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Tue, February 25th, 2014 - 7:00AM
Wed, February 26th, 2014 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

There is a MODERATE avalanche danger for triggering a slab avalanche between 1 and 3′ deep. Persistent slab avalanches up to 3′ in depth remain possible for a person or snowmachine to trigger on steep, 40deg+ slopes, with prior wind loading. Also, watch for lingering hard wind slabs in steep rocky terrain around a foot deep that formed during Sunday’s wind event. And last, with warming temperatures at the upper elevations today, watch for cornices to become more sensitive and potentially break.

Tue, February 25th, 2014
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

It was a fairly quiet day in the backcountry yesterday. Not many folks were out (possibly due to the challenging surface conditions) and no avalanche activity was observed/reported.

For today, triggering a persistent slab avalanche is the primary concern. Sitting around 1-3′ deep in the pack is a thin layer of weak faceted snow on top of a thick crust that has plagued our mountains for over 2 weeks. Though the likelihood of triggering one of these has decreased, the consequences have increased. The slab is now hard (due to Sunday’s wind) and will likely allow a person and/or sled onto it before potentially releasing – making escape more difficult. The most likely areas to trigger a persistent slab are steep wind loaded slopes (>40deg) that are unsupported from below. Additionally, keep in mind those likely trigger points. These are where the slab is thin: near rocks, on the tops of rollovers and the edges of Sunday’s wind slabs/drifts.

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

It seems there was very little snow that the strong winds on Sunday did not move around to some degree. Current surface conditions are everything from scoured ground, sastrugi, hard wind slabs/drifts and even some soft settled snow in between and in the trees. Wind slabs yesterday were very hard, variable in distribution and stubborn. They seem to be fairly well welded into place – generally speaking. However, in steeper rocky areas where the slabs are unsupported from below or they are resting on weak faceted snow I’d be suspect one could be triggered.

Additional Concern
  • Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

As temperatures begin to climb today with the approach of warm air at the upper elevations, watch for cornices to become more sensitive.  They are composed of very hard snow right now and could break farther back than expected.

Tue, February 25th, 2014

During the past 24-hours we have seen clear skies and breezy winds. Temperatures rose to the mid 30’s F at treeline yesterday and the low 20’s F on the peaks. Valley bottoms have cooled off overnight and are sitting in the teens this morning as ridgetops remain around 20F. The South and Easterly winds continue to average between 10-20mph with gusts up to 53 overnight.

Today we have one more sunny and breezy day on tap. We should see daytime highs in the mid 20’s on the peaks and around 30F at treeline. Southeast winds remain around 10-20mph with higher gusts but should increase tonight. Cloud cover will also increase late in the day as a warm and wet storm approaches.

Yes, a warm storm system is on our doorstep. Beginning tonight and through Thursday we can expect temperatures to rise significantly with a chance for decent precipitation. Models now are showing around 1″ of water equivalent from tonight through Thursday with a rain/snow line ~1-1,500′ (but may be higher..). Stay tuned – this could go one way or the other as is common for AK!

An inch of water – equating to a foot or so of snow – would help mend the ski and riding conditions which now look a bit like this:

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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.