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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, February 7th, 2021 - 7:00AM
Expires
Mon, February 8th, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

Today’s avalanche danger is MODERATE at elevations above 1000’, where it will be possible to trigger an avalanche 1-2’ deep on steep slopes where stiff, older wind slabs sit on top of a layer of weak snow. If you are trying to access steeper terrain, be sure to avoid previously wind-loaded slopes with stiff slabs at the surface. Slopes without a stiff slab on top will be safer in general, but be aware of fast-moving sluffs gaining volume with 6-12” loose, unconsolidated snow at the surface.

The avalanche danger is LOW below 1000’.

SUMMIT LAKE: There are weak layers deeper in the snowpack that are still capable of producing avalanches in the Summit Lake area. The most recent activity on this layer was a natural wind slab avalanche that stepped down to facets near the ground last Monday (Feb. 1).

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Sun, February 7th, 2021
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)
Recent Avalanches

Seattle Ridge: One skier was caught and carried, but not buried, after triggering a small avalanche 10” deep and 40’ wide. The skier was uninjured. More details here.

Seattle Ridge: Snowmachiners were able to trigger small wind slab avalanches failing on a layer of surface hoar buried 4-16” deep. Details and photos here.

Tincan: A skier remotely triggered an avalanche in the Tincan trees, which propagated 30’ wide and 10” deep on the buried surface hoar layer, and ran for 100 vertical feet. Details here, video here.

Looking down at the debris pile from a remotely-triggered avalanche in the Tincan trees yesterday. Photo: Nick D’Alessio. 02.06.2021

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
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

The biggest concern today will be triggering an avalanche 1-2’ deep where a stiff slab rests on a weak layer of buried surface hoar and faceted snow. Thankfully, it does not look like yesterday’s winds got quite as strong as we were anticipating. Although we were spared any widespread damage, the light to moderate winds have redistributed snow into stiff slabs on some slopes, which sit on top of a weak layer of buried surface hoar and near-surface facets. We received reports of human-triggered avalanches from two different groups on Seattle Ridge (details here and here) and a third group in the Tincan Trees (details) yesterday. It is still possible to trigger an avalanche on slopes that have seen previous loading, with stiff snow at the surface today. These may be recognized from a distance by their smooth, pillowy texture, or you might notice stiffer, ‘punchy’, hollow slabs as you approach a potentially dangerous slope. This combination will sometimes– not always– show clues of instability, like shooting cracks or collapsing. If you see any of these signs of instability, choose different terrain that has not been previously wind-loaded. Sheltered terrain will have the best riding conditions anyway. With varying wind directions since our last snowfall, it is difficult to identify any kind of pattern with wind loading. Be on the lookout near ridgelines, convexities, and cross-loaded gullies on any aspect.

There are some areas for which we have limited observations from yesterday, that tend to experience stronger winds when we have these northwesterly wind events. Be extra cautious if you plan on heading out in near Crow Pass, or in the Summit Lake area, as these places may have seen stronger winds yesterday than weather stations are able to capture.

Loose Snow Avalanches (Sluffs): Continued cold and clear weather is keeping the surface snow dry and loose in areas that have been sheltered from the wind. Be aware of fast-moving and high-volume sluffs in steep terrain, especially if you are traveling near terrain traps like cliffs, rocks, trees, or gullies.

Cornices: Cracks have opened up where large cornices are peeling away from cornices. If you are traveling along ridgelines be sure to give them plenty of space, and minimize the amount of time you spend traveling below them. Cornices will fail easily under the weight of a person, and they may trigger an avalanche if they fall on a wind-loaded slope below.

Snowmachine-triggered wind slab on the north end of Seattle Ridge. Photo: Sean Fallon. 02.06.2021

 

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 have opened up throughout the area. These avalanches are unpredictable and they are large since they involve the entire season’s snowpack. Avoid spending any time on or below slopes with glide cracks, and if you see any new glide activity please let us know here.

Weather
Sun, February 7th, 2021

Yesterday: High temperatures reached the upper teens to low 20’s F under mostly sunny skies, with some lingering valley fog through the day. Northwesterly winds were blowing 5-15 mph at the ridgetops, with gusts to 31 mph at Sunburst. Low temperatures were in the single digits below zero F at Summit Lake, and in the single digits to low teens above zero F near Girdwood and Turnagain Pass.

Today: Another day of clear skies is on tap for today as an upper level high-pressure ridge stays in place over the area. Westerly winds are expected to stay around 5-15 mph, and temperatures are expected to reach the mid- to upper teens F.

Tomorrow:  Low temperatures will dip down into the single digits F tonight, and possibly below zero again near Summit Lake. Highs tomorrow are expected in the mid- to upper teens F tomorrow, with westerly winds blowing 5-10 mph. We are expecting another day of mostly sunny skies, with no precipitation.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 20 0 0 118
Summit Lake (1400′) 9 0 0 43
Alyeska Mid (1700′) 15 0 0 108

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13 W 9 31
Seattle Ridge (2400′) 18 NW 7 19
Observations
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Riding Areas
Updated Tue, June 01st, 2021

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
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.