Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 22nd, 2018 - 7:00AM
Expires
Fri, March 23rd, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  MODERATE  above 1000′. Triggering a large, destructive slab avalanche 2-4+ feet thick is possible on all aspects above 1000′ and may be remotely triggered. Watch for wind slabs along ridgelines and avoid cornices. Pay attention to afternoon warming. Evaluate snow and terrain carefully.  

Below 1000′ avalanche danger is LOW where a stout surface crust has formed on all aspects.

Check out the  Summit snowpack and avalanche summary  if you are headed South of Turnagain Pass.

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Thu, March 22nd, 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

A skier or snowmachiner triggering a deep slab avalanche 2-4+ feet thick remains a very real and scary possibility.  Strong Northwest winds over the last three days have been loading a variety of aspects and scouring ridge lines. This wind direction can funnel through Turnagain Pass and cause unusual loading patterns opposite of our normal Easterly storm tracks. If you’re out hunting for soft snow, be aware that dozens of large human triggered avalanches have occurred over the last 10 days across our region (Seward to Girdwood) including a large avalanche triggered remotely by a helicopter on Tuesday in Girdwood. Knowing where in the terrain a large and destructive avalanche could be triggered is a difficult question. It may be the 10th person onto the slope that finds a thin part of the snowpack (a trigger point) or it could be a person triggering a slab remotely on an adjacent slope or below. There is a lot of uncertainty around this avalanche problem due to well preserved and widespread buried surface hoar and facets under a thick, connected slab 2-4+ feet thick. This structure has been found at all elevations and on all aspects. Daily warming and radiation from the sun can make it easier to trigger in the afternoons and evenings, especially if winds are calm. 

With a deep slab problem it is important to remember no signs of instability may be present before a slope releases.  It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point.

A large avalanche was remotely triggered by a helicopter in Winner Creek near Girdwood on Tuesday. This avalanche was triggered from 1/4 of a mile away at 2500′ and released on the layer of weak faceted snow on a slick crust that has been the culprit in most of the avalanches over the past week. 

 

A natural slab avalanche on a Northeast aspect of Raggedtop Peak in Girdwood at 3800′ was first seen on Tuesday morning, but it’s unknown when this avalanche released.

 

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

Wind Slabs: Be aware of newly formed wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading from strong Northwest winds this week.  Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Look for cracking and identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. Warming from the sun can make triggering easier in the afternoon, and a wind slab could step down to older snow and create a much deeper and more dangerous avalanche.

Cornices: Cornices are large and looming and the sun and above freezing temperatures can make them more unstable. Give these an extra wide berth and limit exposure underneath them.  A cornice fall could trigger an avalanche on a slope below.

Strong NW winds moving snow around on Tincan Tuesday. 

Weather
Thu, March 22nd, 2018

Yesterday strong NW winds 20-50mph (recorded on Seattle Ridge) continued for the third day in a row throughout our region and were more pronounced in Gap zones like Turnagain Arm. Overnight NW winds decreased to 10-20mph. Temperatures in the upper elevations were in the teens F and temperatures at sea level reached the upper 30F’s in the afternoon and dropped into the low 20F’s overnight. Skies were clear and no precipitation was recorded.  

Today expect skies to remain clear and sunny.   Northwest winds 10-20mph are expected to shift to the SE (5-20mph) by the afternoon. Daytime temperatures may reach the mid 30F’s in the upper elevations and low 40F’s at sea level. Overnight temperatures will drop back into the teens and low 20F’s.  

Friday looks similar, but with calm winds and slightly warmer temperatures on tap. The next window for precipitation is Saturday afternoon and Sunday with scatter snow showers possible. Skies are expected to become overcast by Saturday afternoon with highs in the mid 30F’s and overnight lows in the low 20F’s. Easterly ridge top winds are expected to be light.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0   0   81  
Summit Lake (1400′) 22   0   0   32  
Alyeska Mid (1700′) 22   0   0   76

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13   NW   10   37  
Seattle Ridge (2400′) 19   NW   20   50  
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/10/19 Turnagain Avalanche: Tincan and Sunburst from the air
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12/01/19 Turnagain Observation: Tincan, All elevations
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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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