Avalanche Advisory for Monday, February 19, 2018

Huntington Ravine has CONSIDERABLE, MODERATE, and LOW avalanche danger today. Central and Pinnacle have Considerable avalanche danger. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. Yale, Odell, South, and Escape Hatch have Moderate avalanche danger. Evaluate snow and terrain carefully; identify features of concern. North and Damnation have Low avalanche danger. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has CONSIDERABLE, MODERATE, and LOW avalanche danger. Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Large avalanches in specific areas are possible. Dangerous avalanche conditions exist. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and Lower Snowfields have Moderate avalanche danger. Evaluate snow and terrain carefully; identify features of concern. The Little Headwall has Low avalanche danger.

AVALANCHE PROBLEM: Today’s avalanche problem is wind slab. Continued wind transport today will add more snow to pre-existing wind slab. Areas of greatest concern are slopes in the lee of W and NW wind (Considerable rated areas) as well as mid-elevations of other aspect, such as Hillman’s and Yale. This wind slab has connected several forecast areas in Tuckerman Ravine, meaning an avalanche triggered in the Lip may include Center Bowl and possibly more. Some areas of steep terrain do not have this wind slab and are wind-scoured to the older, icy snow surface. Crampons and an ice axe will not go amiss on any adventure in steep terrain today.

WEATHER: A total of 5” of snow fell yesterday through the day. While snow was falling, wind shifted between the W and NW and ranged from 40mph to 70mph, with strongest wind speeds recorded around noon. As snowfall died last night, wind speeds diminished and shifted to the SW. This morning, the wind is from the SW and currently blowing 42mph. Wind will likely trend toward the W and should remain in the 40-60mph range for the day. High pressure will keep skies clear for this morning before the incoming warm front approaches. It looks like temperatures should remain below freezing for daylight hours. Fog should develop in the afternoon as the temperature starts to rise with mixed precipitation possible in the evening.

SNOWPACK: Wind slab that formed over the weekend sits on a firm bed surface that has gone through multiple melt-freeze cycles. Yesterday’s 5” of snow fell on increasing wind speeds, creating large areas of wind slab. Wind speeds were at times strong enough to scour areas down to the icy bed surface, though these tend to be in lower portions of our terrain and present themselves with the appearance of gray snow or may even have a reflective sheen with today’s sun. Areas with a northerly and southerly exposure have the most scouring down low and contain firm-looking sastrugi up high, including Damnation and North in Huntington as well as the looker’s left fork of Hillman’s Highway. Places of most concern today will be the Sluice through Chute in Tuckerman and Central and Pinnacle in Huntington. Smooth wind slab dominates these areas and has covered rocks and old crown lines that were visible on Friday, giving an indication to the amount of loading that took place yesterday. Current blowing snow on SW wind of 45 mph is a sign that wind transport has not ended and our fetch still has transportable snow. SW shifting W wind today will allow areas of wind slab to grow in size today. While many gullies have old surface down low due to wind scouring, mid-elevations contain the largest smooth-looking wind slab that could prove touchy to human-triggers today.

• 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 8:30 a.m., Monday, February 19, 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