Jeff

USFS Snow Ranger since 2005.

Dec 162014
 

This advisory expires tonight at 12:00 midnight.

All forecast areas of Tuckerman and Huntington Ravine have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features which may be capable of producing small avalanches.

AVALANCHE PROBLEM: Today’s avalanche problems will be any lingering pockets of wind slab or small wet slabs, depending on how quickly and how far temperatures drop during the day today. Low danger means conditions are generally safe, but it includes the possibility for unstable snow in isolated terrain features or in extreme terrain. In the current early season snowpack, pretty much all the snowfields except for a few can be considered “isolated terrain features” or “extreme terrain.” Wind slabs that developed this past Sunday have had time to stabilize, but I won’t rule out the potential for some instabilities to still be found out there, particularly in areas such as the Lip, Center Bowl, or Central Gully.

WEATHER: Yesterday the Mt. Washington Observatory recorded a max temperature of 41 degrees F (5C) and stayed above freezing for most of day and overnight. Temperatures at Pinkham Notch were down below freezing during this same period. Today we are expecting temperatures to drop slightly at the upper elevations. Increasing clouds will foreshadow a weather system moving in later tonight and sticking around until early Thursday. Keep your eyes on the summits weather forecasts if you are planning a trip for Wednesday or Thursday.

SNOWPACK: A prominent player in the snowpack discussion today is the elevation of the warm/cold line and, more importantly, just how warm the snowpack in the ravines in the last 24 hours. In this case, I would expect that warmth entering the snowpack has worked toward stabilization of previously existing wind slabs. If these became very warm and saturated wet, then the trend might have worked in the opposite direction as there would be a wet slab sitting on top of an ice crust or in some locations plain water ice, hence the discussion about the potential for pockets of unstable slab in isolated terrain features. I don’t want to get too bogged down in the nuances of warmth on snow, because I’m hopeful that falling temperatures will continue to strengthen the snowpack to where we will sit solidly in Low danger before long. Until lock-up happens, you should expect to find generally good stability with the potential for some small unstable slabs.

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 7:50 a.m. December 16, 2014. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-12-16

 Posted by at 7:49 am
Dec 152014
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has MODERATE and LOW avalanche danger. The Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Lobster Claw, Right Gully, the Sluice, Left Gully, and Hillman’s Highway have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features. Lower Snowfields and the Little Headwall are not posted due to lack of snow cover.

Huntington Ravine has MODERATE and LOW avalanche danger. North, Damnation, Yale, and Central have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Pinnacle, Odell, South Gully, and Escape Hatch have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: Wind slab is the avalanche problem you are most likely to see today. For the most part, the terrain in the ravines is very discontinuous at this point early in the season. There are some larger snowfields with more continuous snow cover, but in most forecast areas you will be moving from one distinct patch of snow to another. This requires ongoing assessment of snow stability and solid route-finding skills to keep you away from unstable snow. Many areas posted at Low danger do have wind slabs that may be unstable. The primary differentiating factors between the Moderate rated locations and the Low rated areas are the size and distribution of the slab, not necessarily the likelihood of you triggering the snow.

WEATHER: If you are a fan of mild weather, today is your day. Temperatures will be rising above freezing all the way up to the summit while winds diminish to a gentle 5-20mph from the NW (Beaufort 3-4 for the nautical-minded). Warmth will persist through the night, until temperatures begin to fall back on Tuesday in advance of a weak weather system mid-week.

SNOWPACK: As already mentioned, one defining characteristic of the current snowpack is that it is very broken up. There are few large connected snowfields, which means that any avalanche that is triggered will be relatively small but can be quite dangerous. Areas posted at Low have more options for avoiding instabilities than those rated Moderate. In these conditions it can be quite tempting to take the “easier” route through the snow rather than the “safer” route that avoids instabilities, but I’d recommend choosing the less hazardous route unless you can confidently say that the snow has good stability.

Yesterday I spent some time in Tuckerman looking at the snow structure. What I found would be very disturbing if the ravine was more filled in than it currently is, and is certainly disturbing when found in exposed areas like the Lip or Center Bowl. There is slab at the surface that was formed during Sunday’s winds. This sits on top of a layer of light unconsolidated snow (read: weak snow). Beneath this is a sleet crust and other crusts. Stability tests at our location provided very easy results – CT0, CT0, ECTP4 – at the interface between the uppermost slab and the weak snow. As the columns popped off the pit wall, the weak snow layer was left intact on top of the crust. You should expect the depth of these layers to be quite variable as you move from one location to another.

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 8:15 a.m. December 15, 2014. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-12-15

 Posted by at 8:11 am