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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 1st, 2014 - 7:00AM
Expires
Sun, March 2nd, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Conditions are variable today.  An overnight freeze-up affected lower elevations, but not ridgetops.  Areas this morning with a hard surface crust will start with a  LOW  avalanche danger today.  As the daytime temperatures melt that crust away the danger may rise to  MODERATE  for wet loose avalanche conditions.  

Upper elevations will start at  MODERATE  this morning.  Temperatures at elevations over 3000 feet have been in the mid 30s all night.  Wet loose avalanches are also the major problem for this zone.  

 Overall the avalanche concern is minor.  Large avalanches are unlikely.  Small avalanches may be manageable depending on terrain.  The weather factors to keep in mind today are rising temperatures and sun exposure that may increase the problem as the afternoon progresses.

Special Announcements

Due to warm temperatures, rain, and a decreasing snowpack all motorized areas in the Seward District and 20 mile are now closed.  The only areas open for snowmachine riding are Turnagain Pass, Johnson Pass north, Placer and Skookum.

Sat, March 1st, 2014
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. 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
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

We have seen quite a few small wet loose avalanches over the last few days.  They seem to be initiating in the top 5-6 inches of the snowpack where the water saturated snow is concentrated.  Check out this observation for a recent dye test of water percolation.

The worst case scenario with these avalanches would be stepping down into deeper layers and breaking out in a larger slab – a scenario we haven’t seen with any consistency yet.

Wet avalanches will be more likely on sun exposed southern faces this afternoon.  While we expect most avalanches of this type to be small and slow moving, terrain considerations are still important.  Channeled terrain and terrain traps should be avoided.  Trees and cliffs could make even small avalanches dangerous.  

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

The lack of overnight freeze up high is actively destabilizing cornices.  These structures are always considered unstable, but as the snow temperature increases, their strength decreases.  Today is a good day to give cornices an extra wide berth and stay out from underneath them.

Additional Concern
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

The old persistent weak layer at the January crust interface is still present.  Any activity on this layer would be an outlier, but should be considered in steep terrain, especially at high elevations >4000′.  We simply don’t have a lot of information on this problem since the most recent warmup began.  

This persistent weak layer has been responsible for many avalanches as recently as last weekend.  

Weather
Sat, March 1st, 2014

The last precipitation – in the form of rain – passed through on Thursday.  This rain had a lot more effect on the Southern Kenai peninsula near Seward than Turnagain Arm.  

Partly sunny skies are expected today with patchy morning fog.  Temperatures this morning are in the 20s at sea level, but into the mid 30s at ridgetops.  It will get warmer through the day, especially in direct sun exposure.  Wind is light and variable.  

The weather pattern looks consistent through the weekend.  Cold at night, warm during the day.  The next chance of snow looks like Monday night and Tuesday.    

Observations
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05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs
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04/23/24 Turnagain Observation: Turnagain Sunny Side
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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.