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Sun, January 27th, 2013 - 7:00AM
Mon, January 28th, 2013 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

A MODERATE danger continues above treeline for wind slab and deep slab avalanches. Northwest winds will continue to form wind slabs on leeward slopes that will be possible for a person to trigger today. These will be most likely found in the steeper terrain and in cross-loaded gullies and sub-ridges. Additionally, there remains the possibility of triggering a deeper and more dangerous avalanche, most pronounced on steep slopes with a shallow snow cover. There is a LOW danger below treeline where a stout crust exists on the surface.

Sun, January 27th, 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

Yesterday, the cold and sustained NW wind not only affected the ridgetops but also penetrated down to treeline in some locations. This allowed for wind slabs to form both on and off the ridgelines. These were on various aspects as the wind was being channeled in many directions by the terrain. A few of these 6-12″ slabs were triggered yesterday by people but were confined to the steeper terrain (around 40 degrees or more).

Today we should see more the same. The cold NW wind continues and though there will be less snow available for transport, we should still see shallow slabs forming. Most of these are likely to be a bit sluggish on slopes around 35 degrees but in steeper terrain expect them to release and pack more of a punch. These slabs can become quite serious in committing terrain if, for example, one gets dragged over a cliff or caught and covered in a terrain trap. Watching for current wind loading, stiff or hollow feeling snow that may crack around you will be signs you have found a wind slab. Also, watch for cross-loading in gullies and sub-ridges as these winds have been blowing well below the ridgetops during the past 24 hours.

As far as the snow surface conditions go, they are highly variable with significant wind affect at most elevations. Soft powder can still be found among the wind hardened surfaces in the more sheltered locations above 2,000’. Mostly supportable crusty conditions exist below 2,000’.

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 freeze over us again today is helping considerably to “lock” in the snowpack as a whole (except for the wind slab problem discussed above). However, we are still concerned that in shallow areas above treeline there remains a chance a person could trigger a slab avalanche breaking near the ground. Keeping with good travel practices – exposing only one person at a time, moving efficiently through steep terrain and steering clear of trigger points such as shallow areas near rocks will be your best bet for avoiding one of these larger and more dangerous slides.


Sun, January 27th, 2013

If you thought yesterday was a cold one, just wait for today… We have fallen – literally – off the charts for temperature at many ridgetop locations. Our Friends weather stations are reporting near or below -10F at all locations this morning while lower elevations are slightly warmer in the -5 to +5 range. Temperature will continue to decrease another few degrees over the course of the day.   But, skies are clear and the sun will be out!   Wind? It was in the bothersome range on the ridgelines yesterday (NW @ 10mph gusting 25mph) and has picked up slightly this morning (predominantly NW @ ~15mph gusting 35mph). Good frostbite weather.

Tomorrow temperatures should bounce back to a more civilized range as winds shift back to the SE bringing clouds and warmer air ahead of a large low pressure system pushing into the Gulf. Snow flurries are in the forecast for Monday night into Tuesday with a better chance for accumulation on Wednesday.

Fitz will issue our next advisory tomorrow morning, January 28th.

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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.