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Sat, April 1st, 2017 - 7:00AM
Sun, April 2nd, 2017 - 7:00AM
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains HIGH due snowfall, rain and strong winds  at all elevations in Turnagain Pass,  Portage, Placer and Girdwood Valley where natural avalanches 2-4′ thick are likely today.  Travel is not recommended in avalanche terrain where natural avalanches are likely occurring and human triggered avalanches are very likely.  Steer clear of gullies and the bottom of large and steep slopes in the event an avalanche releases above you.

Hiking in Portage Valley:  Travel along, and past, the designated Byron Glacier trail is not recommended due to exposure to avalanche terrain. Natural avalanches are possible today that could send debris to valley floors.

Summit Lake:  Travel in avalanche terrain is not recommended.  Read the  Saturday Summit Summary  HERE.

Special Announcements

Skookum Valley is closed to motorized use as of today,  Saturday,  April 1st.  This is an annual closure as per the Chugach National Forest Plan document.  All other motorized areas remain open – see area status on the bottom of this page for more information.  

Sat, April 1st, 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. 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

The warm, wet, windy storm continues to impact the advisory area and the message remains the same today. We don’t want to sound like a broken record but these conditions deserve respect. Slabs will likely release naturally in steep terrain and could step down into older layers in some locations. Natural avalanches could run the full length of a slope and it will be extra important to avoid being near any runout zones today. Human triggered avalanches are very likely. Snowmachiners riding near the toe of the Skookum glacier witnessed a large natural avalanche in the afternoon yesterday on a S-SW aspect. Recent natural avalanches were observed along Seattle Ridge and observers reported a lower elevation natural avalanche occurring in the afternoon in Girdwood Valley as temperatures rose. Yesterday winds blew from the SE-ENE 20-30 mph with gusts into the 50s. Winds are forecasted to be similar today, adding to wind slabs and cornices.  Large collapses (whumpfs) were observed near treeline yesterday and very reactive snow was found in snow pits at the same elevation. Snowpack tests were showing instability on the surface hoar buried by this storm cycle and the weak facets that formed during the dry spell (most of March).

How much load is on top of the weak snow (near surface facets, buried surface hoar)? Totals from 3/27-4/1.

Water weight totals measured at mid elevation stations (always more at upper elevations), snow totals verified in the field.  

Turnagain Pass:     1.8″ of H2O, 20+” of snow at upper elevations
Girdwood Valley:    2.6″ of H2O,  30+” of snow at upper elevations
Summit Lake:        .8″ of H2O,   10-12″ of snow at upper elevations

Another .65 H2O is forecasted today. More load on an already touchy snowpack! Avoidance of avalanche terrain is the only way to “manage” the avalanche hazard today. 

Natural slab avalanches on Seattle Ridge observed yesterday.

Extended column test failing on isolation at 2250′ on Tincan. Large whumpfs observed in same area. 

Facets that formed during the March high pressure were the the weak layer failing in the snowpack tests. 

Avalanche Problem 2
  • 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

Rain fell up to around 1800′ yesterday, mid elevation temperatures stayed above freezing for 24 hours and more rain is forecasted today. The rain/snow line is forecasted to remain around 1800′.  Roller balls and wet loose activity were observed at lower elevations yesterday. The snow surface is becoming more saturated as rain falls. Over a half an inch of water forecasted to fall today. This combined with temperatures in the 40Fs will keep wet loose activity likely and combo of wet/dry slab avalanches possible due to water interacting with dry snow, buried crusts and weak layers. Any sun making it through the clouds will add more heat to surface snow and promote melting. In channeled terrain an avalanche from above will likely entrain wet/damp snow in the lower elevations increasing overall volume. Again it will be important to avoid steep terrain and maintain a conservative distance from all runout zones. 

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

Don’t forget that our snowpack harbors several old layers of weak snow (near surface facets and surface hoar). Avalanches releasing in the storm snow have the potential to ‘step down’ into these layers. As the load increases as the new snow piles up and begins to stick to the old snow surface, avalanches breaking into the older, deeper layers is possible. Both of these situations can create a much larger avalanche – something to keep in mind as the storm cycle continues this weekend. Snowpack tests yesterday showed propagation potential in old layers. The question is how much incremental loading will tip the balance?

Snow pit yesterday at 1550′ on a NW aspect showing multiple old weak layers (both buried surface hoar and near surface facets) that are still reactive. 


Sat, April 1st, 2017

Yesterday was cloudy and the ceiling lifted on and off throughout the day. There were rain and snow showers with a few additional inches of snow accumulating at higher elevations. Winds continued from the ENE-SE blowing 20-30 mph gusting into the 50s. Rain/snowline fluctuated around 1800′. Temperatures rose to above 40F at low and mid elevations. Ridgetops saw mid to high 20Fs. Overnight temperatures stayed above freezing at mid elevations.

Today is forecasted to be almost identical with a little heavier precipitation.  Tonight will cool down slightly and winds will diminish. Tomorrow there is hope for those who still want winter in the NWS discussion, “As the upper low moves inland on Sunday, southwesterly cold  air advection will help to drag snow levels back down towards sea  level.”  The pattern remains active into the week.  Stay tuned!  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37   rain    .2 74  
Summit Lake (1400′) 36   rain   .1   31  
Alyeska Mid (1700′)  32  5  .7 80

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  24  ENE  27 55  
Seattle Ridge (2400′)  27 SE* 28*   48*  

*Seattle Ridge rimed up after 1 pm yesterday. No wind data after that time.

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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.