Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, January 17th, 2019 - 7:00AM
Expires
Fri, January 18th, 2019 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  MODERATE  above 2,500′. Wind slabs 1-2′ thick will be possible to trigger on wind-loaded terrain features on all aspects. In addition, glide cracks may release into avalanches; limit/avoid exposure under them. Give cornices a wide berth.

SUMMIT LAKE / JOHNSON PASS:  Keep in mind buried weak layers exist in the middle and base of the snowpack. More potential for triggering a large slab avalanche exists in this zone, especially in terrain that was recently wind-loaded.  

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Thu, January 17th, 2019
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
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
Low (1)
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
  • 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 and cornices are the primary concern today above 2500′ due to recent strong winds and warm temps. Varying amounts of precipitation have fallen across the region this week, 4-6” in Turnagain Pass and 8-10” in Girdwood. Easterly winds (20-50mph) redistributed this snow by scouring ridges and loading slopes in the Alpine. These pillow-shaped wind slabs are visible on all aspects including cross-loading on windward aspects and top-loading on leeward aspects. Let’s not forget what this new snow may be resting on! Last week’s cold snap created very weak surface snow (surface hoar and near surface facets.) Wind slabs may be 1-2′ thick and sitting on isolated pockets of weak snow or connected across a slope.

Evaluating surface conditions will be key if venturing into the backcountry. A surface crust has formed in the mid and lower elevations due to rain the last few days and a slight cooling trend today. Once into the alpine look for loading patterns and feel for firm snow over softer snow. Be weary of hard supportable snow especially if it feels hollow or drum-like. Shooting cracks and whumpfing may not be present until a slab releases suddenly. Wind slabs could be stiff enough to allow a person onto them before releasing. 

Cornices:  Recent strong winds and new snow have added stress to cornices. Not only can they break farther back than expected, they may be more tender than usual. Give these features lots of space.

Strong winds have transported snow in the alpine. This is a photo of the North side of Magnum where many gullies are cross-loaded.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

South of Turnagain – Johnson Pass/Summit Lake zone: A poor snowpack structure exists in these areas and strong winds over the last few days have loaded leeward slopes. Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as concerning facet/crust combinations in the bottom of the snowpack. If you’re headed this way, evaluate terrain exposure and the snowpack as you travel. Be on the lookout for signs of instability and be suspicious of any wind-loaded slopes.

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

Many glide cracks are covered with recent snow/wind and may be hard to spot. Remember the known areas with cracks are Eddies, Tincan, Sunburst, Magnum, Cornbiscuit, Lipps, Seattle Ridge, Johnson Pass, Lynx Creek, Summit Lake, Petersen Creek, and Girdwood. Avoiding/limiting time under these features is prudent as they can release into an avalanche at any time and are completely unpredictable.

Weather
Thu, January 17th, 2019

Yesterday: Strong Easterly winds diminished to light in the morning. Skies were overcast and light rain fell most of the day, but only a trace was recorded. Temperatures remained above freezing in the mid and lower elevations and rain/snow line may have reached 3000’+ in coastal areas of our zone. Partial clearing occurred overnight.

Today: This morning temperatures are expected to fall into the mid 20’s F in the Alpine as skies will continue to clear. Temperatures at sea level should dip below freezing by this evening. Wind will be light and variable. No precipitation is expected today.  

Tomorrow: Clear skies should continue through Friday. Temperatures will remain in the 20’s F and winds are expected to remain light. The next chance for precipitation is Saturday into Sunday.  

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0   .1   52  
Summit Lake (1400′) 33   0 0   21  
Alyeska Mid (1700′) 35   0    .02 40  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   ENE   9   37  
Seattle Ridge (2400′) 32   *N/A   *N/A     *N/A    
Observations
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Date Region Location
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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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