Avalanche Advisory for Thursday, February 4, 2016

All forecast areas of Tuckerman and Huntington Ravine currently 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, Lower Snowfields, and the Little Headwall in Tuckerman Ravine and North, Damnation, Yale and the Escape Hatch in Huntington Ravine are not posted due to lack of snow cover. Exercise caution in these areas and expect the potential for isolated patches of instability in larger snowfields.

 AVALANCHE PROBLEM: Deep Persistent Slab is the primary avalanche problem today. Wet snow and sleet, followed by rain penetrating the snow with continued warm temperatures overnight, has potentially weakened buried weak layers.  This could trigger a larger avalanche in some terrain. This is an exceptionally difficult avalanche problem to assess in the field since there are so many variables involved but it would be a good idea to assume a larger avalanche could run this morning from those areas with the greatest amount of snow. Be wary of a similar issue in the few areas of Huntington which have a significant amount of snowpack remaining. This problem will diminish through the day as colder air moves into the region and refreezes the snowpack.  Expect a Low rating by day’s end as free water in the snow stops flowing and the surface begins freezing.

WEATHER: Current temperature at Pinkham Notch is a balmy and damp 46F with calm winds. On the summit, southwest winds in the 50mph range have begun to shift to the West.  It will remain from this direction and decrease today as a cold front moves through and stalls to the east of the region. Temperatures will fall into the upper teen’s F on the summit, from their current position in the upper 20’s F, while remaining moisture may produce a few snow showers.

SNOWPACK: The warm and rainy conditions over the past 24 hours are the primary driver of today’s avalanche rating. Though the summit recorded 2” of snow at the beginning of yesterday’s storm, that snow has been hammered down by the sleet and rain that followed.  A half inch (1.25cm) of total snow water equivalent fell which combined with melting snow to percolate into our snow pack. Since surface instabilities more than likely peaked sometime overnight, it is the deeper, weak layers that are our primary concern. The firm wind slab that dominated our upper snowpack prior to this storm has undoubtedly weakened by all the penetrating heat. Given the variability in the strength and thickness of the surface slab, the variability of distribution of the two main facet layers near the basal ice crust, and near a higher melt freeze crust, it is really hard to predict when, or even if, the upper slab layers will fail naturally. The destructive power of a resulting wet slab is partially driving today’s rating rather than the certainty of a natural avalanche. In either case, expect a punchy snowpack when booting with plenty of water flowing over and beneath ice pitches so travel cautiously in both Ravines if you travel at all.

The Lion Head Winter Route is open and is recommended for those opting to avoid avalanche terrain in the early season. Microspikes and ski poles are helpful on lower elevation trails, but are not substitutes for crampons and an ice axe on this route. The John Sherburne Ski Trail is more than likely impassable on skis after last night’s rain and warm temperatures.

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 8:20a.m. February 4, 2016. 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

2016-02-04