Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, December 3rd, 2018 - 7:00AM
Expires
Tue, December 4th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  above 2500′ in the Alpine. Human triggered slab avalanches up to 1-3′ thick remain possible due to a weak layer of snow under the Thanksgiving weekend storm snow. Additionally, watch for lingering wind slabs in steep wind-loaded terrain.

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Mon, December 3rd, 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, sitting anywhere from 1 to 3′ below the snow surface, is a thin layer of weak snow (buried surface hoar/BSH). An observer yesterday found this layer to still be reactive in a snowpit on Sunburst right around 2500′. This buried weak layer remains a concern. At this point obvious signs of instability may not be observed but the possibility of triggering an avalanche cannot be ruled out. As always use safe travel protocol and choose terrain with consequences in mind i.e. where is the avalanche path and where would I end up if the slope slides? The snowpack profile below illustrates the slab sitting over the weak layer.

 

         

 Snowpit on Sunburst, December 2, 2018. Observer: Chris Robertson 

  Snow cover looking south on Turnagain Pass, December 2, 2018. Photo: Allen Dahl

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

Be on the lookout for wind slabs in steep unsupported terrain. Strong easterly winds on Saturday afternoon may have loaded leeward slopes in the Alpine. It may still be possible to trigger a lingering pocket that could be dangerous. Look for stiff, pillowed snow and cracking and listen for hollow, drum-like sounds. 

Weather
Mon, December 3rd, 2018

Yesterday:  Skies were overcast and there were very light rain/snow showers. Temperatures were in the mid 30Fs to mid 20Fs. Winds were easterly 10-20 mph with gusts into the 30s.  

Today:  Cloudy skies in the morning becoming partly sunny. Temperatures will be cooling from the 30Fs into the lower 20Fs as skies clear and colder air moves over the region. Winds will be northeasterly 5-15 mph with gusts into the 20s. Expect overnight temperatures in the low 20Fs and high teens. Clouds will move back in overnight.  

Tomorrow:  Chance of snow showers and increased easterly winds in the afternoon as the next front moves over the area. The pattern remains active through the week. As usual the temperatures and timing are uncertain. Stay tuned!

*Seattle Ridge wind sensor is rimed over.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   1 0.1 13  
Summit Lake (1400′)  29     3 0.3 2
Alyeska Mid (1700′)   33     0 0.19   N/A

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24  NE  11 32  
Seattle Ridge (2400′)  29    *no data *no data   *no data  
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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