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Tue, February 2nd, 2021 - 7:00AM
Wed, February 3rd, 2021 - 7:00AM
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE today above 1000’. It will be possible to trigger an avalanche on a layer of weak snow buried 1-2’ deep. While this weak layer may be found on most slopes in the area, the key factor determining stability will be whether there is a slab of stiffer snow at the surface. Avoid traveling on slopes that have seen wind loading since last Friday, and pay attention to other indicators of instability like shooting cracks, collapsing, and other avalanches.

The avalanche danger is LOW below 1000’.

PLACER/PORTAGE VALLEY/WHITTIER: These areas received 12-18″ snow during last week’s storm, and have seen stronger winds since. This will make larger avalanches possible.

SUMMIT LAKE: This area has seen more wind, and as a result it is more likely to find slopes with a cohesive slab of snow sitting on top of the buried weak layer. Observers saw natural wind slab activity yesterday near Fresno Ridge.

SEWARD/SNUG: Winds are expected to be stronger near Seward today. It will be important to pay attention to continuing loading through the day today, in addition to the persistent slab problems linked to older wind slabs from the past few days.

Special Announcements

Forecaster Chat #4: Snowmachine Specific- Head on a Swivel! Join us Tonight from 7-8:30pm, for a VIRTUAL snowmachine-specific discussion with Graham Predeger and snowmachine educator and rider Tim Thomas from Haines. Details and free registration HERE.

Tue, February 2nd, 2021
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Dangerous avalanche conditions. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Recent Avalanches

Summit Lake: Skiers reported a natural avalanche failing near the surface on a wind-loaded slope in the Colorado/Fresno area.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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

Last week’s snowfall buried a layer of surface hoar and near-surface facets that has been producing avalanches on wind-loaded slopes for the past few days. We are expecting the winds to calm down today, but unfortunately the avalanche danger will not do the same. The nature of these persistent weak layers is that they are capable of producing avalanches long after any kind of loading event. For today, the best way to stay out of trouble will be by identifying and avoiding any steep slopes with stiff snow at the surface. After several days of cold and clear weather, most slopes have 6-8” loose, unconsolidated snow at the surface unless they have seen any wind-loading since Friday. These slopes with loose snow at the surface are not capable of producing persistent slab avalanches because they are lacking a cohesive slab capable of propagating a fracture. The danger will lie on the slopes that have seen wind loading since Friday, which has built a dangerous structure with a relatively stiff slab of snow at the surface sitting on top of a layer of relatively weak snow buried 1-2′ deep.

Because we are dealing with a persistent weak layer, slopes that have seen wind loading will not gain strength as quickly as they normally would. In addition to monitoring surface conditions, be on the lookout for other key indicators of instability- shooting cracks, collapsing, and fresh avalanche activity.

Loose Snow Avalanches (Sluffs): Several days of cold and clear weather has kept 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: Large cornices are starting to peel away from ridgelines, opening up large cracks and becoming especially sensitive to human triggers. 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.

Stiff, wind-textured surface in the Crow Creek area yesterday. 02.01.2021

This surface hoar was the culprit in a skier-triggered avalanche on Eddie’s late last week, and will continue to be cause for concern today. Photo: Nick D’Alessio. 01.29.2021

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 continue to open up throughout the area. These avalanches are unpredictable and large– they involve the entire season’s snowpack. Avoid spending any time on or below slopes with glide cracks, as they can release unexpectedly. If you see any new glide activity, please let us know here.

Tue, February 2nd, 2021

Yesterday: We saw another day of clear skies and cold temperatures, with highs in the single digits to low teens F. Low temperatures were near or slightly below 0 in Girdwood and Turnagain Pass, and down to -14 F in the Summit Lake area. Light winds were blowing 5-15 mph at the ridgetops from variable directions.

Today: Cloud cover is expected to increase through the day today as the upper-level ridge moves out of our area. Temperatures will reach the mid- to upper teens F today, and drop down to the single digits to low teens tonight. Winds are expected to remain calm to light, blowing 0-10 mph out of the east at ridgetops.

Tomorrow: Skies will clear through the day tomorrow, with highs expected in the mid- to upper teens F. Winds are expected to remain light, at 0-5 mph out of the east at ridgetops. We could see a trace of snow overnight.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 2 0 0 123
Summit Lake (1400′) -6 0 0 42
Alyeska Mid (1700′) 2 0 0 109

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 4 W-NE 8 27
Seattle Ridge (2400′) 2 VAR 5 16
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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.