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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, January 19th, 2019 - 7:00AM
Expires
Sun, January 20th, 2019 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is  MODERATE  above 2500′ for slab avalanches 1-2′ thick. Triggering a small slab in isolated terrain or a larger slab that could bury a person is possible on steep slopes. Cornices grew last week and could be triggered by the weight of a person or snowmachine. Identify glide cracks and avoid/limit your exposure time under this unpredictable hazard.

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 has seen recent wind-loading.  

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Sat, January 19th, 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
  • 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

Although sunny and quiet weather conditions have been over the area for 2 days, there is still the possibility of triggering a lingering slab. Winds, along with several inches of snow, on Wednesday formed slabs that are sitting on weak facets and possibly even buried surface hoar in places. This is the problem, that slabs could be taking more time to stabilize due to the persistent grain type that lies under them. Slab thickness is variable – from 3″ to a foot in general with wind loaded zones that could harbor a section of 2′ slab. Keeping close tabs on the top of the snowpack is key.

Quick hand and/or pole tests to determine stiffer snow over weaker snow as well as watching for cracking around you are ways to asses a slab over a weak layer. Keep in mind smaller and harder slabs could be lurking in steep rocky terrain as well as larger and more connected slabs in bigger terrain. Be suspect of wind-loaded features and as always, evaluate the terrain for consequences and use safe travel protocols.

 

South of Turnagain – Johnson Pass/Summit Lake zone: A very poor snowpack structure exists in these areas.  Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as a facet/crust combination in the bottom of the snowpack. No recent avalanche activity has been observed since the New Year’s storm, but more uncertainty exists for triggering a deeper more dangerous avalanche. If you’re headed this way, it will be important to evaluate terrain and snowpack as you travel. Be on the lookout for signs of instability and maintain extra caution around wind-loaded slopes. 

Surface conditions between 2,500 and 3,000′ on Magnum’s West face. Small roller balls are old, from Wednesday’s warm and windy weather. (photo: Trip Kinney)

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

Glide cracks are still slowly opening. Although we have not heard/seen one of these release for over a week now, limiting exposure under them remains wise. Known areas with cracks are Eddies, Tincan, Sunburst, Magnum, Cornbiscuit, Lipps, Seattle Ridge, Johnson Pass, Lynx Creek, Summit Lake, Petersen Creek, and Girdwood. This avalanche hazard is unpredictable and cracks can release without warning. 

Glide cracks on the SW aspect on Magnum, photographed Thursday Jan 17 by Peter Smith.

Weather
Sat, January 19th, 2019

Yesterday:   Clear skies with dense valley fog in places were seen over the region. Temperatures were inverted with teens in valley bottoms and mid-20’sF along ridgetops during the day. Winds were light and variable along ridgelines. Overnight, winds shifted to a more NW direction bringing in cooler air aloft.

Today:   Another clear sky day is on tap.  Ridgetop winds are expected to remain light from the NW.  The inversion is breaking down with the arrival of cooler air from the NW. Temperatures sit in the teens F at all elevations this morning where they are forecast to remain for the day. The exception is Summit Lake, where temperature have dropped into the single digits.  

Tomorrow:    The last day for this clear sky period is expected tomorrow. Temperatures will continue to decrease and single digits are expected. Clouds, warming temps and a chance for snow move in on Monday, while a higher chance for snowfall is forecast for Tuesday into Wednesday.  

 *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′) 23   0   0   51  
Summit Lake (1400′) 9   0   0   20  
Alyeska Mid (1700′) 21   0   0   38  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   Variable   3   9  
Seattle Ridge (2400′) 27   *N/A   *N/A     *N/A    
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/08/19 Turnagain Avalanche: Tincan
12/06/19 Turnagain Avalanche: Sunburst
12/04/19 Turnagain Observation: Sunburst
12/03/19 Turnagain Observation: Hippy Bowl
12/01/19 Turnagain Observation: Tincan, All elevations
12/01/19 Turnagain Observation: Tincan
11/30/19 Turnagain Observation: Tincan Treeline Plateau/ Common Bowl/ Ridge
11/29/19 Turnagain Observation: Sunburst Ob #2
11/29/19 Turnagain Observation: Sunburst Ob #1
11/27/19 Turnagain Observation: Tincan
Riding Areas
Updated Mon, December 02nd, 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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