Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 2 years ago.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

Highlights

Friday won’t be a typical storm day. Anticipate unstable conditions and unusual avalanche activity. Stick to low-angle, conservative terrain that limits exposure to slopes that could produce avalanches.  If you see widespread signs of instability and avalanche activity, assume High danger and avoid traveling on or below all steep slopes.

Avalanche problems

  • Storm Slabs

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

    The 1-2’ of snow forecast through Friday afternoon is not unusual. On the other hand, fresh slabs will form over a wide variety of questionable snow surfaces including slick crust, weak facets, or surface hoar - all of which developed during the last three weeks of abnormally dry conditions. 

    Don’t assume that your go-to storm terrain will offer the usual level of safety, especially if surrounded by or connected to larger and steeper slopes. The usual strategies and tricks you use to manage risk might not be so reliable given the variation in snowpack structure below the new snow. Some slopes might produce no avalanches or just the small slabs you might normally expect. Other slopes could beget unusual avalanches that propagate widely, release when you are in the middle of a slope, or might even be triggered from below.

    Stormy conditions could make it harder to evaluate stability or even see much going on in the terrain around you. It will be a good day to use some restraint and keep it low-key, especially since it hasn’t snowed in weeks and demand for powder is at an all-time high.

    You are more likely to trigger a slab avalanche on unsupported terrain like this convex roll.

    Photo: Jason Speer

Avalanche Discussion

Look for a transition to wet snow avalanche problems at low elevations. Temperatures should gradually warm through the day. Rollerballs and snow shedding from trees are signs you could start seeing wet avalanches. Small wet avalanches are signs you could see bigger ones.  Move off and away from steep slopes where you observe signs of wet avalanche instability.

The Cascades have gone through a period of dry and mostly cooler weather, the kind of weather that breeds weak snow. A week ago - during much cooler temperatures - near surface facets and surface hoar were growing large and surviving on all aspects.  A strong temperature gradient in the upper snowpack enabled faceting around and between a variety of crusts from the surface to 6-12" down to the crust buried on Jan 10th. But one of the key traits of this mountain range is things just don't stay the same for very long.  Very warm temperatures, periods of strong wind, and plenty of sun did their best to degrade weak snow at the surface and put a lid on faceting below it. 

The take-home point is we do have the setup to have a much weaker snowpack than normal. But the reality is the amount of faceting and surface hoar below the new snow is going to vary widely across a forecast zone that is literally the size of a small state on the East Coast.  While some areas won't have much in the way of weak snow, others are flush with it. The best you can do is be conservative while the storm plays out, submit observations of what you see - or don't see - and let the pattern of avalanche activity become established over the weekend before stepping into bigger terrain.

 

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