Avalanche forecast

Hatcher Pass

Hatcher Pass Avalanche Center
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Avalanche danger

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

A winter weather advisory remains in place as a warm, moist, atmospheric river continues to impact Southcentral Alaska.

The avalanche danger is CONSIDERABLE above 2500', where heavy wet snow and intense winds have created Wind Slabs in specific terrain features. It remains possible to trigger a deeper Persistent Slab avalanche at mid and upper-elevations. Below 2500' the danger is MODERATE. There, heavy snow, rain, and strong winds will have created shallow slabs and instabilities on previous low-density snow.  

Roof avalanches are possible today as warming temperatures and rain will lead to roofs shedding their snowpack. Steer clear under eaves and awnings as snow could slide and injure you below. 

Overnight, Hatcher Pass received 4'' of snow at 1'' snow water equivalent. Another 8-12'' of snow and .5 to 1" of SWE are expected today before temperatures drop, snow dries up, winds diminish, and skies break this evening.

Dangerous avalanche conditions exist. Natural avalanches are possible and human-triggered avalanches are likely. If you're heading out today, wear your gore-tex or rain gear. Cautious route finding and conservative decision-making will help keep you out of trouble. 

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Avalanche problems

  • Wind Slabs

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

    Overnight, 4'' of new snow at 1'' SWE fell at upper elevations. Below about 2500', numbers are about halfed. Strong to intense winds continue to transport snow at mid and upper elevations, building slabs and new drifts 12-18'' deep on terrain features lee to the southeast. Today, another 8-12'' of snow at .5-1'' SWE is expected. While winds continue to blow this morning, snow, winds, and temperatures should all diminish throughout the day. As you climb in elevation or into wind-drifted terrain, avalanches will become larger and easier to trigger.

    • At low elevations and in sheltered terrain, there will be less snow, and it will be less reactive, but in steep terrain such as gully sidewalls, you could still trigger a small slab in the new snow.
    • As you climb in elevation into more wind-exposed terrain, stiffer, more sensitive slabs are likely. These areas are where you might trigger an avalanche that could injure or bury a skier or rider—especially on slopes with gullies, concavities, or cliffs.
    • We're batting 5 out of 5 for red flags, with recent snowfall, wind loading, rapid warming, recent avalanches, and cracking and collapsing within the new all being observed in the last 24hrs. This is an easy indication that means instabilities exist and avalanches are more likely.

    Look for signs of wind transport such as blowing snow, freshly formed cornices or smooth pillows, lenses or drifts of snow. Pole tests and hand pits are good indicators of slabs. Collapsing ("whumphing") or shooting cracks are indicators of unstable snowpack structure. 

    Shooting cracks were easy to make in areas where intense winds on Wednesday 14 blew snow from S/SW. 

    Photo: Hatcher Pass Avalanche Center

  • Persistent Slabs

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

    Heavy wet snow will be doing its part to test old, weak snow buried near the ground. An additional 1'' of water weight was added overnight, dropping a kettlebell on the foot of incremental loading we've seen over the last week or so. Uncertainty remains about how the snowpack will react to this additional weight, but it remains possible that avalanches could fail on weak snow near the ground, creating large, destructive avalanches. 

    Triggering a deeper avalanche up to 3' feet deep remains possible. 

    • Avalanches will be more likely on slopes steeper than about 30 degrees. 
    • Natural avalanches or small slides triggered in the new snow could step down into old buried weak layers, increasing avalanche size and consequence. 
    • Whumphing and collapsing of the snowpack are indications that there is weak snow failing near the ground. 
    • You may be able to trigger slides in gullies, alpine bowls, or on convex rolls where December's wind formed smooth, firm slabs over weak snow below.

    Today is a great day to let this problem lie and avoid steep slopes. By this evening, snowfall will be wrapping up, skies will part, and temperatures will drop dramatically. This post storm cooling trend will rapidly increase stablity in the wet snow, help create right-side-up conditions, and we'll have a much better idea if this problem is still a consideration. 

    Large facets at the bottom of our snowpack. With incremental loading, it is not certain that avalanches will be easy to trigger today, but we continue to have an "upside down" structure over loose, angular snow. 

    Photo: Hatcher Pass Avalanche Center

Avalanche Discussion

A winter weather advisory remains in place as a warm, moist, atmospheric river continues to impact Southcentral Alaska.

At the time of publishing, Hatcher Pass has received about 15'' of snow at 2.5'' SWE in the last four days. This atmospheric river will be the true test of buried weak layers in our snowpack, but even more so, it is a welcome base of heavy wet snow we desperately need.

While the same event is bringing more snow and significant avalanche danger to areas to our south, HP's thin snowpack and the comparatively smaller amount of moisture we're receiving mean instabilities are shallower, and avalanches will be smaller. This is not to say HP's conditions are not dangerous, but that we just do not yet have the snowpack to create very large avalanches. 

While this storm will create instabilities and test buried weak layers, it will also help improve coverage throughout the forecast area. As the storm makes its exit and temperatures drop, we should see a dramatic improvement in stability and travel conditions. While it's looking like we'll finish the month with clear skies, this setup could finally produce some good conditions for skiing and riding at the pass. 

Recent Avalanches:

Forecasters in the field on Wednesday observed several small, natural soft slab avalanches (D1) from the last storm cycle. It has been a week since the last human-triggered persistent slab avalanche. See Thursday 1/8 Microdot avalanche and Pro Observer observation here. 

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