Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, April 6th, 2018 - 7:00AM
Expires
Sat, April 7th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger will remain at CONSIDERABLE on all aspects above 1000′. Triggering a storm slab 2 feet thick is likely on shaded aspects and will become more likely in the afternoon on Southerly aspects with daily warming. In addition, keep in mind there is still a chance for triggering a deeper avalanche 3-4+’ thick in older layers of the snowpack.  

Below 1000′ the avalanche danger is MODERATE where a superficial crust has formed. If the sun comes out today natural wet-loose avalanches are possible on Southerly aspects at all elevations.

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Fri, April 6th, 2018
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

A storm that ended yesterday morning left 1-2 feet of new snow across our region favoring Girdwood, Portage and the Northern side of Turnagain Pass. Several human triggered avalanches occurred on Tincan yesterday on the new/old snow interface. The most notable was a large avalanche in Hippy Bowl that released late in the afternoon on a Southwest aspect. As of now its unknown if this avalanche was natural or triggered remotely from 300+’ away. Earlier in the day observers found easy propagation on facets associated with an old sun crust on a similar aspects and elevation. Prior to this storm surface conditions were variable and consisted of melt/freeze crusts and patches of near surface facets. At this time we do not know how widespread this particular facet/crust combo is across any given slope or how long it will remain reactive. We do know that whumpfing, cracking and recent avalanches were all observed yesterday – and these are signs the snowpack needs more time to adjust. As this new snow settles and becomes more cohesive the size of a slab can increase a day or two following a storm. Today as temperatures increase in the afternoon the likelihood for triggering a larger slab will increase on Southerly aspects later in the day. On shaded aspects with dry loose snow, triggering a slab is likely at any time during the day on slopes steeper than 35 degrees.

An avalanche in Hippy Bowl on a SE aspect of Tincan occured early in the evening and its unknown if it was natural or remotely triggered from the ridge. Earlier in the day observers dug several pits and found some propagation potential on the new/old snow interface, but tests results varied in nearby locations. See video below and click HERE for details about stability tests in these locations. 

 

Small remote triggered avalanche on NW aspect on Tincay in an area where the snow remained dry all day. Note the large shooting cracks nearby. 

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

SPRINGTIME WARMING: Yesterday dozens of small wet loose avalanches occurred on South and Southeast aspects in the afternoon. This is very common in the spring on the first day of sun following a storm. Today a thin surface crust has formed on South aspects and it will take more energy to break down this crust. Warmer air has already started to move into the upper elevations and daytime highs could upper 40F’s near sea level. Pay attention to surface warming as daily temperatures will rise above freezing in the afternoon with possiblity of light rain showers. Thin cloud cover can trap the heat and sometimes intensify the affects of solar heating. A superficial crust has formed below 1000’ on all aspects and if this crust softens wet-loose avalanche activity is possible near rocks and in steep terrain. 

Loose snow avalanche triggered by sun and warming on SE aspect of Seattle Ridge in the afternoon yesterday. 

Other avalanche issues to keep in mind: 

Cornices: Daily warming and sunnier weather can make cornices more unstable. As always give cornices plenty of space and limit exposure underneath them.

Dry loose:  Dry loose “sluffing” was triggered on steep shaded terrain features yesterday. Today a fast moving ‘sluff’ could knock you over on larger slopes harboring loose dry 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

This new snow fell onto a snowpack with poor structure and several weak layers buried 2-4’ below the old surface. So far there were no avalanches reported on deeper layers of the snowpack. There remains some level uncertainty around the reactivity of these older weak layers from mid winter (facets and buried surface hoar.) Thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass are more suspect for this structure, as well as some Northern and Easterly slopes with a generally thinner pack. Trigger points in this situation are often in thinner areas near rocks, but it is also possible to trigger this avalanche problem from areas along ridges. 

Weather
Fri, April 6th, 2018

Yesterday a storm ended in the morning with little to no precipitation recorded after 6am. Skies became clear and sunny by mid afternoon. Strong Easterly wind decreased to 5-15mph from the East by late morning. Daytime high temperatures at sea level were in the mid 40F’s and mid 30F’s at 1800′ and remained in the low 20F’s near ridge tops. Overnight temps dropped into the mid to low 20F’s at all elevations.  

This morning skis will be clear and may range from partly cloudy to overcast in the afternoon. A few scattered rain/snow showers are possible in the afternoon, but no notable accumulation is expected. Warmer air associated with a surface low is expected to move into our region today and tomorrow. Daytime high temps at sea level may reach the mid to upper 40F’s and mid to upper 30F’s near ridge tops. Overnight temps should drop back into the mid to upper 20F’s. Winds will be light and variable.

Daytime temperatures on Saturday may be the warmest we’ve seen this year with a possibility of temps in the 50F’s at sea level. Overnight lows are still expected to dip below freezing into the mid 20F’s. Skies could range from cloudy to partly sunny both on Saturday and Sunday. Winds are expected to remain light and variable through the weekend.  

*The last strong gust occured at 7am on Sunburst near the end of the storm that ended yesterday morning.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30   0   0   83  
Summit Lake (1400′) 24   0   0   36  
Alyeska Mid (1700′) 30   0    .02 81  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   ENE   11   *42  
Seattle Ridge (2400′) 25   SE   7   25  
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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