Avalanche Advisory for Sunday, February 11, 2018

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central and Pinnacle gullies have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully to identify features of concern.

 Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully to identify features of concern.  The Little Headwall is the exception with Low avalanche danger. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Existing wind slabs formed late last week will be stressed by added moisture and warmth from our current weather and are becoming wet slabs. By either name, these relatively soft slabs that a human could likely trigger should lose stability through the day. Areas of greatest concern due to size of soft slabs on the surface are the Headwall area in Tuckerman and Central and Pinnacle Gullies in Huntington. Realize that moderate rated areas likely hold this same slab that while smaller could still produce an avalanche capable of burying you. Wet loose sluffs that you could initiate in steep, soft snow that is less cohesive are also a significant concern. The risk of travelling on or below avalanche terrain might not be worth the reward on a damp day like today.

 WEATHER: It’s become warm and wet, but we shouldn’t see enough warm precipitation to drastically alter snow coverage. Yesterday and last night saw predominantly above freezing temperatures in our terrain with a few inches of moist new snow and mixed precipitation totaling 0.25-0.5 inches of liquid water (SWE). Today will be slightly warmer, remaining above freezing at Hermit Lake and possibly exceeding 32F on the summit as well. Mixed precipitation today should total less than 0.25 inches of liquid water (SWE). Tomorrow will be colder with no forecast precipitation, forming a crust of our currently moist snow surface.

SNOWPACK: A series of storms with wind over the past week allowed significant new wind slabs to develop and produce natural avalanches. Our snow surface which is becoming increasingly moist varies from soft to hard slab, with the melt/freeze crust formed mid-January exposed in small wind-scoured areas. The primary stability concern today is the weakening of our softer surface snow by moisture and warm temperatures. Considerable rated areas which have generally more cohesive slabs could produce large avalanches, and you could easily initiate a significant loose wet sluff in steeper snow that is less cohesive. We don’t expect human triggered avalanches to be likely in areas with firmer surface slabs, though our upper snowpack will generally lose strength until a refreeze occurs late tonight or tomorrow.

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 8:15 a.m., Sunday, February 11, 2018. 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

2018-2-11