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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, April 2nd, 2017 - 7:00AM
Expires
Mon, April 3rd, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger remains HIGH at all elevations in the mountains and travel in avalanche terrain is not recommended. Continual rain, snow and wind are keeping the snowpack unstable. Natural slab avalanches 2-4′ thick are possible at all elevations and human triggered slab avalanches are likely. These can be large and debris may run to valley floors. If choosing to travel in the backcountry outside of avalanche terrain, make sure to be extra conservative and  steer well clear of gullies and the bottom of large and steep slopes in the event an avalanche releases above you.

*We may not see the amount of natural avalanche activity like we did yesterday, but nonetheless, it’s not a day to travel in avalanche terrain, hence the danger remains  HIGH  for the travel advice portion on the  North American Danger Scale.

Hiking in Portage Valley:  Travel along hiking trails that are exposed to avalanche terrain is not recommended. This includes the Byron Glacier trail and the Crow Pass trail. Natural avalanches are possible that could send debris over trails.

Summit Lake:    Dangerous avalanche conditions exist.  Read the  Saturday Summit Summary  HERE.

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Sun, April 2nd, 2017
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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

After a cold and dry March, April is starting us off with a wet sucker punch. Yesterday was the 5th day in a row of elevated avalanche danger due to a series of storm systems moving through. The cycle began with a system bringing snow to sea level (1-3+’ throughout the forecast zone) and this last system (Friday and Saturday) bringing rain to 1,800′. Over the last 24-hours we have picked up ~.4-.7″ of rain below 1,200′ and 4-8″ of new snow above. Today will be a short break between storms before another warm low-pressure moves in tonight – see the satellite image HERE. Although precipitation and temperatures are backing off today, the winds are not, and all of these will ramp back up tomorrow, keeping the snowpack in an unstable state. 

RECENT AVALANCHE ACTIVITY:
Significant natural wet slab avalanche activity was seen yesterday as rain fell and saturated the 1-3′ of new snow from last week. Through thick clouds, two large wet slabs were seen at Turnagain Pass, photos below. How many more exist – and just not visible – is a mystery for now. An avalanche professional in the Placer Valley yesterday noted widespread natural wet slab activity occurring in the 1,500′ elevation band. This was along the steep rollovers that line the Valley, such as near Skookum Valley, Spencer Glacier and into Grandview. Wet slabs were also seen in Portage Valley near the Whittier Tunnel entrance – again all releasing near 1,500′.

Dry snow avalanche activity has been prevalent over the last 5 days in the mid and high elevations – though again much is obscured by poor visibility. Debris piles littering the bottom of large and small avalanche paths assures us that widespread naturals have been occurring. If skies part enough today, hopefully we can get a glimpse of the start zones for some of these storm snow avalanches. 

Wet slab releasing yesterday on Pete’s South ridge, Southwest aspect ~1,800′ (estimated 12-18″ thick, 300′ wide). 

 

Another wet slab releasing yesterday between 1 and 2pm on Eddies ridge, also a Southwest aspect at 1,500′ (estimated 1-2′ thick and 300′ wide). 


WET AVALANCHES:
Natural wet slabs and wet loose sluffs below 1,800′ are possible today with human triggered slabs and sluffs likely. Once the skies clear and/or temperatures cool enough for the saturated snow in this lower elevation band to begin to freeze up – this issue will get locked into place – but until then, wet avalanches are not manageable and nothing to mess with.

Avalanche Problem 2
  • 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

Above 1,500′ where the snow is drier we can expect storm snow instabilities to persist today. These are:

WIND SLABS and CORNICES:
Non-stop Easterly winds will continue to load slopes and build cornices with the new warm, sticky snow. Ridgetop Easterly winds are expected to average 20-35 mph, perfect for keeping the pack unstable. Natural cornice falls are likely and could easily trigger a slab below them.

LOOSE SNOW AVALANCHES:
Sluffs in the dry snow are likely, but much less of an issue compared to the much larger slab avalanche and cornice fall problem.

Debris from the lower slopes of Seattle Ridge – an indication of dry snow avalanches occurring above. 

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

Several old layers of weak snow (near surface facets and surface hoar) sit buried in the snowpack. Avalanches releasing in the storm snow have the potential to ‘step down’ into them. Furthermore, as the new snow piles up and begins to stick to the old snow surface, avalanches breaking into deeper layers are also possible. Both of these situations can create a much larger avalanche – something to keep in mind as the storm cycle continues. Snowpack tests are still showing propagation potential in these layers. The question is how much incremental loading will tip the balance?

Weather
Sun, April 2nd, 2017

Yesterday’s weather consisted of obscured skies, rain to 1,200′ and light snow above. Over the past 24-hours it looks as though Turnagain Pass has picked up another 6″ of new snow above 1,500′ and the Girdwood Valley around 4-6″. Ridgetop winds have been moderate to strong from an Easterly direction, averaging 20-25mph with gusts to 50mph. Temperatures that were warm yesterday (40F up to 1,800′ in places), are on a slight cooling trend as the rain line has dropped overnight to near 500′.  

Today, the cooling trend from overnight should swing back the other way with daytime warming – temperatures are expected to be 35-40F at sea level and around 25-30F along the ridgelines. We could see the sun poke out in places but cloudy skies are most likely. Another .1-.3″ of rain may fall below 500′ with 1-3″ of new snow above this. Ridgetop winds are forecast to remain strong, averaging 20-35 mph with gusts into the 50’s from the East.

For tomorrow and early in the week, another low-pressure system is on the way. This storm looks slightly cooler than the last, rain/snow line around 500′ and bringing less moisture but keeping winds strong. Stay tuned as this active pattern continues!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36   6   0.6   77  
Summit Lake (1400′) 36   0   0   30  
Alyeska Mid (1700′) 32   3   0.42   77  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   E    21 50  
Seattle Ridge (2400′) 27   sensor rimed   sensor rimed   sensor rimed  
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Riding Areas
Updated Wed, December 11th, 2019

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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