger. Yale, Central, Pinnacle, Odell, South, and Escape Hatch gullies may reach Considerable avalanche danger. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. North and Damnation Gullies may reach Moderate avalanche danger.  Evaluate snow and terrain carefully to identify features of concern.

Tuckerman Ravines may reach CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s Highway may reach Considerable avalanche danger. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. Lobster Claw, Right Gully, and the Lower Snowfields may reach Moderate avalanche danger.  Evaluate snow and terrain carefully to identify features of concern. The Little Headwall is an open stream and is not a viable route out of Tuckerman Ravine.

AVALANCHE PROBLEM: All forecast areas this morning are icy and firm with low avalanche hazard. Incoming precipitation will create a widespread wind slab avalanche problem throughout our forecast terrain and increase our avalanche danger to Considerable as the day progresses. The size and tendency of avalanches to release naturally will largely depend on the amount of snow that falls this afternoon. The forecast snowfall of four to six inches of snow in the higher terrain is plenty of snow to create slabs that are capable of knocking you off your feet and carrying you down slope. Combined with an icy bed surface on our steep 35-50-degree terrain, even a small avalanche today can have serious consequences. While winds from the south might seem to target only north facing terrain for wind loading, count on cross-loading and sluffing to load east facing slopes in a similar fashion. If the steep icy base and wind loading aren’t enough of a challenge today, remember that this precipitation will be warming and becoming increasingly dense. This will create an “upside down” snowpack that may begin to act like a wet slab, making the new snow more sensitive to a human-trigger.

WEATHER: Yesterday, no precipitation fell after sunrise as the higher terrain remained mostly in the clouds while temperatures remained below freezing at Hermit Lake. The weather system currently approaching is forecast to bring 4-6” of new snow on wind that should shift from SSE to SW and finally W after dark. Summit wind speed will increase as it wraps around, pushing towards 50 mph this afternoon and likely exceeding that tonight. Temperatures are forecast to trend upwards through this storm with a high near 30F on the summit forecast for this afternoon. As snowfall tapers off late today we may see a changeover to sleet and other mixed precipitation types. Precipitation should end tonight as wind continues to increase and ultimately shifts NW tomorrow.

SNOWPACK: Today’s new snow will fall on an icy refrozen surface. Friday night, precipitation fell in mixed forms and was dominated by ice pellets which contributed to the generally smooth and hard snow surface in our terrain. Beyond providing a slick bed surface for slabs forming today, the existing snowpack does not pose stability concerns. As the day and the storm progresses we will see new slabs develop from the new snow and wind. Varying forecast snowfall totals mean that you should pay close attention to the weather and developing conditions on the ground when making terrain choices. Shifting winds will have the potential to rapidly build touchy slabs on a variety of aspects.

A number of other spring-like hazards exist in our terrain and will become masked by snow through the day. This includes waterfall holes, moats, undermined snow, and rocks that are both in and below our avalanche paths. The John Sherburne Ski Trail holds icy snow with patches of water ice and bare ground.

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 7:45 a.m., Sunday, February 25, 2018. A new advisory will be issued tomorrow.

Frank Carus/Ryan Matz, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-2-25