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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 25th, 2013 - 7:00AM
Expires
Sat, January 26th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE above treeline today, where human triggered avalanches are possible, especially in wind loaded starting zones.   Below treeline the hazard is LOW, where recent warm temps and subsequent freezing have helped to greatly minimize the likelihood of triggering avalanches.

Fri, January 25th, 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. 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

Look for older wind slabs to be lingering in pockets above treeline today.  Light to moderate winds will blow around a few inches of light density snow to also form new shallow wind slabs today. Yesterday my partner and I observed one small human triggered avalanche and one naturally triggered avalanche on the south side of Tincan ridge.  The larger of these avalanches was big enough to injure or bury a person.  While most of these wind slabs are isolated in their distribution, they can cause problems for people venturing into steep starting zones and above terrain traps such as cliffs, trees and gullies.  Wind slabs can be detected by their look and feel; snow that looks smooth and rounded or feels hollow should be avoided.

 

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 plague us.  While the likelihood of triggering an avalanche in old layers of snow at the base of the snowpack is low, the possibility remains.  It has been 12 days since a deep slab avalanche has been reported in the backcountry.  What is more important to remember is that the consequences of one of these avalanches are high for a person.  The volume of these avalanches are typically enough to cause significant damage.  We have been fortunate this season in two instances where people triggered very large avalanches in which no one was injured, buried or killed.  Continuing to treat large steep open terrain with respect will help to avoid encountering this problem today.

Weather
Fri, January 25th, 2013

The mountains around Eastern Turnagain Arm have picked up a trace of new snow overnight.   Winds have been light out of the West.   Freezing level has dropped down to sea level and ridgetop temps have averaged in the low 20s F.

Temperatures will be on the decrease through the day reaching the single digits by tonight.   Winds will be out of the West averaging 10 mph with gusts to 25 mph.   There is a slight chance of continued precip today, with accumulations of up to 1″.   Any snowfall should taper off by midday.

Expect clear and cold weather this weekend, with temps remaining in the single digits at ridgetops .   The next chance for snow around Turnagain Arm looks to be on Monday.

__________________________________________________________________________________

Kevin will issue the next advisory tomorrow morning, January 26th.

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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.