Avalanche forecast

Olympics

Northwest Avalanche Center
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Avalanche danger

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

Heavy snowfall and rising temperatures will rapidly build storm slabs you can trigger on steep, open slopes in the southern and eastern Olympics. Uncertainty exists regarding the potential for avalanches on shaded aspects to step down and propagate more widely on weaker interfaces in the upper snowpack. In the Hurricane Ridge area, slab avalanche concerns will be localized to wind drifts 6" or deeper.

Avalanche problems

  • Storm Slabs

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

    Generally S and SE winds will focus the majority of the incoming moisture on the southern and eastern Olympics. Once you have 8" or more of fresh snow in your terrain, the avalanche danger will ratchet up rapidly. Wind loaded slopes may reach this threshold first. Use your favorate skin track tests or inconsequential test slope to evaluate the new/old snow interface and any other interfaces you might find down to the more prominent 2/7 crust. If you find these interfaces shearing cleanly, you notice propagating cracks as you move through the terrain, or you hear settlements on layers under your feet, avoid all open slopes steeper than 35 degrees. Avalanche activity of any kind is your most critical warning sign. With an unusually weak upper snowpack going into this storm, we're concerned that once storm slabs reach a threshold for avalanche activity, they won't wait long to step down to one of several weaknesses identified prior to the storm. In such a case, they could produce a large, widely propagating avalanche that would be difficult to escape. These weaknesses are most likely to be a concern on NW-N-NE aspects, but we don't have any direct snowpack information from this portion of the range.

    If the weather forecast pans out, the northern Olympics will be very different. Lower elevations have little to no pre-existing snow and hence no avalanche concerns. At middle and upper elevations, winds will transport shallower amounts of new and pre-existing snow into shallow slabs you can trigger on specific terrain features to the lee of ridgelines. A small avalanche triggered on a NW-N-NE aspect, could surprise you if it steps down to pre-existing weaknesses, perhaps growing to size 1.5.

Avalanche Discussion

It's not very often that we may reach the threashold for large storm slab avalanches just a day after we have negligible slab concerns, but here we are. It has been a strange winter in the Olympics and across most of the western United States. Unusual circumstances and the accompanying uncertainty generally dictates a more conservative mindset if you are in an area receiving substantial incoming snowfall.

Friday was a dry, cloudy day in the Olympics with temperatures in the 10s and low 20s. With no recorded precipitation in the last 24 hours, not much has changed at Hurricane Ridge since ONP rangers traveled to West Angeles on Thursday. They found up to 8-10" of low-density snow above the 2/7 crust, with typical amounts in the 4-6" range and 3" or so on S aspects. Several potential weaknesses exist, but until there is a load on top, they found minimal potential for avalanches. Multiple potential weaknesses exist in the upper snowpack. You may find a layer of surface hoar (buried 2/16) around 2-3" below the snow surface on shaded aspects. This was replaced by a warming crust on W-S-E aspects. A second layer of weak snow formed just above the 2/7 crust from a 1/2" of snow that fell 2/9 and underwent faceting and surface hoar formation with several clear nights. This layer was buried on 2/13. This layer is also believed to have been mostly eliminated on all but NW-N-NE aspects. We'd be especially interested to hear if you encounter these weaknesses and where. ONP rangers hit bare ground multiple times while riding on Thursday. Ride carefully and slowly until we have more snow on the ground.

The weak upper snowpack structure in the northern Olympics will undoubtedly bear some similarities to that of the southern and eastern Olympics where we expect to have the weaknesses tested sooner. If you head to these areas, take the time to dig and understand the snowpack structure to determine the degree of snowpack weakness in your terrain. Keep in mind that throughout the terrain, there is a large variation in coverage, crusts, and weak layer evolution by elevation and aspect. 

 

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