Avalanche Advisory for Friday, March 17, 2017

This advisory expires at Midnight.

Huntington Ravine has MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, Chute, Left and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

 AVALANCHE PROBLEM: Densely packed, wind transported snow has built wind slab over a softer layer of loose snow over the past 48 hours. Due to the potential size of these slabs and the challenges posed by avoiding them, they are the primary avalanche problem in moderate rated areas today. While these slabs may propagate a crack, the strength of the firm slab above makes these slabs very stubborn. This type of wind slab is most concentrated in areas in the lee of a northwest wind such as just beneath the ice in Center Bowl, below the rollover in the Lip and high in Chute. Central Gully appears to have an area of this firm slab, as well. In addition to the primary firm, wind slab problem, softer pockets of wind slab exist here and there in both Ravines but are much smaller and discontinuous so shouldn’t pose too much of a challenge to avoid. Hillman’s and Left Gully are on the low end of the moderate rating due to more areas being scoured. Evaluate snow and terrain carefully today.

WEATHER: Around 2.5” of new snow fell on the summit in the past 24 hours on strong west and west-northwest winds. Winds remain strong from this direction after blowing in the 60-75 mph range during most of the past 24 hours. No new snow is in the forecast today and summit fog is slowly clearing now. Expect mostly sunny skies and cold temperatures, currently -8F, rising to just above 5F today with moderating wind from the NW in the 30-45 mph range.

SNOWPACK: More field time yesterday revealed the wind-scouring action of recent high wind speeds. Most of the softer and more sensitive wind slabs that remained after the passage of the last nor’easter were either ripped up and blown away or bridged over by firm, pencil hardness new wind slabs. Pockets of smooth wind slabs exist in some areas and while there is a softer layer beneath, the bridging power of the overlying firm slab allowed us safe passage yesterday on the slope between Lobster Claw and Right. Of equal or even greater concern than the areas of stubborn wind slab in the terrain is the widespread ice crust that is exposed after the hammering winds over the past weeks. The old adage that the “leader must not fall” is applicable on this surface since you would be fooling yourself to think that self-arrest is possible on this surface in steep terrain. Careful route-finding, roping up and/or not falling are key on our above this surface. A race tune on your backcountry skis could also be helpful.

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 the Harvard Cabin.

Posted 8:15 a.m., Friday, March 17, 2017. 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

2017-03-17