Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, November 30th, 2018 - 7:00AM
Expires
Sat, December 1st, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is MODERATE above 2500′ where triggering a slab 1-3′ thick is possible on slopes steeper than 35 degrees. Be aware of changing weather and wind slabs forming late afternoon.

At treeline (below 2500′) the avalanche danger is LOW where a strong crust has formed and capped the snowpack.

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Fri, November 30th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
No Rating (0)
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

In the alpine a thicker snowpack exists and with it more uncertainty.  Observers yesterday found depths to be in the 3-5’ range near 3000’. Two pit locations above 3000’ (on Tincan & Sunburst) found a layer of surface hoar buried 2-3’ below the surface. One party on Sunburst felt a collapse ‘whumpf’ around 2800’ along the West ridge and several large piles of debris were noted on steep Northern terrain from avalanches earlier in the week.

What does this all mean?

Triggering a large persistent slab is possible in steep terrain and will be more likely in thinner areas of the snowpack. It remains unknown how widespread this layer is across our region or how much avalanche activity occurred on it early in the storm that may be hidden. It may be more likely to trigger a persistent slab in places that received less overall precipitation like the Southern end of Turnagain Pass and Summit Lake. Persistent weak layers are tricky and hard to manage. Evaluate your consequences and choose conservative terrain. Be on the lookout for any obvious signs on instability like whumpfing, shooting cracks or any new avalanche activity.

 

Several snowpits dug in the upper elevations yesterday found buried surface hoar

 

Rollerballs and a small mid storm avalanche were visible yesterday. This visual is a little deceiving. Loose snow is covering a thin crust, but gradually disappears around 2700′. 

 

A strong crust has formed below 2500’ but the snowpack remains very thin to nonexistent below 1500′.

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Easterly winds are expected to increase to Moderate (15-25mph) late afternoon and into the evening. In the alpine there is snow available for transport and triggering a shallow wind slab on leeward features may be possible. Pay close attention to changing weather and be on the lookout for shooting cracks and drifting snow.

Weather
Fri, November 30th, 2018

Yesterday: Temperatures remained below freezing with ridgetops near 15F most of the day and mid 20F’s near 1000′. Winds were light and variable. No measureable amount of precipitation fell.   Skies were broken in the morning becoming overcast in the afternoon.

Today: Winds are expected to be light and variable in the morning shifting to an Easterly pattern and increasing to Moderate (15-30mph) by tonight. Temperatures are expected to remain below freezing in the mid and upper elevations for today. Scattered snow showers are possible in the upper elevations and skies will be overcast.    

Tomorrow:  Saturday temperatures are expected to rise as a second front moves up Cook Inlet. Rain/snowline may push as high as 1500′ by late morning. A few inches of snow is possible above this elevation and rain showers at lower elevations. Easterly ridgetop winds will remain Moderate (15-25mph) through Saturday evening.  

*Seattle Ridge weather station stopped collecting wind data at 10 pm on Nov 27, 2018.  *Center Ridge weather station depth sensor showed 2″ increase, but no actual accumulation occurred.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0 0   *10
Summit Lake (1400′) 19   0   0   0  
Alyeska Mid (1700′) 25   0   0    *N/A

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 15   Variable   1   11  
Seattle Ridge (2400′) 21   *N/A   *N/A   *N/A  
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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