Mar 302015
 

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.

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 8:16 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

2015-03-30

Mar 292015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable, Moderate, and Low avalanche danger. Dangerous avalanche conditions exist. The Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The Sluice and Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Lobster Claw, Right Gully, Left Gully, and Hillman’s Highway, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

Huntington Ravine has Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: Wind slabs are the primary avalanche threat today. The main driver behind the Considerable rating for some areas is the low drifting snow currently cascading down steep slopes. This slow loading has caused good-sized avalanches in the past, even on bluebird days like today. It is taking place in the Sluice as well, though as a slightly lesser rate. The Lower Snowfields contains snow with varying levels of stability. I expect the worst to be tight under the rock buttresses. Left Gully and Hillman’s have pockets of new snow loaded into isolated terrain features. Although posted at Low, they may contain unstable snow capable of producing an avalanche. It ain’t spring yet, folks, regardless of what the calendar says.

WEATHER: Blue skies will dominate today, but it will feel more like a nice day in February than the end of March. Expect temperatures below normal. Even south-facing slopes may not get enough heat to moisten the uppermost snow. Westerly winds around 30-40mph will have two noticeable effects. One is to generate additional wind loading, particularly low drifting snow in the center of Tuckerman. The other is to suck the heat away from the snow in south facing slopes, making it harder for the sun to soften the surface. Over the last four days, Mt. Washington has received about 7” of new light density snow, which is at the center of our avalanche concerns.

SNOWPACK: I wrestled with the ratings for Tuckerman today and decided on the higher rating of Considerable for locations where there currently is snow drifting down over the headwall. Today would not be the first time I’ve seen a seemingly small amount of loading trigger an avalanche. I’ll caution you all that as long as this is going on, you will want to be extra cautious. This means that even going into the floor of Tuckerman to access a Low rated area will put you at risk. If it shuts off completely, we’ll be left with a human trigger problem rather than a natural trigger problem. Although this isn’t ideal for recreation, it’s more manageable.

In Lobster, Right Gully, Left Gully, and Hillman’s, the majority of the surface snow is old and stable. However, there are locations where you may find unstable snow, such as the skiers’ left side of Left Gully or hard on the skiers’ left side of Hillman’s. Other examples may exist, too. You’ll need to be alert for these pockets, assess their stability, and determine whether or not you want to pass through them. You may also need to make a decision whether or not you want to be below someone who is making a similar decision!

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 8:23 a.m. Sunday, March 29, 2015. A new advisory will be issued tomorrow.

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

2015-03-29

 Posted by at 8:22 am