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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 7th, 2013 - 7:00AM
Expires
Tue, January 8th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is CONSIDERABLE above and below treeline today, where new snow and winds continue to add stress to a potentially volatile snowpack.   Human triggered avalanches are likely in steep wind loaded terrain.   Natural avalanches are still possible.   Conservative route finding will be critical in avoiding avalanches today.

Special Announcements

From AKDOT:

There will be intermittent closures for avalanche hazard reduction work today between Bird and Portage, milepost 99-82.   Motorists should expect delays of up to 45 minutes between 10am and 2pm.

Updates will be posted on the 511 system at:

http://511.alaska.gov/

Mon, January 7th, 2013
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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
  • 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

Deep Slabs continue to be our biggest threat.  With snowfall amounts moderating over the past several days, the undetectable nature of this problem has increased.  However, moderate loading in the past 24 hours coupled with more precip forecasted for today, should increase the chances of pulling out one of these deadly slides.  Large natural avalanches are still possible today, as we have seen a continuation of natural avalanche activity over the past several days.  The challenge now is that many areas might be able to support the weight of potentially an entire group of skiers or snowmachiners.  All it takes is finding the wrong spot (thinner parts of a slab) to create serious problems.  Avoiding likely trigger points, slopes over 35 degrees, and big open terrain is the best way to tiptoe around this dangerous and persistent problem.

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

While 10″ of new snow is enough of a load to be a concern, the bonding of new storm snow to the surface has been good of late.  Look for fresh new wind slabs to be reactive to the weight of a person or snowmachine today.  While these slabs don’t carry the same consequences as a deep slab, they warrant attention, as they can entrain enough snow on their own to injure or bury a person.  These wind slabs also have some potential, once released, to pull out deeper weak layers.  Look for this problem to be more prevalent above treeline today.

Weather
Mon, January 7th, 2013

In the past 24 hours Turnagain Pass has picked up 10″ of new snow with 1″ of water.   Ridegtop winds have averaged 25 mph out of the East with gusts to 52.   Temps at 3800 feet have averaged in the low 20s with freezing levels hovering between sea level and the 500 foot elevation.

A slow moving low pressure system over us today will produce up to 8″ of new snow, winds out of the East at 20-40 mph and temps at 1000′ around 30 degrees F.

The pattern of unsettled weather should continue later in the week, with a break in the action tomorrow and Wednesday.  

_______________________________________________________________________________________________

Wendy will issue the next advisory tomorrow morning, January 8th.

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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.