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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, February 2nd, 2014 - 7:00AM
Expires
Mon, February 3rd, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Above treeline – a  MODERATE danger rating continues for deep buried persistent weak layers and windslab concerns.  

Below treeline – cold temperatures continue to freeze the rain soaked layers of snow below the surface.  Strength continues to build as the crust gets thicker.  At this point the chance of causing an avalanche below treeline is  LOW.  The crust is completely supportable for people traveling on skis.    

Special Announcements
  • Coming up on Saturday, February 8th is the  Hatcher Pass Avalanche Center 2014 Fundraiser. An eventful evening with a slide show, live music, silent auction and more are on tap. Tickets are selling fast so get yours today and support avalanche information in the Hatcher Pass area!!
Sun, February 2nd, 2014
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
  • 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

We have relatively little information from the last 5 days because so few people are getting into the backcountry right now.  Conditions are challenging with a hard “chattering” crust below treeline that is a prerequisite before you gain the slightly softer zone above treeline.  

The last major high elevation deep slab that we know of was a week ago on Goat Mountain in the Girdwood valley.  Remember that this problem doesn’t stabilize quickly like a storm slab problem.  

Above treeline the snowpack is thick, with weak snow at and near the ground.  We have been able to cause failures on these layers in test pits.

Managing this low likelihood, high consquence problem can be accomplished by limiting travel in steep terrain.  If that isn’t an option, then exposing one person at a time to steep terrain will reduce risk exposure.  

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

Recent wind has been limited, so wind slabs are generally older.  Above treeline there can be found some soft snow and some wind stiffened snow.  Watch out for pockets of stiff wind slab that may fail in small avalanches.  Unstable cornices are another subcategory that fits into wind slab concerns.  

Additional Concern
  • Announcement
    Announcement

Wendy posted this summary yesterday, which gives us a good look at the recent weather.

With many days of unseasonably warm weather during January, some of us are wondering just where did we stack up in the monthly averages. There is more data to crunch so stay tuned – but we do have a few sets of interesting numbers. Below are graphs of precipitation, SWE (Snow Water Equivalent) and Temperature. 

 

                                

Weather
Sun, February 2nd, 2014

We have not had any significant precipitation for the past week.  

Current weather has a temperature inversion across the region.  Sea level temperatures are in the mid to high teens, ridge top temperatures are in the high 20s.  Valley fog has dominated Turnagain Arm for a few days, and this will likely continue today.  Wind has been light for several days now.  These conditions are building surface hoar crystals, which could become a buried weak layer the next time it snows.

The blocking high pressure pattern is expected to continue this week.  By the end of the week – computer models are showing a pattern change but the exact nature of that weather remains uncertain.

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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.