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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 27th, 2014 - 7:00AM
Expires
Fri, February 28th, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Temperatures have continued to rise since yesterday, and rain is predicted to reach 4700 feet today.  This degree of warmup and rain on snow is always a destabilizing factor in the snowpack.  Forecasting the degree of instability or the timing of when natural avalanches may begin is very difficult.  

Confidence in the danger rating is poor, but we may see  CONSIDERABLE  avalanche danger as a direct result of the warmup and rain.  All elevations and all aspects are suspect today.  Avalanche size and depth potential is speculation until we start seeing how the snowpack reacts to this abnormally warm weather.  

Thu, February 27th, 2014
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. 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
  • 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

As the surface snow gets wetter today it adds stress to the snowpack and may decrease snowpack strength.  Wet type avalanches may occur at either low or high elevations.  They could occur naturally or be human triggered.  

Wet avalanches may be confined to the surface layers or they could step down into deeper persistent layers.  

Avalanche Problem 2
  • 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 layer of weak facets that sits just above the stout January melt/freeze crust continues to be a concern.  There have been quite a few medium size avalanches reported on this layer over the last 2 weeks.  The most recent we know of was on the 23rd.  Read up on that here.  

 Check out this observation from Eddies on Tuesday to get a sense of the layering.  

In general, the facet layer is now 2-3 feet deep.  It continues to fail with moderate force in snow pit tests, and it will propagate.  The best advice to manage this weak layer is avoiding exposure to steep terrain.

Weather
Thu, February 27th, 2014

Temperatures rose above freezing yesterday, and continue to climb today.  Rain also started yesterday along with periods of strong wind from the Southeast.

Today, some areas are already reaching into the mid 40s F.  Rain will reach the top of most peaks in our forecast zone.  Since yesterday Center Ridge weather station  has lost 3 inches of snow depth due to the warmup.

This storm system is focusing precipitation on the southeast Kenai peninsula.  Some spillover moisture is reaching into the Grandview/Spencer and Portage areas.  Turnagain Pass, Girdwood and Turnagain Arm have only gotten a small amount of rain so far and should only get a small amount today.  Look for SE wind 15-30mph through today.

When this storm system passes by Friday afternoon we can expect clearer skies and colder temperatures into the weekend.

Temperature graph from Seattle ridge weather station, ending at 6am today.

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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.