Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 10th, 2018 - 7:00AM
Expires
Sun, February 11th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  MODERATE  above 1000′ where winds are adding stress to the snowpack. Triggering a shallow wind slab or a deeper slab 2′ thick is possible. Active wind loading, shooting cracks and €˜whumpfuing’ are obvious clues the snowpack is unstable.   Additionally in the alpine, above 3000′, the potential for triggering a deeper more dangerous avalanche exists on slopes with a shallow snowpack. The periphery areas like the Southern end of Turnagain Pass towards Summit Lake and portions of the Girdwood area are more suspect.  

Check out the Summit Lake Summary  HERE.

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Sat, February 10th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Moderate to Strong Easterly ridgetop winds have been transporting snow and adding stress to the snowpack. Overnight Sunburst weather station recorded winds in 15-30mph range and Seattle Ridge was stronger, 20-40mph. Isolated pockets of newly formed wind slab may be easy to trigger, but more concerning will be drifting snow adding stress to a persistent slab and making the snow more cohesive. Several weak layers are buried within the top 1-2’ of the snowpack, including buried surface hoar and near surface facets. With our current snowpack structure these two avalanche problems (wind slab and persistent slab) are closely related. Basically they are both strong snow over weaker snow below. Slabs may range from small to large, soft or hard, and have the potential to break above you once committed to a steep slope. Identify smooth pillowed surfaces and evaluate the consequences of the terrain before committing to a slope. 

Easterly winds yesterday loading West facing slopes of Pyramid Peak. Winds can also cross load gullies and terrain features on all aspects.

 

 

January 21 buried surface hoar sits below 1-2′ of snow and is widespread across our region. This is one of several persistent weak layers including near surface facets that may be lurking below wind drifted snow. 

 

 

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

Weak snow can still be found near the ground and within deeper layers of the snowpack, above 3,000′. Although triggering a Deep Persistent Slab is less likely, it is worth keeping in mind that poor structure does exist in places with a generally thinner snowpack. Last Saturday (Feb.3) a large human triggered avalanche occurred on the East face of Twin Peaks and failed on weak snow (buried surface hoar and facets) sitting on a hard bed surface. This was a high consequence, hard to trigger avalanche where the 9th and10th skiers on a skin track found just the right trigger spot, a very shallow part of the snowpack. Luckily no one was caught or injured in this avalanche. A conservative approach would be to avoid large steep terrain with shallow snow cover or exposed rock. Wind scouring from overnight may be creating more trigger spots in thin snow covered areas.

The Twin Peaks avalanche was triggered at the apex of the crown in a shallow spot only 20″ deep. 

Weather
Sat, February 10th, 2018

Yesterday skis were clear with high clouds rolling in later in the evening. Ridge top winds at Seattle ridge were stronger than the rest of the area, but overnight winds increased at Sunburst weather station to 15-30mph. Seattle Ridge recorded several hours overnight with winds in the 30-40’s mph range.   An inversion kept some valley bottoms in the single digits and the alpine averaged in the low 20F’s. Radiation from the sun is starting to affect daily temperatures swings. No precip was recorded.    

Expect overcast skies today and Easterly ridge top winds in the 10-35mph range. Scattered snow showers are possible, but not much accumulation is expected. Temperatures may rise to the low 30F’s at sea level and mid to high 20F’s at higher elevations.  

Snow showers are possible Sunday, with a few inches of new snow forecasted. Another storm is tracking towards Southcentral, Alaska for Monday bringing warm temperatures and a possibility of more precipitation. At this point precipitation amounts are type (rain/snow) are uncertain.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25   0   0   62  
Summit Lake (1400′) 11   0   0   20  
Alyeska Mid (1700′) 25   0   0   51  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   ENE   12   40  
Seattle Ridge (2400′) 23   SE   22   49  
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Riding Areas
Updated Mon, December 02nd, 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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