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Thu, April 27th, 2017 - 7:00AM
Fri, April 28th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is MODERATE for today, but could increase to CONSIDERABLE by early evening.  With daily warming human triggered wet avalanches will become possible on solar aspects this afternoon. Natural wet snow avalanches will also become possible later in the day. Additionally glide cracks continue to slowly creep open and can release without warning. Carefully monitor surface crusts throughout the day and be aware of steep terrain above you that may be heating up faster than you may expect.

There is a LOW avalanche danger below 1,000′ where little snow remains. The one exception is in the Portage/Placer area where there is potential for an avalanche from above to run into this zone.  

Hiking on summer trails during the springtime warm-up (including the Byron Glacier trail, Crow Pass, etc).    Extra caution is advised for trails that cross under avalanche paths and the danger will increase in the afternoon with daily warming.  

FRIDAY APRIL 28th AVALANCHE OUTLOOK:  A MODERATE avalanche danger is expected again tomorrow during the day, but could increase to CONSIDERABLE if the sun comes out. The weather forecast for tomorrow is similar, overnight temperatures may dip slightly below freezing in the alpine and sky cover may vary from scattered rain showers to periods of sun. It will be in the afternoon and evening when the possibility for natural wet avalanches on solar aspects will increase. Please see the discussion below for more details.

Special Announcements
  • This is the final week the CNFAIC will issue avalanche forecasts.  These will be today and Saturday morning. We will be closing up shop on April 30th.
  • Observations: We will continue to monitor and post observations all spring and summer – so please keep us, and the community, posted on any snow/avalanche information you may come across on your upcoming adventures!
  • We have stopped issuing our Saturday Summit Summary for the 2016/17 season. Click  HERE  for our Springtime Avalanche tips.
Thu, April 27th, 2017
Above 2,500'
2 - Moderate
Avalanche risk
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
  • 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

A slow and steady spring time shed cycle persists. This is where above freezing temperatures cause the snowpack to loose its strength and becomes wet and saturated releasing naturally or with the weight of a person/snowmachine. The last two nights we’ve seen temperatures dip below freezing again in the upper elevations – causing a crust to form. Unfortunately this re-freeze is superficial and clouds have kept some heat in and mid elevations temps are still above freezing. Today and tomorrow it will be important to monitor this crust and pay attention to how much the sun and/or rain showers break it down. This is the time of year when avalanches from above can catch you by surprise. Solar aspects in the afternoon and evening are most vulnerable. Be aware that steep rocky areas with thin snow coverage heat up fast and natural activity will be more likely in these areas – including slopes that have already seen lots of avalanche activity. For Friday: If skies remain cloudy overnight and temperatures remain above freezing in the alpine a surface crust on Northern aspects may start to melt, making wet avalanches possible on all aspects.  

Things to keep in mind if you are headed out: 

  1. Is the snowpack frozen or wet and soggy? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
  2. Are you punching through a shallow crust into wet soggy snow? A shallow re-freeze is still weak and could avalanche.
  3. Are you seeing recent avalanches?
  4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
  5. Buried weak layers in the pack can make a small avalanche or sluff larger by propagating across the slope and/or stepping down.
  6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

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

Similar to the wet issues above, glide avalanches are also occurring with the springtime melt-down. Glide cracks are opening up and releasing on many slopes in the region – steer clear of any slopes harboring glide cracks. Check out the photo below from the motorized up-track. This slope is notorious for producing glide avalanches. Additional glide avalanche activity is expected today and through the week.

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

There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6′ deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. On upper elevation North, West and Easterly aspects these weak layers could re-activate if the surface crust starts to melt and become wet on these aspects. If this melting occurrs triggering a larger natural slab avalanche may be possible.

Thu, April 27th, 2017

Yesterday skies were partly clouding with scattered rain showers. Northerly ridgetop winds were light.   Day time temperatures reached a high of 55F in the mid elevations and 40F in the upper elevations. Late in the evening widespread thin cloud cover was observed across the forecast zone. Overnight temperatures reached a low of 29F in the upper elevations and 35F in the mid elevations.  

Today scattered rain showers will persist and patches of sunny skies are possible. Only a trace of precip (0.05″) is expected today and up to 0.15″ overnight. Daily temperatures are expected to reach the mid 50Fs in the afternoon and 40F in the upper elevations.   Overnight lows are expected to remain above freezing (mid 30F’s) in the mid elevations reach just below freezing (30F) in the alpine. Winds are expected to remain light from the North.  

A very similar weather pattern is expected Friday and into the weekend. Scattered rain showers and partly cloudy skies are expected vary accross the forecast region. Easterly ridge top winds may increase Friday night into Saturday, 15-20mph.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 45   0   0   54  
Summit Lake (1400′) 41   0   0   13  
Alyeska Mid (1700′) 41   0   .03   50  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 34   NE   3   8  
Seattle Ridge (2400′) n/a   E   3   10  
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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.