Avalanche forecast

Hatcher Pass

Hatcher Pass Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 6 months ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger is MODERATE  above 2,500' for WIND SLAB and PERSISTENT SLAB avalanches. The danger is LOW  below 2,500'.

While our recent February trickle of snow has drastically improved riding conditions, new snow avalanches will still be possible to human-trigger today.

Shallow, buried wind slabs that formed mid-storm will be lingering in mid-upper elevations in steep terrain. Be on the lookout for thicker, more cohesive-feeling snow. Snowpack cracking, freshly formed dunes of wind-drifted snow, or a wind-textured snow surface are clues that you have found a wind-loaded slope. 

While less likely, you could still trigger larger, more destructive slides on slopes harboring a shallow snowpack, where buried weak layers near the ground are closer to the surface and easier for a skier or rider to trigger. 

Avalanche problems

  • Wind Slabs

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

    Southeasterly winds blew with speeds capable of transporting snow for over 12 hours during the last steady trickle of snow, peaking on 2/10 in the morning. There could still be soft, lingering wind slabs in upper-elevation terrain where winds were most active. Snow continued to fall following this period--expect surface clues of wind slabs to be disguised by non-drifted snow. 

    This problem most likely exists in mid to upper elevation terrain along the sides of steep cross-loaded gullies or convex rolls. You may not find obvious signs of wind loading if approaching a slope from a wind-scoured ridge, but that doesn't mean you couldn't find this problem mid-slope. 

    If you trigger a wind slab, it is likely to be a bit of a wind slab/dry loose combo avalanche, where soft and shallow wind slabs trigger and entrain dry loose snow on the same slopes. Pay particular attention on large faces and cross-loaded gullies directly below ridgelines today. Pole probing, hand pits, and small slope tests are all useful tools for this problem. 

    DRY LOOSE: 

    In steep terrain above 35 degrees where new snow has fallen over firm surfaces, you will be likely to trigger dry loose sluffs. While these sluffs are most likely to be small (D1-1.5), even a small unexpected sluff in a committing terrain feature could have high consequences and knock you off your feet and carry you somewhere you do not want to wind up. 

     

    This 02/12 wind slab avalanche on Marmot was an intentional ski cut and propagated down the gully wall, entraining loose snow. 

    Photo: Andy Paul

  • Persistent Slabs

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

    Despite a period of warming temperatures and a nice February trickle of snow, our snowpack structure remains poor. Even though new snow did not overload this setup (triggering natural avalanches), in shallow areas in upper elevations that harbor shallow structure, you could still trigger an avalanche where old buried interfaces harbor persistent weak layers or deeper in the snowpack in weak, sugary snow above the ground. 

    At mid elevations below 3,500', it is possible that cumulative snow and wind load has tipped the scale to make this problem more sensitive to human-triggered events. As you travel, remember your chances of finding and triggering a persistent slab avalanche up to 3' deep will be higher as you gain elevation and proximity to steep, shallow, rocky terrain.

    The easiest way to manage this problem is to select terrain with a steepness of less than about 30 degrees. If you do choose to get into avalanche terrain (slopes steeper than 30 degrees), you can pick terrain with a seemingly uniformly deep snow pack greater than about 3' deep—although be aware that you could trigger a slide from the edges or the middle of a slope where the snowpack is shallow and variable. 

    Despite a nice February trickle of snow, our snowpack structure remains poor. Even though new snow did not overload this setup (triggering natural avalanches), in areas that harbor shallow structure, you could still trigger an avalanche where old buried interfaces harbor persistent weak layers or deeper in the snowpack in weak, sugary snow above the ground. 

    Photo: Andy Paul

Avalanche Discussion

New snow soft slab reactivity and distribution was overall less than anticipated yesterday. Still, there are lots of pieces of untested terrain in the forecast area where mid-storm winds transported snow and slabs were then buried by soft, gentle snow. 

You are most likely to trigger avalanches where the wind built soft slabs during the storm. What still concerns us most are the isolated areas within the forecast zone where fresh drifts have formed over a shallow, weak snowpack. In these spots, you could trigger avalanches that fail wider and deeper than you expect.

We now have a few mid to upper snowpack layers we are tracking:

  • The new snow/old snow interface where the 2/08-2/11 storm snow fell on firm crusts or wind board. Many of these surfaces had begun faceting prior to the storm.
  • Buried wind slab/facet or crust/facet combos. These will most likely be found in the top 1-2' of the snowpack.  

Last but not least is the weak, sugary, and faceted snow near the ground. This varies in size and depth but is relatively widespread. This is a good time to remember that as stability improves, we still have an overall weak structure, and you could still trigger a persistent slab avalanche of higher consequence (see video below).

The takeaway is that today’s avalanche problems are mostly centered on new snow and wind. But if you’re committing to steep slopes, don’t rule out the possibility of triggering a larger, more destructive avalanche that fails near the ground.

Lingering persistent slab problems can be frustrating, especially as the season goes on and obvious signs of instability—like cracking and collapsing—become scarce. As we continue to get more snow and the Hatcher Pass snowpack deepens, triggering a slide that fails near the ground will become more difficult. However, we’re not there yet on all slopes. There are still plenty of areas where the snowpack remains thin, variable, and weak.

RECENT AVALANCHES: 

Forecasters in the field over the last two days observed several dry, loose avalanches in steep, craggy terrain and small wind slabs on steep, wind-loaded slopes. These were all small D1s. Yesterday, a party triggered a D1.5 soft slab avalanche at about 1500 on the W side of Marmot at 4,300' in Tomahawk Alley (between Mid Rib and the Lodge Run. It appeared to have failed where new snow met firm, old wind-affected surfaces in this location and had a crown (see photo below and all recent observations here). 

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