Avalanche Advisory for Friday, February 2, 2018

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central Gully has Considerable avalanche danger. Careful snowpack evaluation is essential. All other forecast areas have Moderate avalanche danger. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl, Chute, Left and Hillman’s Highway have Considerable avalanche danger. Careful snowpack evaluation and cautious route-finding are essential. Lobster Claw, Right Gully and Lower Snowfields have Moderate avalanche danger. Heightened avalanche conditions may develop on specific terrain features. Evaluate snow and terrain carefully. Little Headwall is no longer filled in with snow and is not rated. The Lip still contains a large void in the snowpack from the wet avalanche on January 12 or 13 and creates a significant terrain trap and fall hazard beneath the rollover and out of view from above.

AVALANCHE PROBLEM: Increasing wind speeds will build slabs as wind from the northwest begins to ramp up midday. 2.5-3” of light density snow in the past 24 hours, and potentially 2” more today, will be blown into the terrain by these winds. A wind slab avalanche could be thick enough to carry you and possibly bury you beneath Considerable rated slopes in Tuckerman Ravine. A combination of snow and terrain factors make the Considerable rated areas most likely to develop these thicker wind slabs in larger areas. All Moderate rated areas will flirt with the higher rating with smaller but sensitive wind slab developing but with a little less snow available in the flat, treeless fetch zone. Additionally, dry loose avalanches will become a problem in the steeper terrain in both Ravines.

WEATHER: Decreasing temperatures and increasing winds are on tap for today.  We are starting at 3F on the summit and will drop throughout the day as the cold front pulls away.  By nightfall, we’ll be well into the negative digits, possibly -20F by midnight tonight. Winds overnight were light at 30 mph from the west and are expected to ramp up, shifting to the north west at 60 to 80 mph.  Snow showers capable of producing up to 2” of new snow, combined with lingering summit fog and blowing snow will severely limit visibility.  Traveling today will be challenging especially in the afternoon. Tomorrow looks to be the opposite of today, starting cold with strong winds. However warmer air, slackening winds and possible clearing in the afternoon could be easier to manage while traveling on the mountain.

SNOWPACK: Two periods of rain and warm temperatures in January, one starting the 10th and one starting the 23rd, changed the snowpack drastically. Until yesterday and last night, very little snow has fallen on the mountain, leaving the knife hard, ice glazed surface the dominant feature. New wind slab will be forming on this ice glazed surface as well as on thin wind slabs that were scattered around in the terrain. Those wind slab appeared to be reactive at the upper interface 25 cm down in one pit in Left Gully but was well bonded to the icy surface in the same pit. No avalanches were reported on in either of those layers. Due to the light density (6.5%) of snow in the past 24 hours, it is likely that many areas will be scoured down to the icy bed surface later today but not before passing through a period of peak instability when wind slabs will be most sensitive to a human trigger, with sluffing and potentially some natural avalanche activity.

Microspikes and crampons are key tools for travel again today. Crampons are needed on the steeper slopes and above treeline. Conditions on the Sherburne Ski Trail is dust on crust with embedded rocks here and there.

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 or Harvard Cabin.
• Posted 8:00 a.m., Friday, February 2, 2018. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-2-2