Avalanche Advisory for Tuesday, December 26, 2017

Huntington and Tuckerman Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. Lower Snowfields, and Little Headwall in Tuckerman are the exception with Moderate avalanche danger due to a less developed snowpack. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions on specific terrain features.

 AVALANCHE PROBLEM: Yesterday’s snow and wind has built wind slabs over much of our terrain that will vary in hardness and sensitivity. Wind transport is still occurring and will continue for any snow that falls today. Accordingly, our surface wind slabs will continue to change in distribution, size, and character through the day. If you brave cold and wind today you will likely find at least some areas of greater stability, but the dynamic nature of our current surface snow will combine with compromised visibility to make safe travel in avalanche terrain challenging.

 WEATHER: Our Christmas day storm brought 9” of new snow to the summit. W wind in the 60-90 mph range has dominated since yesterday afternoon and will continue today. Show showers today bringing up to 4 more inches of snow which will alternate with occasional partial clearing. Current temperatures in the negative single digits F should steadily creep down through tomorrow morning. The summit will approach -30F. Windchill values could bottom out near -80F. Remember, small problems quickly turn into big problems in this weather. As always, consider the realistic consequences of something going wrong.

SNOWPACK: Poor visibility limits our ability to make observations this morning, though we expect our snow surface is comprised of a variety of firm to very firm wind slabs, with pockets softer snow and exposed crust. The extended summit wind over 80 mph yesterday and forecast to remain high today will have easily transported and compacted much of the low density new snow. The potential for additional snow up to 4” today should be similarly transported. The high density wind slabs we see following these wind events is often supportable and heavily textured on the surface. Such slabs should be stubborn to a human trigger, but the pockets of softer and smoother snow that we skiers and riders seek will be more sensitive in all but select locations. Further, we still expect avalanches to break up the crust formed a few days ago and entrain softer snow beneath it. Below this crust and softer snow, widespread hard slabs that would likely take a massive load to trigger limit our concerns for deep instability. We likely had a widespread avalanche cycle in the last 24 hours, evidence of which we may or may not see today with limited visibility and active reloading of these same avalanche paths.

The Lion Head Winter Route is open and the preferred route to the summit from the east side.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin 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 the Harvard Cabin.
• Posted 8:00 a.m., Tuesday, December 26, 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

2017-12-26