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Wed, March 29th, 2017 - 7:00AM
Thu, March 30th, 2017 - 7:00AM
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is HIGH  on all aspects and elevations today. 1-2′ of new snow sits on weak snow. Both natural and human triggered loose snow and slab avalanches are likely.  More snow fell in Portage, Placer and Girdwood Valley than on Turnagain Pass, avalanches will be larger in those areas.  Travel in avalanche terrain is not recommended.

Keep in mind  the additional springtime possibility of the sun shining during a pocket of afternoon clearing and natural avalanches on Southerly slopes.  

Hiking in Portage Valley:  Travel past the end of the designated Byron Glacier trail in not recommended due to exposure to avalanche terrain. Natural avalanches are likely today.

Summit Lake: Read the  Saturday Summit Summary  HERE.

Wed, March 29th, 2017
Above 2,500'
4 - High
Avalanche risk
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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
  • 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

An active weather pattern has finally returned to Southcentral. Yesterday saw periods of heavy snow, rain showers up to 1100′ and gusty winds along ridge tops. There was also an afternoon spike in temperature bringing the warmest we have seen this spring. Snow continues to fall this morning bumping storm totals to over foot across the region and up to 2′ in Girdwood Valley, Portage and most likely Placer. Spring storms can bring somewhat complicated avalanche conditions to mountains due to the variety of issues. Today due to active loading and the chance of clearing in the afternoon with direct sunshine we recommend avoiding travel in avalanche terrain. Avalanches may run into the flats below. Avoid runout zones. 

STORM/WIND SLABS: Snow surface prior to this storm consisted of surface hoar with loose faceted snow underneath on shaded aspects, and a sun crust on solar aspects (SW – SE). Both of these surfaces will be hard for the new snow to stick to. Storm related slabs are likely and are expected to be easy to initiate. Easterly ridgetop winds yesterday will have also made slabs more cohesive on leeward slopes. These could be hard to distinguish due to new snow on top. 

DRY LOOSE SNOW AVALANCHES (SLUFFS): Both natural and human triggered dry loose snow avalanches on steeper terrain are likely especially on slopes with slick sun crusts and features protected from any wind. 

WET LOOSE AVALANCHES: If snow turns to rain wet loose activity will be likely at low elevations. In addition, if there is afternoon clearing and the sun pokes out warming the snow surface, wet loose avalanche activity on Southerly slopes will also be likely.

Tincan yesterday. Photo: Andy Moderow

Petes South at 6:00 pm. Recent loose snow avalanches on the south face after a period of clearing. 


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

Over the weekend there were two human triggered avalanches. On Saturday there was a snowboard triggered slide in Warm-up Bowl on a slope with previous tracks on it. On Sunday there was a small slab avalanche on a steep Northern chute on Orca, near Girdwood. These are good reminder that some slopes harboring old slabs 1-2′ thick are sitting on weak faceted snow. These slabs are composed of last week’s storm snow. There is a chance that avalanches occurring today could step down to weak layers deeper in the snowpack, another reason to avoid avalanche terrain today. 



Warm-up Bowl snowboard triggered avalanche. Photo: Craig Brokensha

Wed, March 29th, 2017

Yesterday was an active weather day with periods of heavy snow, rain showers below approximately 1100′, pockets of clearing, gusty SE winds and rapidly warming mid-day temperatures. Accumulations ranged from around 6″ at Turnagain Pass to over a foot in Girdwood, Portage and Placer. Temperatures spiked in the late afternoon with Center Ridge hitting 39F around 1 pm. Precipitation turned from rain to snow at lower elevations for a few hours. SE Winds were 10-20 mph and gusted into the 30s.  

Overnight temperatures dropped into the 20s and snowfall picked up early this morning adding to the snow totals. Snow is expected to continue today with an additional 3-11″ forecasted. Winds will be light and easterly. Temperatures will be in the 20Fs to low 30Fs. There will be a break in systems this evening with the next storm moving in tomorrow afternoon. This next storm is forecasted to be stronger and warmer.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   6 .4   69
Summit Lake (1400′) 29 7 .4 36
Alyeska Mid (1700′) 30 13 .9 72

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21    ENE  12 37  
Seattle Ridge (2400′) 24  SE  12 30  
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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.