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Tue, January 29th, 2013 - 7:00AM
Wed, January 30th, 2013 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

Above treeline, the addition of 2-4 inches of snow with sustained easterly wind will keep our avalanche danger at MODERATE today for wind slab avalanches. These will be most pronounced on upper elevation steep slopes and in the 4-12″ thick range. Watch for these fresh slabs to be sensitive to human triggers. Below treeline the danger remains LOW where only 1-3 inches of snow is expected to fall on a stout crust. It is unlikely, but in the case snowfall rates pick up and more than a few inches falls below treeline, expect the danger to rise to MODERATE as the new snow, and subsequent wind drifts, will not bond well to the crust.

Tue, January 29th, 2013
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
  • 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 was a fairly quiet day in the backcountry yesterday. We did not see or hear of any avalanche activity, nor were there too many folks out watching last weekend’s clear skies fill with clouds. We did get one report of soft wind slab conditions found in steeper north facing terrain.

Today, moderate to strong easterly winds accompanied by a few inches of snow is on tap. Fresh wind drifts and slabs will be forming on the lee side of ridgelines and in catchment zones mid-slope. These are likely to be sensitive to human triggers but in the shallow range (4-12”) due to the modest amount of new snow and the limited existing snow available for transport. Keeping an eye out for smooth rounded surfaces, stiff feeling snow and shooting cracks will be key to avoiding triggering a wind slab avalanche.

Below treeline a stout crust exists on the surface where the few inches of new snow today will likely get blown around and drifted into pockets. These pockets should be quite small but at the same note, will have a hard time sticking to the crust. In the case snowfall amounts increase to more than a few inches, watch for these small drifts to become larger and more worrisome.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

The deep slab avalanche problem remains in the back of our heads. We are still concerned that in shallow areas above treeline there is a chance a person could trigger a slab avalanche breaking in the weak snow near the ground. Keeping with good travel practices – exposing only one person at a time, moving efficiently through steep terrain and steering clear of shallow areas near rocks is the best bet for avoiding one of these larger and more dangerous slides.

Tue, January 29th, 2013

Cloudy skies, rapidly warming temperature and scattered snow showers have moved in overnight. This has quickly replaced the cold and clear weather that dominated the weekend. Overnight, Girdwood Valley and the Turnagain area picked up 1-2 € of low density snow but the snow showers are tapering off this morning. Temperature is on the rise at all elevations – ridgetops have gone from -10F to ~+10F in 24 hours while lower elevations have seen a jump from ~-15F to +15-25F. The easterly wind that is responsible for bringing in the warm air has been in the 10-20mph range gusting near 40mph.

Today, snow flurries will continue but look to only add another inch or two in favored locations – for a total of 2-4 € of new snow. Temperatures look to top out in the mid to upper teens at ridgetops today and the mid to upper 20’s below treeline. The easterly wind will remain in the 15mph range with gusts to 40mph.

Wednesday and Thursday will see cloudy skies, increasing temperature and a better shot for snow accumulation. We should see snow at sea level today but this will turn to a rain-snow mix Wednesday.

Kevin will issue the next advisory tomorrow morning, January 30th.

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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.