This advisory expires at 12:00 midnight.
Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential. Lobster Claw, the Lower Snowfields, and Little Headwall are not posted due to a lack of snow in these areas.
AVALANCHE PROBLEM: Today’s main avalanche concern is Wind Slab from snow late last week as well as new wind slab developing today. The day started with instability primarily in Chute through Sluice and Central in Huntington. As forecasted snow materializes today, new wind slab will form, increasing the size and potential of avalanches, including the potential for avalanches to step down into deeper weak layers in areas listed above areas and run far onto the floor of Tuckerman Ravine. Safe travel in avalanche terrain today will require keeping track of new snow and increasing wind speeds as these two factors will increase the hazard as the day progresses.
WEATHER: Six inches of snow fell late last week on west winds that stayed strong through Saturday evening creating the current instability. Calm winds and sunny skies on Sunday allowed some warming, but not enough to reach down to existing weak layers and improve stability. As today progresses, temperatures will drop and west winds will shift northwest, increasing to ideal loading speeds. Forecasted snow totals for the day are 1-3″ and possibly another 1-2″ tonight. Expect reduced visibility due to snow and low clouds today.
SNOWPACK: The snowpack hit the reset button on March 16. After that time, wind slab, due to six inches of snow and strong west winds, formed in lee areas. Field time yesterday in Sluice and Chute provided valuable information. Compression tests on 60cm of new snow in the Chute failed just above the old surface on CT14 shear of Q1. The surface snow was 20cm of pencil hardness sitting on top of 40cm of on finger (1F). The column failed on a thin layer of heavily rimed particles and graupel people are finding in many places around the ravines. On the sunny side of the bowl, a thin layer of facets had developed just above the crust due to the dramatic diurnal temperature fluctuations. I expect that these have continued to grow last night and into today. Careful ski cuts in the upper Sluice produced a 15′ by 15′ 4-6″ thick slab.
Weather today will increase the instability. New snow and winds increasing from the W and N will form wind slab on top of the current snowpack. Crown lines in Chute and Center Bowl from Friday were visible over the weekend, however it appears Lip and Sluice did not avalanche in the cycle. As snow falls and winds increase loading these aspects, I would be very wary of traveling in or under these slopes. If attempting travel in avalanche terrain today, the hazard will be hard to mitigate due to the increasing potential as well as limited visibility.
- The Tuckerman Ravine Trail uphill from Pinkham to Hermit Lake is mostly wall-to-wall ice covered with the layer of new snow. Traction devices or crampons are necessary for reasonable travel on this trail.
- The Lion Head Summer Trail is open. The winter route is now closed.
- The Sherburne Trail is closed about 2/3 mile up from the parking lot. Please respect the closure by walking over to the Tucks trail at the rope to reduce erosion on the ski trail.
- 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 8:30a.m., Monday, March 21, 2016. A new advisory will be issued tomorrow.
Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716