Avalanche Advisory for Monday, December 25, 2017

Huntington Ravine has HIGH and CONSIDERABLE avalanche danger. Central, Pinnacle, Odell, and South Gullies will reach High avalanche danger. Natural avalanches likely and human triggered avalanches very likely. Travel in avalanche terrain is not recommended. All other areas in Huntington will reach Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely.

 Tuckerman Ravine has HIGH avalanche danger. Natural avalanches likely and human triggered avalanches very likely. Travel in avalanche terrain is not recommended. Lower Snowfields and Little Headwall in Tuckerman are the exception with Moderate avalanche danger due to a less developed snowpack. Heightened avalanche conditions on specific terrain features.

 AVALANCHE PROBLEM: Today’s significant storm snow and wind will build reactive wind slab over terrain lee to W and NW wind and crossload other aspects by this evening. Lighter winds this morning coupled with heavy snowfall could allow a less cohesive storm slab to briefly develop. Before this becomes much of a concern, wind speeds will rise and build the more cohesive and reactive slabs that are our primary avalanche problem. Instability will likely peak this evening before sustained extreme wind overnight scours many areas and builds firmer and more stubborn slabs. There is a strong chance that avalanches today will break up Saturday’s crust and entrain soft snow below, resulting in a larger slide than surface slabs might suggest. Areas not receiving a High danger rating today lack the snowpack development to produce a large avalanche, though the likely but smaller human triggered avalanches in these areas could still have dire consequences.

 WEATHER: We’re all getting a heap of snow for Christmas! It’s coming down already and by tomorrow we will likely have over a foot of new snow on the mountain, with heaviest snowfall earlier in the day today. Southerly wind in the mid-30’s mph range during the heaviest precipitation will increase and shift through W to NW as snowfall tapers but continues through today and tonight. Sustained wind speeds over 70 mph with gusts nearing 100 mph can be expected. Summit temperatures will trend downwards from single digits above to single digits below zero. Light snow will continue tomorrow as W to NW wind continues to push the century mark. This weather follows a major crust building event on Friday and a subsequently unremarkable Christmas Eve. Limited snow was available for wind transport yesterday, but plenty will be today.

SNOWPACK: Today’s storm will be deposited on a layer of 1-2 cm breakable crust that formed Friday evening and exists on most of our terrain. The snow that fell earlier on Friday remains soft and dry beneath this crust. We expect avalanches today to occur above the crust, but realize that any sizable avalanche will break up this crust and entrain Friday’s storm snow below it. The avalanches that are likely to occur today will likely be large relative to current path development. It’s a great day to recreate in the snow without exposing yourself to avalanche terrain. The John Sherburne Ski Trail now has good coverage and should ski well as the new snow accumulates!

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., Monday, December 25, 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