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Sun, December 2nd, 2012 - 7:00AM
Mon, December 3rd, 2012 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

Due to inadequate snow conditions and to prevent resource damage, operating or possessing a snowmobile on or within the Seward and Glacier Ranger Districts of the Chugach National Forest is prohibited until further notice.  You can view the official Forest Order for this closure HERE.

We continue to have a MODERATE avalanche danger today above treeline for persistent slab avalanches. The possibility remains that a person could trigger a slab breaking near the ground on steep slopes above 3000ft. As the snowpack, and remaining slabs, continue to deteriorate under cold and clear weather, loose snow sluffing is becoming more prevalent. Below treeline there is a LOW avalanche danger.

This Bottom Line will pertain to Monday, December 3rd, as well.

Sun, December 2nd, 2012
Above 2,500'
2 - Moderate
Avalanche risk
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Another sunny and cold day will continue to slowly reduce our persistent avalanche problem. We are still receiving reports of collapsing in the snowpack from folks getting off the beaten path into untracked, upper elevation areas which points directly to lingering slabs that can still be triggered by a person if the slope is steep enough. It is these areas we are most concerned with and that keep our danger above treeline at MODERATE.

That said, the majority of the terrain where people have been recreating lately is lacking a slab and the 2-3’ of snow cover consists mostly of various layers of weak, unsupportable snow. There has been a little too much P-Tex left out there not to my, or I believe anyone’s, liking.

As far as the surface conditions go, there is still plenty of soft “square powder” in wind sheltered locations. However, the past few days saw enough wind to form a thin, breakable crust in higher elevation exposed areas – not helping to improve the riding conditions and something to keep in mind with any new snow as the thin crust sits on very weak near surface facets. Surface hoar is anywhere between nonexistent up to 1cm above treeline but is growing some very large and impressive feathers in the creek bottoms.

As powder starved as we are right now, and with the hope of a shift in the weather for precip in the next week, we need to remember that our snowpack from top to bottom is full of weak layers. To use Kevin’s “tent” analogy from yesterday, the tent is made of any of the following weaknesses from the peaks down to sea level: facets, surface hoar, near surface facets, depth hoar and crust/facet sandwiches. Things could get quite interesting very quickly avalanche wise once the snow finally does head our way.

Sun, December 2nd, 2012

This will be the 13th day in a row where sub-zero temperatures plague the lower elevations and parking lots in response to a region-wide inversion under clear skies. This morning is one the coldest so far: -21F in Portage (10ft above sea level) and warming with elevation to only +10F at the Sunburst weather station (3812ft). The good news is the wind has stayed fairly well behaved. Ridgetop winds switched around to the NW and W yesterday and are blowing around 5mph with gusts to 10mph currently, this is where they are expected to remain through the day.

It still looks like we could get a large scale pattern shift this coming week and a possible flurry or two Wednesday and Thursday with hopefully more soon after that. We should have a much better handle on this for Tuesday’s forecast so stay tuned.

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).  

I will issue the next advisory Tuesday morning, December 4th.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.