This advisory expires tonight at 12:00 midnight.
Tuckerman Ravine has Considerable and Moderate avalanche danger. Sluice, Lip, Center Bowl, Chute and Lower Snowfields have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Lobster Claw, Right Gully, Left Gully and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.
Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, Odell, South and Escape Hatch have Moderate avalanche danger. Evaluate snow, weather and terrain carefully. North, Damnation and Yale have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.
AVALANCHE PROBLEM: Wind Slabs developing today, in some areas on an already poor snow structure, are the primary problem. With the exception of the Lip, which was raked down to the bed surface yesterday, Considerable rated areas contain the largest expanses of older wind slab going into today’s weather event. This wind slab was reactive to human triggers yesterday and is most likely still reactive. South facing gullies in both Ravines, though still containing pockets of the older wind slab, benefitted from a period of settlement yesterday due to warming and, in Tuckerman, was also cut up by ski traffic.
WEATHER: Wintry weather continues as a cold front pushes through today bringing some moisture and wind to the region. The main weather factor affecting stability will be the wind. Currently, west winds in the 50 mph range are pushing some snow into east aspects. The wind is expected to pick to the 50-70 mph range later today. These wind speeds are the highest since roughly 6” of snow fell late last week which means that there is enough snow laying around higher terrain to provide the building blocks for new hard wind slabs. Light snow and snow showers through the afternoon hours may contribute 1-3” more snow to the slab building process.
SNOWPACK: Avalanche danger is starting out one rating lower in each forecast area that isn’t already rated Low. The above ratings are based on wind transported snow, plus 1-3” of new snow falling today, which will cause danger to rise.
A crown profile in the 50cm x 20m natural avalanche in the Lower Snowfields revealed that the failure layer of the slab was within soft (4F) snow and rimed snow particles. The overlying harder slab (1F) was softer than we often see due to the light winds that built it being only around 40 mph. This crown thickness and structure is very similar to that in the much larger Lip avalanche and is the same as you might find in other slopes and gullies, only in varying thicknesses and distribution. In summary, signs of recent avalanche activity in the previous 24-48 hours are one red flag to consider today. Another is active wind loading, as evidenced by snow moving along the ground at the ridgetop and above treeline, A third is a small amount of new snow and a weather forecast that includes wind speeds capable of moving that snow and building wind slabs. It’s pretty hard to miss these signs today, so if you choose to enter avalanche terrain, do so very carefully and limit time spent in avalanche runouts or, better yet, avoid them entirely.
- 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 8:16 a.m. Monday, March 30, 2015. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713