Avalanche forecast

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Haines Avalanche Center
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Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

The avalanche danger isCONSIDERABLE above 1,500ft and MODERATE below this. Northerly outflow winds over the past five days have transported snow-forming wind slabs on slopes greater than 30 degrees. Additional stress to buried weak layers could introduce step-down potential for larger avalanches. Use visual clues to identify snow that has been redistributed and factor in wide safety margins that reduce exposure to terrain and route choices. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    North and northwest winds with moderate to strong gusts may continue to transport snow, forming slabs on slopes greater than 30 degrees. Be on high alert near summits, along ridgelines, cross-loaded gullies, and terrain traps. Look for visual clues, including cracking and areas where winds have scoured slopes and then re-deposited onto loaded slopes.

    Winds could erode and weaken previously formed cornices and create new ones. We should give these a wide distance for safety and minimize our time near them.  Cornices are a good indicator that slopes below them have unstable snow and can be a large natural trigger for an avalanche, especially where persistent slabs (see Problem 2) are present.

    (3/2/2024)

    The winds have continued to re-distribute snow even at mid-elevations 5 days after the wind event began.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–3

    This period of cold weather will accelerate faceting on the surface and within the snowpack. Weak layers that can propagate from shallow to deeper areas include buried surface hoar, facets, melt-freeze layers, and depth hoar.  Signs of instability could be apparent, such as large whumphs and collapses, or non-existent. A trigger like a cornice fall or wind slab could release deeper instabilities. Slope-by-slope assessment is key.

    Remain suspect of unsupported slopes and shallow areas in the snowpack. Consider the consequences of large destructive avalanches along your route. Weak layers may be more or less apparent in certain areas, making mapping the problem tricky. Utilize cautious route-finding and minimize exposure by choosing safe spots to re-group and traveling one at a time. Travel where the snowpack is deep, consistent, and strong.

    (2/23/24)

    Old snow layers at Chilkat Pass 5-Mile Creek at 2,500ft SW aspect

Avalanche Discussion

Yesterday's winds kept their intensity, and a slight change in direction kicked up more snow, visually transporting it along ridgelines, peaks, and mid-elevations. The result is a complicated wind-loading pattern in terrain that hasn't been completely scoured or protected. Some overlapping wind slabs could be more likely to human triggers, and others could behave more stubbornly. Winds and cold temperatures have been blowing, sublimating, and faceting or weakening the snowpack. Thinner areas in depth could see more accelerated faceting than deeper ones; look for weak layers there. Big natural triggers such as cornice falls, or wind slabs could affect deeper layers that have remained unlikely and dormant.

This intense outflow event with sustained temperature below 10F lasted over a week. Here are some thoughts and considerations from our forecast team. As backcountry users, we should look ahead and anticipate what comes next. We know about numerous weak layers in the snowpack, including a list of melt-freeze and ice crust layers that have recently remained dormant. Extended periods of cold temperatures, as we've had, can facet above and below these crusts and make them less strong. Dig down to assess and map these layers by probing and measuring snow depths. They might be buried too deep for an extended column test but can be assessed using the propagation saw test.

 

Thinking ahead:

  • When the next loading event happens, is it slow and incremental or rapid and significant?
  • What are the temperatures, steady and moderate, spring diurnal, or are freezing levels rising?
  • How does the likelihood of propagation increase or decrease with strength vs. structure?
  • Is there weak snow above or below a crust? How strong or brittle is the crust? Does the crust laminate well to layers above/below or not?
  • Could strong solar radiation or warming temperatures contribute to instabilities, including cornice fall?

List of layers in the snowpack & approximate depths:

  • Down 0-30cm. Near-surface facets or "recycled powder" are at the surface in terrain protected from the wind.
  • Down 10-40cm. Valentine's inversion melt-freeze crust and buried surface hoar. Includes hard sun-warmed surfaces.
  • Down 40-70cm. A sneaky February 7th near surface facet layer that got buried by Feb. 10-11th snowfall and warming.
  • Down 70-160cm. The late January Pineapple Express crust. An intense precip event saw pooling and percolation warming to 5,000ft.
  • Down 150-170cm. End-of-Year Crust (EOY). Wet and warm ended at the end of last year freezing levels to 4,000ft.

Click here for a detailed season weather & snowpack history.

 

The people you go out with, how you communicate, and how you practice risk reduction as a team throughout the day are equally important as the conditions. Always practice safe travel techniques and terrain management- only exposing one person to a slope at a time, avoid grouping up in run-out zones, and re-consider islands of safety to truly limit your group's exposure. Carry radios, first-aid, and a two-way emergency communication device. Take an avalanche course, and practice companion rescue often with your riding group. Every scenario is different, so it pays to be prepared.

Help us gather information about weather, snowpack, and avalanche activity by reading and submitting field observations. Useful observations can be anonymous and include: 

  • Avalanche Activity: Natural or human-triggered
  • Signs of Instability: Cracking, collapsing, or whumping
  • Red Flag Weather: Precipitation, wind loading, warming temperatures and rain-on-snow
  • Persistent Weak Layers: Surface hoar growth, snow depth, persistent weak layers, etc
  • Snow Pits: Stability test results, layers of concern, total snow depth, location, elevation, aspect, etc 

Were you caught, carried, injured, or buried in a slide? We can benefit from anonymous lessons learned. Please report incidents to Haines Avalanche Center staff confidentially.

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