This advisory expires at Midnight.
Huntington and Tuckerman Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches likely. The only exception is the Little Headwall in Tuckerman Ravine which has Low avalanche danger. Natural and human-triggered avalanches are unlikely there. Open water and thin coverage exist there in spots.
AVALANCHE PROBLEM: Storm slab, from the 10” of dense, new snow recorded on the summit in the past 24 hours, and wind slab, due to cross-loading and direct loading of some terrain features, will make human triggered avalanches likely this morning in steep terrain. Snow, ice pellets and some freezing drizzle overnight created an “upside down”, or increasingly dense snowpack, due to warming temperatures. Last night’s precipitation will add to instabilities that were observed yesterday afternoon when test slopes were propagating cracks. In the steepest terrain today, any new precipitation especially combined with warm morning temperatures, will make the wind slabs and storm slabs unstable, creating dangerous avalanche conditions. Dense fog will reduce visibility and make safe travel options and visual assessment challenging.
WEATHER: Yesterday, a winter storm brought significant snowfall on SE wind of up to 60 mph in our forecast areas. Currently 26F on the summit, temperatures are forecast to mimic yesterday’s high of 29F indicating that the ravines could warm above the freezing mark today. Cloud cover should persist, limiting any solar warming of our snowpack. Current summit wind of 30 mph from the west will decrease and shift to blow from the NW throughout the day, making further wind loading unlikely.
SNOWPACK: Although it’s April, winter weather continues to provide a dynamic snowpack. Storm total snowfall of 7” at Hermit Lake and over 10” on the summit has been transported by a predominantly SE wind that held at over 50 mph on the summit during daylight hours yesterday. Terrain-driven wind varied in direction low in the ravines. Accordingly, the new snow that is our primary layer of concern is variable in character across our terrain. Areas lee to a SE wind should hold the greatest instability, but don’t discount others that likely also hold a cohesive slab. Prior to yesterday, several days of a melt-freeze cycle created a breakable crust across our terrain, with the exception being isolated pockets which were fully shaded through Sunday and Monday. We don’t expect an avalanche in the surface snow to step down and release a deeper slab, but this possibility is not entirely eliminated. Continual observation and stability assessment is particularly crucial for any traveler in avalanche terrain today. Keep our current spatially variable storm snow in mind, remembering that your stability tests could yield very different results in close proximity to each other.
• 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 8:20a.m., Wednesday, April 5, 2017. A new advisory will be issued tomorrow.
Frank Carus/Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856