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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, March 14th, 2013 - 7:00AM
Expires
Fri, March 15th, 2013 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

The avalanche danger will start out low and trend toward MODERATE at all elevations as increased snowfall and easterly winds move through the Turnagain Pass area today.   Fresh wind slabs, small storm snow avalanches and potential cornice fall will all be possible today, though should prove manageable with good terrain choices.

Thu, March 14th, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

In the last 48 hours we have seen some big lines skied between Girdwood and Turnagain Pass; it’ll be a good idea to approach big terrain with extra caution today until you can answer the question: How well is todays new storm snow and fresh wind slabs bonding with yesterdays snow surface?  Forecasters found the gamut of surface conditions yesterday from impenetrable crusts at lower elevations to stiff wind board and soft wind textured powder growing surface hoar and facets at upper elevations.  Lots of quick hasty snowpits (hand pits or pole pits) to look at the storm interface may give you good information today before committing to a specific slope. 

Wind slabs forming yesterday and today are expected to be shallow in the 6-18” range proving manageable in most terrain, however pockets still exist where deeper, large avalanches are possible in isolated areas (see photo below).  As always, escape routes and zones of safety are critical when recreating in these mountains.

 

6-8’ hard slab likely ran on a buried crust sometime between March 8th and March 11th. Debris was 10-15’ deep at the toe of this avalanche.  This is a good example of a large, unmanageable avalanche that can be found in isolated areas. Notice how low on the slope the crown face is; likely due to 100+ mph winds last Thursday loading this slope well below the ridgeline.

Avalanche Problem 2
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornice fall is still very much on our radar and will be a genuine concern again today.  The good news with cornices is that they are generally easy to manage.  The fact that we can see them means we can avoid them, and avoidance is key.  Don’t spend excessive time underneath cornices and stay much further back than you think necessary when travelling along a corniced ridge.  Cornice fall is quite unpredictable, but expect them to become more unstable late in the day as temperatures and any direct sunlight warm the snow surface.

If you haven’t read Wendy’s write up on the large cornice fall and subsequent avalanche in the Goldpan area, take a few minutes and check it out here.

Weather
Thu, March 14th, 2013

Three days in a row of sunshine and blue sky in the backcountry produced a lot of smiles in the parking lots for those of us lucky enough to find a day off mid-week. Today we can expect moderate winds from the east in the 20-35mph range and mostly obscured skies as a weak surface low moves through our area.   Snow is expected throughout the day in the eastern Turnagain Arm region with totals in the 4-8 € range.   Temperatures look to stay cool enough that snow is expected at sea level.

We may squeeze another inch or two of snow out tonight as this low dissipates and skies begin clearing again overnight and into tomorrow.


Fitz will issue the next advisory Friday morning, March 15th.

Observations
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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.