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Issued
Sun, January 31st, 2021 - 7:00AM
Expires
Mon, February 1st, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger will be MODERATE above 1000’, where it will be possible to trigger a wind slab avalanche up to a foot deep. Light winds have been able to drift the 8-10” of low-density snow at the surface into sensitive slabs on top of fragile weak layers that formed earlier in the week. These sensitive wind slabs exist on some, but not all, slopes. Today it will be important to recognize and avoid wind-loaded terrain.

The avalanche danger will be LOW below 1000’, where less soft snow at the surface and a virtual lack of wind will make avalanches unlikely.

PLACER/PORTAGE VALLEY/WHITTIER: This area received 12-18″ snow with the most recent storm, and has seen more wind in the past few days. This will make larger avalanches possible, and extra caution is advised.

LOST LAKE/SNUG/SEWARD: These areas also received more snow than the Turnagain/Girdwood/Summit areas. With 20-30 mph winds expected today, avalanche conditions may be more dangerous here than in our core advisory area. Cautious route finding will be essential in these zones.

 

Special Announcements

Forecaster Chat #4: Snowmachine Specific- Head on a Swivel! Join us Tuesday, February 2nd 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.

Sun, January 31st, 2021
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
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. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. 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

We received multiple reports of skier and snowboarder-triggered storm and wind slab avalanches yesterday. Most of these were not big enough to bury a person, but they did grab our attention. Nobody was caught or carried in any of these avalanches.

  • Lynx Creek/ Captain’s Chair: A group changed their objective after triggering multiple soft slab avalanches on their approach to Captain’s Chair.
  • Tincan: Skiers triggered multiple small slab avalanches on convex rollovers on a SW aspect. They both appear to be in slightly wind-loaded pockets.
  • Eddies: A snowboarder triggered a small soft slab on the upper west face of Eddies.
  • Seattle Ridge: Skiers triggered multiple small wind slabs in the Seattle Ridge back bowls, and a snowmachine triggered a small wind slab on the front side.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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
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

In the past two days, we have gotten reports of several human-triggered avalanches failing on the interface between the most recent storm snow and a weak layer of buried surface hoar and near-surface facets. Most, if not all, of these avalanches have occurred on slopes that had seen recent wind loading. Similar activity will be the main concern for today. We are not expecting to see any extraordinary winds during the day, but it will not take much to move the low-density snow on the surface into sensitive slabs. If your travel plans for the day involve any kind of steep terrain, it will be important to pay attention to changing conditions at the snow surface. Even a subtle increase in surface hardness could be enough to make a dangerous combination of a slab on top of very weak snow. Be on the lookout for red flags indicating increasing instability, such as shooting cracks and fresh avalanche activity. The most likely places to find unstable snow today will be near ridgelines, below convexities, or on cross-loaded slopes. With winds forecast out of the west, we might see slabs forming in unusual places today.

Sluffs: The low-density snow at the surface has been producing sluffs in steep terrain. These avalanches are not big enough to bury a person, but they could have serious consequences if they carry you into terrain traps like cliffs, trees, or rocks. If you plan on heading into steep terrain, be aware of these dry loose avalanches, and of exposure to consequential terrain below.

Cornices: We have recently seen large cornices peeling away from ridgelines, opening up large cracks (there are some good photos here). Be sure to give them plenty of space, and minimize the amount of time you spend below them.

Small skier-triggered avalanches on the SW aspect of Tincan yesterday. Photo: Adam Rothman. 01.30.2021

Cornices are starting to peel away from ridgelines, opening up large cracks. These cracks can sometimes be difficult to identify when they get bridged with blowing snow. Bertha Creek Headwall. Photo: Tony Naciuk. 01.30.2021 

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

We have been seeing more glide cracks open up recently. Glide avalanches are large and destructive, and their timing is impossible to predict. Avoid traveling on or below slopes with glide cracks, and let us know if you see any new ones open up.

Weather
Sun, January 31st, 2021

Yesterday: Winds were calm to light, blowing 0-10 mph at ridgetops. High temperatures were in the upper teens to low 20’s F, with lows in the single digits to low teens F overnight. We saw plenty of sunshine and no precipitation under clear skies.

Today: Similar weather continues today, as an upper-level ridge of high pressure stays in the area. We expect to see temperatures reach the low to mid teens F, with light winds 5-10 mph out of the northwest. We should see another sunny day, with no precipitation expected.

Tomorrow: Lows will drop down into the single digits tonight, and stay around 10 F tomorrow. Light westerly winds will continue, with another day of clear skies expected. No precipitation is expected tomorrow.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) N/A* N/A N/A N/A
Summit Lake (1400′) N/A N/A N/A N/A
Alyeska Mid (1700′) 16 0 0 109

*Snotel sites are not reporting as of 6:45 a.m.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12 W 6 13
Seattle Ridge (2400′) 13 NE 3 8
Observations
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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.
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