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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 28th, 2013 - 7:00AM
Expires
Tue, January 29th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE above treeline today, where wind slabs will become more sensitive to human triggers with a slight rise in temperatures.   Deep slab avalanches are still a concern above treeline as well.   Below treeline the hazard is LOW, where recent cold temperatures have helped to solidify much of the snowpack.

Mon, January 28th, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
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. Dangerous avalanche conditions. 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

Wind slabs formed over the past several days of sustained light to moderate winds are the primary concern today.  Look for these slabs to be relatively shallow, less than a foot in depth and sitting in potentially unusual areas (e.g. mid slope, well below and away from ridgelines).  Recent winds have created shallow slabs that were sensitive to human triggers over the last two days.  In the higher elevations much of the snow that was available for transport has been either scoured or turned into these stiff slabs.  The chance of new wind slabs forming today are on the low end because of this lack of snow available for transport.  The wind slabs we observed being triggered this weekend pulled out in steeper terrain, generally above 35 degrees and on average closer to 40 degrees.  A rise in temperatures today will increase the sensitivity of these slabs.  Be on the lookout today for these pockets of lingering slabs, especially above cliffbands, gullies and trees.  While these avalanches are generally low in volume, consequences go up when one of these pockets sweeps you into or over a terrain trap.

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 problem continues to linger.  This problem has gone from being a widespread issue to one that exists primarily above treeline.  Warm temps and light rain last week melted the snow surface and penetrated to the lower layers of the snowpack.  These melted layers have now had time to go into a hard freeze and are much stronger.  Above ~2,000′ this process has not occurred to the same extent.  Therefore, it is worth remembering that the weak snow that formed in the beginning of the season still lurks below.  The likelihood of triggering a deep slab today is low.  The consequences of triggering an avalanche in weak layers buried 3-8 feet deep are still potentially high.

Weather
Mon, January 28th, 2013

Clear and cold conditions dominated the region over the weekend.   The Sunburst weather station at 3,800′ reached -17 degrees F overnight.   Winds have been light to moderate during this time, primarily out of the North, Northwest and West.   No precip has fallen over the last several days.

Look for temps to begin climbing today as a low pressure system centered to South of the Aleutians makes its way towards South Central Alaska.   Temps will reach into the teens by midday, clouds will move in and just a trace of snow will fall during the day today.   Winds will shift from West to East and will be 10-15 mph with gusts to 30mph.

A greater chance for snow will come tonight and into tomorrow.   Temperatures will continue to rise into the 20s and 30s into the middle part of the week.   A chance of snow exists each of the next three days in our area.

___________________________________________________________________________________

Wendy will issue the next advisory tomorrow morning, January 29th.

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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.