Avalanche Advisory for Monday, March 27, 2017

This advisory expires at Midnight.

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger today. Central Gully has Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions exist. All other forecast areas have Moderate avalanche danger. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully to identify features of concern.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger today. The Sluice and Lip have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions exist. All other forecast areas have Moderate avalanche danger. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully to identify features of concern. The 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: Today, wind slab will be stressed by additional precipitation and will possibly become saturated, creating wet slab and wet loose avalanche problems. The hazard will increase through the day as the amount of precipitation and temperature increases. This avalanche problem is notorious for its unpredictability and today will be no exception. Looking at the amount of water arriving today, it will likely be at most half an inch by midnight. This is not a huge amount of liquid and combined with the ambient air temperature, may not be enough to overwhelm the cohesiveness of the slab. The areas of greatest concern today are rated Considerable due to the larger possible size of an avalanche as well as the steepness of the slope. Moderate rated areas could have similar but smaller avalanches that could be equally dangerous depending on the terrain.

WEATHER: Starting late in the evening on Sunday, the temperature began flirting with the freezing mark and currently sits at 30F at 6288’ with 40F at 4000’. A three hour period of precipitation, mostly freezing rain, overnight delivered 0.08” of water. After a brief break, precipitation is now falling again and should continue to fall through most of the day in some form. With the temperature remaining around freezing for the day, this precipitation will be a mix of freezing rain, sleet, ice and maybe snow up high with closer to all rain at lower elevations. Wind today will gust briefly this morning to 60mph from the SW and then lower in speed and shift to the W by day’s end.

SNOWPACK: Wind slab that formed at the end of last week covers much of the old, icy bed surface. These wind slabs vary in thickness and hardness depending on the slope aspect. North and NE aspects tend to have more old surface showing, mixed with areas of firm wind slab. While moving through E to S facing aspects, this wind slab is softer and more widespread. Today, all snow will be subjected to various forms of precipitation. It seems likely we may see close to 0.3” of water by early afternoon with a total SWE of 0.5” by the time this advisory expires. As the water percolates into the snowpack, the interface of the wind slab and old surface may become lubricated. This scenario playing out will create wet slabs that are very hard to predict. It is unlikely that the amount of precipitation combined with the temperature today will be enough to create widespread deep instability, but the new load on weak, thin slabs containing loose snow pellets that are poorly bonded to firmer slabs beneath will create plenty of cause for concern in many areas.

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 Harvard Cabin.

Posted 8:11 a.m., Monday, March 27, 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

2017-03-27