Avalanche Advisory for Wednesday, February 15, 2017

This advisory expires at Midnight.

 

All forecast areas of Huntington and Tuckerman Ravine have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential today. The only exception to this is the Little Headwall which has Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: The avalanche problem this morning is Wind Slab. We are starting the day at the lower end of our Considerable rating, with some areas like the north walls of both ravines closer to Moderate. All areas have wind slab that formed from the Sunday-Monday storm that in places is quite thick and has a clear upside-down composition. As the day progresses and snow accumulates, we will see Storm Slab form and all areas move solidly into Considerable. As snow accumulates, be on the lookout for Loose Dry avalanches. By the time this advisory expires at midnight, many places like the Hillman’s, Left Gully, South and Odell will be pushing the higher end of the Considerable rating.

WEATHER: Twenty-four inches (24”) of snow fell Sunday afternoon into Monday. Winds shifted around the compass during this storm. After a clear day yesterday, snow showers began around midnight with just under an inch accumulating by this morning. Winds are currently from the S at 30mph and will remain there for most of the day, possibly shifting to the SW this afternoon before moving to the SE this evening. Snow showers will get heavier as the day continues, with up to a foot (12”) of new snow by tomorrow morning. Winds tonight will shift through the E to the N and increase to 45mph.

SNOWPACK: Widespread wind slab formed at the end of the previous storm. Several avalanche cycles have come and gone with most crowns refilling due to wind loading. In addition to the wind slab, large areas of debris exist in the approaches to gullies. Mid sections of some gullies that saw smaller avalanches are scoured down to the old breakable crust from last week, however, areas that had large and very large avalanches saw this crust ripped out and due to their more wind sheltered locations, are now loaded with large areas of wind slab. The upper portion of the wind slab was mostly fist to four-finger hardness (F-4F) with a potential failure layer of fist hard snow underneath. Snow today will arrive on south winds, allowing the southern gullies to see the most loading of new wind slab. As the past storm allowed many slide paths to run large and rarely formed paths to develop, approaching any gully in our terrain will now require crossing under several avalanche paths. Limited visibility today will create difficult safe navigation.

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  8:30 a.m., Wednesday, February 15, 2017. A new advisory will be issued tomorrow.

Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713

2017-02-15