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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 3rd, 2016 - 7:00AM
Expires
Thu, February 4th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Today the avalanche conditions will be increasing as a storm moves into our region. Right now a MODERATE danger rating still applies to the Alpine and Treeline elevations where wind slabs will be developing throughout the day. Should this storm intensify beyond the forecasted 6 €, avalanche danger may reach CONSIDERABLE by late afternoon. Be on the lookout for changing conditions and alter your plans should you see any obvious signs of instability like human or natural avalanche activity.

The avalanche danger is LOW below Treeline where the snowpack is disappearing and an avalanche from above is unlikely.

*South of Turnagian Pass harbors a different snowpack structure where a variety of weak layers persist within the snowpack. Click HERE for an observation from Fresno Ridge yesterday and HERE for the Summit Lake Summary. We also found buried surface hoar responsible for a very large avalanche on Saturday in the Groundhog Creek drainage (Johnson Pass area).   If travelling in these areas a cautious mindset and careful snowpack evaluation are essential.  

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Wed, February 3rd, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

A series of storms with a Southerly flow will be moving through Southcentral Alaska over the next few days and into the weekend. Today ridgetop winds will be in the 20-30mph with 4-6” of new snow expected to fall throughout the day. Temperatures will continue to climb, which could bring rain as high as 1200’ by this afternoon.

Wind Slabs: Expect fresh wind slabs to be tender and isolated to leeward terrain features. These slabs will be growing throughout the day and could be as thick as 12” by this afternoon. Pay attention to the wind direction and where the snow is being loaded. Shooting cracks and any observed avalanche activity is a reminder that conditions are worsening and to avoid steeper slopes.

Cornices: Cornices will continue to grow with the addition of new snow and moderate winds. These features have been tender over the last few days and may release naturally with the additional weight of blowing snow. Give cornices lots of space by avoiding travel on or below them. 

 

Moderate Northeasterly ridgetop winds were observed in Summit Lake, Fresno Ridge yesterday as well as in Turnagain Pass.

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glides continue to be widespread throughout Turnagain Pass in the 1000’-2500’ elevation band. Since glide cracks can spontaneously release at any time, take the time to identify slopes with this unpredictable hazard. This week with warming temperatures and forecasted rain and snow, glides will continue widening and may release without warning. Avoid steep slopes that harbor a big “brown frown.”

 

 

 

Glide cracks observed on the East face of Seattle Ridge from Sunburst. Photo taken on Feb.1 by Graham Predeger. 

Weather
Wed, February 3rd, 2016

Yesterday Easterly winds started building in the afternoon; 20-30mph with gusts in the 40’s mph. Temperatures also started climbing with light rain falling below 700′. Overnight 3 € of new snow was recorded at Center Ridge Weather Station.

Today moderate Easterly ridgetop winds will continue throughout the day. 4-6 € of new snow is expected, and intensity will increase by early evening. Rain may push as high as 1200′.

Overnight 1.0 € of water is forecasted which could bring another 12 € of snow above 1200′ with rain below this elevation. Moderate Easterly winds may increase to strong by early tomorrow morning. Expect stormy conditions to continue for the next few days.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   3   0.3   92  
Summit Lake (1400′) 31   trace   0.1   27  
Alyeska Mid (1700′) 32   2   0.2   69  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE   24   52  
Seattle Ridge (2400′) 25   n/a   n/a     n/a    
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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.
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