Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 31st, 2018 - 7:00AM
Expires
Sun, April 1st, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger continues to be  MODERATE  above 1500′ in the periphery of the forecast zone, such as Girdwood Valley and South of Turnagain Pass. Triggering a hard slab avalanche 2-4 feet thick remains a possibility and may be triggered remotely.  A generally  LOW  danger exists in the core zone of Turnagain Pass where triggering this type of avalanche is trending toward unlikely.  Pay attention to afternoon warming and give cornices a wide berth.  

If daily warming and radiation break down a stout crust below 1000′ the danger could rise from LOW to MODERATE on Southerly aspects in the afternoon in this elevation band.  

If you are headed South of Turnagain Pass more snowpack info can be found in today’s  Summit snowpack and avalanche summary  

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Sat, March 31st, 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
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

It has been over two weeks since the last snowfall, 9 days since a strong wind event ended, and 8 days since the last human triggered avalanche. With little in the way of weather to contribute to avalanche danger the chances for triggering an avalanche are becoming unlikely. However if someone finds an unstable slope the size of the avalanche could be large and destructive. This scenario doesn’t fit neatly into the danger scale and we still recommend evaluating snow and terrain carefully and identifying features of concern.  Northern to Eastern aspects are the most suspect for harboring a generally thinner snowpack. This poor structure is the most pronounced in the periphery areas of Girdwood Valley and the South end of the Pass towards Johnson and Lynx Creek and Summit Lake. Terrain in the core Turnagain Pass zone is trending towards LOW danger, meaning triggering a slab avalanche is unlikely – but not out of the question. 

The slabs in questions are hard slabs 2-4′ thick. The weak layers in question were formed in January and are various layers of facets and buried surface hoar. Stability tests this week have been trending towards good stability in the heart of our forecast zone. The one exception being Girdwood where observers experienced a large collapse on Thursday near Goat Mountain. Without any notable weather changes to tip the balance we remain in a low probability, high consequence situation where multiple tracks could be present on a slope before someone finds a trigger point and the slope releases. These trigger points are often in thinner areas of the snowpack near rocks or in scoured areas along ridges. Evaluate the terrain for consequences before committing to a slope and practice safe travel habits to minimize exposure in avalanche terrain. 

Sunshine:
If the sun shines in full force today be aware of warming later in the day on Southerly slopes. Especially steep southerly slopes with rocks that will help heat up the snow around them, aiding in possible wet avalanche activity. As we gear up for a weekend of sunny skies, keep the afternoon warming on your radar! Yesterday several ice climbers reported a stout crust breaking down and becoming unsupportable by 4pm in the afternoon on Southern aspects just below Treeline near Hope Wye.

Deep Persistent Slab is challenging to fit into the danger scale when stability is increasing due to their potential size and already low probability of triggering. 

 

A natural on a NE aspect of Frenchy Mountain, near the Hope Wye, was noticed yesterday and its unknown how recently this occurred.  Although this is just outside of our core advisory zone, it is a good example of a thin NE aspect that may still harbor unstable snow on the Southern end of Turngain Pass. 

 

Yesterday several groups of students in an avalanche class found poor structure on Pete’s South, Magnum, and Eddies but did not get any notable failure in their stability tests. 

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices are large in many places. As we head into warmer, sunnier weather remember this can help de-stabilize them. As always, give cornices plenty of space and limit exposure underneath them.

Weather
Sat, March 31st, 2018

Yesterday skis were clear and sunny most of the day. Daytime high temperatures near sea level reached the upper 30F’s and overnight dropped to low 20F’s.   Ridgetop temperatures were much cooler remaining in the teens to low 20F’s. Westerly ridge top winds were 5-10mph.   No precipitation recorded.  

Today clear and sunny weather is on tap. Daytime temperatures may reach the upper 30F’s near sea level and low 30F’s near ridge tops. Overnight lows will be in the low 20F’s to teens near ridge tops. Northwest winds may range from 5-15mph. No precipitation is expected.  

Tomorrow looks similar and clear skies are expected through Monday. Daily warming could increase into mid-30’s tomorrow afternoon in the upper elevations. Nighttime low temps are expected to drop into the low 20F’s again. Northwest ridge top winds may pick up to Moderate on Monday into Tuesday.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  28 0   0   76  
Summit Lake (1400′) 24   0   0   31  
Alyeska Mid (1700′)  28 0   0   71  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16   W   5   15  
Seattle Ridge (2400′) 22   NW   4   20  
Observations
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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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