Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Heavy snowfall and strong winds are in the forecast as a big storm heads our way. Stormy conditions, difficult travel, and increasing avalanche danger are reasons to enough to stick with a simple plan on Sunday. Stay on lower-angled slopes with less exposure to bigger, avalanche-prone terrain overhead

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2.5

    Between heavy snowfall, strong winds, snowpack variability, and conditions that make travel and assessment difficult, it’s not the day to try to thread the needle. New and wind-drifted snow will add a significant load to weaker layers in the upper snowpack. This includes crust-facet combinations and also some areas where surface hoar was capped, preserved, and buried by a few inches of new snow on Saturday. Very strong winds will create big differences in new snow depth, with some slopes heavily scoured and others piled high with slab. Changes in temperature and snowfall intensity can also create instability within the layers of new snow.

    Stormy conditions should develop throughout the day. In addition to avalanche danger, it might just be difficult to navigate backcountry terrain.

    Photo: Matt Lubar

Avalanche Discussion

You could see wet snow, rollerballs and wet avalanches at low and mid elevations on Sunday, especially if temperatures and snow levels are slightly higher than forecast. Stay off and away from steep slopes where you find any of the above.

The most noteworthy observations going into the weekend have to do with snowpack structure. While the facets above the Early February Crust (EFC) were found to be quite rounded and resistant to propagation in many areas, in others, they are still well-defined and produce propagation in testing. 

Surface hoar is also a wild card. The sun beat it down on solar aspects and got blown off exposed terrain. Warm snow on Saturday beat it up even more. Still, one observer was able to trigger a small avalanche that released in a layer of buried surface hoar on Saturday in the Baker BC. NWAC Forecasters in Snoqualmie Pass observed surface hoar getting buried and preserved by new snow as well. Other layer interfaces in the upper snowpack also continued to show easy results with tilt tests, etc.

The conclusion is that actual danger will vary from slope to slope due to differences in snowpack structure, wind scouring and loading, and sun exposure. We may see a wide range of avalanche activity - from nothing to big natural avalanches with no discernable pattern - with heavy snowfall and wind loading in the next 36 hours.. 

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