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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 22nd, 2015 - 7:00AM
Expires
Fri, January 23rd, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Today the avalanche danger is MODERATE  in the alpine. Human triggered wind slabs 4-10 € are possible today and into the early evening above 2500′.  

The avalanche danger below 2500′ will remain LOW, but look out for rocks, ice, and dirt which will be extra difficult to see as new snow covers these early season hazards below 1500′.

*It’s also important to note several additional concerns- pay attention to ridgelines with large cornice features and avoid slopes with glide cracks (2000-3000′.)  

Special Announcements

Mark you calendars for January 23rd when the APU Outdoor Studies Department and Alaska Avalanche School present  Winter Wildlands Alliance’s Backcountry Film Festival!! A night of entertainment, raffle prizes and a chance to rekindle our winter stoke is on tap. This is an AAS and F-CNFAIC fundraiser – a great way to support local avalanche education and information. Hope to see you there!

Do you ski or snowmachine in Hatcher Pass?   The Hatcher Pass Avalanche Center (HPAC) and the Alaska Avalanche School (AAS) are leading an Observer’s Workshop for backcountry enthusiasts who are interested in submitting snow and avalanche observations to the HPAC.  More info can be found by clicking here.

Thu, January 22nd, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

Today we are expecting 2-4″ of new snow above 1000’, with an addtional 3-6″ arriving later today and into this evening. This morning ridgetop winds have picked up to 15-25mph from the East and are expected to remain moderate throughout the day. This could be just enough wind and new snow to form tender wind slabs (4-10”) in upper elevations above 2500′.

These wind slabs could be easily triggered on steep features (>35°) like convexities, along gullies, or just below a steep ridgeline. Pay attention to leeward slopes that are loading and make a note of how much snow is falling throughout the day.

Over the last few days’ cold temperatures have been weakening the surface snow by creating near surface facets. 2-6″ of poorly bonded snow crystals are sitting on top of a firm bed surface (a dense wind slab at elevations above 3000’ and a melt/freeze crust at lower elevations.) This set up is less than ideal as we go into a storm cycle – depending on how the storm arrives this could be our next weak layer to track in the coming days. 

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

Many cornices have formed along ridgelines in the alpine throughout Turnagain Pass and Girdwood. These large unsupported snow formations are difficult to see sometimes or until you’re too close for comfort. Be aware of areas that have well formed cornices and give them extra space if you plan to travel along a ridgeline.  

Additional Concern
  • 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

We have been continuing to monitor glide activity over the last week, with the most recent glide avalanche occurring several days ago on the South Face of Eddies. Glide cracks are unpredictable and it can be challenging to understand the exact nature of what triggers a glide to release. It is best to avoid traveling under or on slopes with large crevasse looking cracks. 

Weather
Thu, January 22nd, 2015

Yesterday skies were clear, winds were light, 5-10mph, shifting from the East to the West throughout the day.  Valley fog kept temperatures in the single digits (6-10F) at lower elevations with ridgetops reaching low 20’s F.

As of early this morning ridgetop winds have picked up to 15-25mph from the East and temperatures have also started to increase at upper elevations (low 20’sF.) No new precipitation was recorded in the last 24 hours.

Today 2-4 € inches of snow is expected this afternoon with an additional 3-6 € into the evening. Ridgetop winds are expected to remain moderate (15-20mph) throughout the day with temperatures steadily increasing to 30F.

More snow, up to 6 € is forecasted for Friday. Temperatures should remain in the upper 20’sF to low 30’sF and ridgetop winds are expected to be light to moderate.  

*Seattle Ridge wind speed data was unavailable until 4am this morning. The below average/gust/dir are from 4am – 6am today.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 16   0   0   30  
Summit Lake (1400′) 9   0   0   6  
Alyeska Mid (1700′) 15   0    0 19  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   Var   7   27  
Seattle Ridge (2400′) 15   *ENE   *16   *34  
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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.