Avalanche Advisory for Wednesday, March 15, 2017

This advisory expires at Midnight.

 

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, Odell, South and Escape Hatch have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Danger avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential. North, Damnation, and Yale Gully have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully.

Tuckerman Ravine has CONSIDERABLE avalanche danger. All forecast areas 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. The exception to this is the Little Headwall which has Low avalanche danger. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Wind Slab developed in all avalanche terrain yesterday and last night. As winds were strong and blew from many directions, the wind slab does not appear to be thick, but exists on most aspects and can be found primarily in the bottom and mid-elevations of forecast areas. As the wind increases this afternoon, avalanche danger will increase and may push the upper end of the current rating by midnight. The danger will also increase when the forecast 2-4” of snow arrives. If the total is closer to 4”, we could exceed our current ratings on lee slopes of west and northwest winds.

WEATHER: Yesterday’s nor’easter delivered 19.2” of snow with a liquid equivalent (SWE) of 1.5”. Winds blew strong during the course of this storm, starting from the SE and moving to the E during the heaviest snowfall periods with steady speeds of 100mph. At midnight, the wind continued its counter-clockwise rotation through the NE and speeds dropped sharply to 15mph. It was around this time that the snow stopped as well. Since midnight, winds moved to the W and are currently 27mph. Today, winds will shift between the W and NW, slowly increasing as the day progresses. Wind speed should top 50mph by late afternoon. Skies are clear this morning, but with moisture still lingering to the west that should move in this morning, summits will return to intermittent fog and occasional snow showers, bringing 2-4” through the day. Tonight, as winds move to the NW and increase to 60-80mph, another 1-3” of snow may arrive.

SNOWPACK: Wind slab from various storms over the past week sits on top of a solidly frozen snowpack. Prior to yesterday, the largest pockets of wind slab resided in the Lip and Center Bowl area of Tuckerman. Snow that fell yesterday was subjected to strong winds from multiple directions for much of the day. This resulted in slopes loading from all directions. The wind slab that formed yesterday will likely have many layers and minute density changes within, creating many interfaces to possibly fail on. Due to cross-loading, north and east-facing slopes contain connected wind slab for much of the forecast area. South-facing slopes were scoured by winds at the top, but contain areas of wind slab in the bottom of these forecast areas. Signs of avalanche activity yesterday can be found, although it appears most fractures were on the smaller side and have since reloaded. As snow starts today and winds increase from the W and NW, significant loading will take place on east-facing slopes. With most of yesterday’s snow still clinging to slopes, avalanche activity tonight may be on the larger side.

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 8:40 a.m., Wednesday, March 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) 466-2856

2017-03-15