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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, March 11th, 2013 - 7:00AM
Expires
Tue, March 12th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is generally LOW in many areas today.   Exceptions are on and below steep upper elevation South/Southwesterly aspects where the threat of cornice fall and loose snow avalanches will increase the hazard to MODERATE as the day warms.

Mon, March 11th, 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
  • 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

While the likelihood of triggering a cornice today will vary from slope to slope, the consequences of being near or under a cornice as it releases will be high.  Cornices have grown very large over the last several series of storms.  We have seen what can happen when one of these backcountry bombs impacts a slope.  We also received a report of a large cornice fall over the weekend in the Goldpan area that pulled out snow to the ground (stay tuned for more info on this avalanche).  Most cornices in the Turnagain Pass area are found on South and Southwest aspects.  Pay attention to what’s above you when traveling up valleys and what is below you while moving along ridgecrests.  Try to imagine what would happen if one of these beasts broke below your feet or sled or came hurtling down towards you and adjust where and how you travel accordingly.  The tricky part about potential cornice release is that it is hard to predict when they will release.  The chances of them releasing will get better as the sun hits those South and Southwest aspects. Planning your day by moving off of sunlit aspects as the surface becomes damp will allow you to minimize your expsoure to cornice falls as well as loose snow avalanches today.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

As the day heats up on sunlit aspects, expect loose snow avalanches to become easier to trigger.  Combine these relatively small avalanches with isolated pockets of wind slabs and volume will increase to the point where snow could easily knock you over.  Getting knocked over above terrain features such as cliffbands, gullies and trees will make these avalanches harder to walk away from unscathed.  Loose snow sluffs will be dry on shaded northerly aspects and be more damp on southerly aspects.  As such expect sluffs to be moving faster on shaded aspects and have potentially higher volume on sunny slopes.

 

Additional Concern

Wind Slab
Yesterday my partner and I encountered fresh shallow wind slabs above treeline in the Girdwood Valley.  Average depth of new wind slabs are less than a foot where they exist.  Many areas did not recieve enough wind to create wind slabs.  However, there was enough variation in wind patterns over the weekend that isolated pockets exist.  Also be on the lookout for older pockets of wind slab that were created with the high winds of last week.  These will be less likely to trigger but are still out there, particularly in steep upper elevation starting zones.

Weather
Mon, March 11th, 2013

In the past 24 hours the mountains around Turnagain Arm have picked up a few inches of new snow.   Winds have been generally light out of the East at 10 mph with gusts to 20 mph.   Temperatures have been in the upper teens at 3,880′ with freezing level remaining around sea level.

This morning lingering snow showers should give way to clear skies by this afternoon.   Winds will average 10mph out of the North.   Temperatures at 1,000′ will be in the low 30s F.

High pressure will dominate over the next several days with clear skies and relatively mild temps.

__________________________________________________________________

Wendy will issue the next advisory tomorrow morning, March 12th.

Observations
Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
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11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 Turnagain Observation: Tincan Trees
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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.