Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, December 25th, 2018 - 7:00AM
Expires
Wed, December 26th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

There is a  MODERATE  avalanche danger for slopes above 1,000′.   Triggering a cornice fall or  a wind slab avalanche  will be possible in areas exposed to Saturday’s winds. Glide cracks are opening and releasing, avoid travel under them. Pay attention to weather and changing conditions. If snow amounts are higher than forecast expect the danger to rise. Watch for signs of instability.  

JOHNSON PASS / LYNX DRAINAGE / SUMMIT LAKE:    South of Turnagain Pass weak layers exists under 2-3′ of snow. Human triggered slab avalanches over 2′ thick are possible on slopes over 35 degrees. We are currently gathering information from these areas. Please consider  submitting an observation  if you head there – thank you!

LOST LAKE:    This zone is out of the advisory area, but is also suspect for harboring weak layers 2-3′ below the snow surface due to recent reports. Triggering large slab avalanche should be on the radar here as well. Pay attention for signs of instability like collapsing and recent avalanches.  

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Tue, December 25th, 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
  • Cornice
    Cornice
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

Yesterday we received a report of another cornice fall in Warm-up Bowl possibly triggered by someone walking on the ridge. Sunday night we received multiple reports of cornice falls being triggered that day.  Remember to give cornices a wide berth on the ridge as they can break off further back than expected and potentially take you for a nasty ride. They could also trigger a wind slab or larger avalanche below, creating an even bigger problem. It is also important to limit exposure time below them especially with so many people out enjoying the snow this holiday week. There is snow in the forecast today and increasing winds. This will decrease visibility and make it harder to determine where you are in relation to the cornices. 

If snow amounts are higher than forecast watch for storm slabs forming today. There is weak snow on the surface and the new snow may not bond well to the old. 

WIND SLABS:  Winds are forecast to increase today. Any new snow falling may easily get blown into start zones and begin to form tender wind slabs. In addition, Saturday’s sustained NE winds that were strong enough to move snow around and form cornices also potentially created wind slabs on steep, unsupported slopes. Yesterday there were reports cornice falls triggering small pockets of wind slab. Continue to be on the lookout for these today. At this point the older wind slabs may be quite stubborn and could allow a person well out onto them before releasing. Watch for shooting cracks, hollow sounding snow and be especially aware of the terrain – if a wind slab or cornice does release where will you go?

Dog triggered cornice fall on December 23rd. Photo: Andy Moderow 12-24-18

 Magnum ridge cornice, 12-24-18. Photo: Andy Moderow.

 

Avalanche Problem 2
  • 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

Buried weak layers roughly 2′ below the snow surface have been found in areas south of Turnagain Pass in both the Summit Lake zone and as far south as Lost Lake.  We suspect the snowpack may be similar around Johnson Pass, Lynx drainage and Twin Peaks/Silver Tip. These weak layers are composed of facets associated with crusts and have been showing signs they could be reactive enough a person could trigger a large avalanche.  If you are headed to areas south of Turnagain, keep in mind triggering a large slab avalanche is possible. Listen and feel for whumpfing (collapsing of the snowpack) and look for avalanche activity from the storm that may have steeped down into the deeper layers. 

 

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Yesterday two recent glide avalanches were observed in the Lynx Creek drainage along with multiple opening cracks. Observers reported the glide cracks on Sunburst and in Warm-up (-1) Bowl are opening and continue to see new glide cracks throughout the advisory area. It is important to remember glide avalanches can release at any time and are not associated with human triggers. Limit travel underneath. It’s a case of not wanting to be in the wrong place at the wrong time.

 

 Recent glide avalanches in Lynx Creek,12-24-18. Photo: Andy Moderow

 Cornice fall and glide gracks on Sunburst, 12-24-18. Photo: Andy Moderow

Weather
Tue, December 25th, 2018

Yesterday:  Skies were mostly clear with some valley fog. Temperatures were in the teens and 20Fs with some valley bottoms hitting single digits. Winds were light. Clouds moved in overnight and temperatures are slowly rising.  

Today: Mostly cloudy skies with snow showers throughout the day, 1-7″ is forecast. Winds will be easterly 15-30 mph gusting into the 40s. Temperatures will be in the 20Fs to low 30Fs. Snow showers and gusty winds continue overnight.  

Tomorrow:  There is a chance of snow throughout the day with mostly cloudy skies, calm winds and temperatures in the 20Fs to low 30Fs. The overall weather pattern is forecast to be active at the end of the week into the weekend. Fingers crossed for a snowy 2019! #snowtosealevel

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24    0 0   58  
Summit Lake (1400′)  12      0 0   12    
Alyeska Mid (1700′) 25  0  0     32  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  20    NE 7    28
Seattle Ridge (2400′) 23   *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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