Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

Expect increasing danger with over a foot of new snow and heavy snowfall during the day. Storm slabs should become easier to trigger and could run naturally as the day progresses. Large and widely propagating avalanches could run long distances into the overnight period, so stick to slopes less than 30 degrees and keep well away from runout zones. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–3

    Storm slabs are expected to form during the day on Wednesday as the new snow stacks up. It'll be falling on a range of surfaces with an underlying theme of being weak and/or faceted. As such, the new snow isn't expected to bond well to the old surface. Once you find signs of instability like shooting cracks, steer away from steep slopes. Small test slopes can work well, but with such variable old snow surfaces, they may not be consistently reliable. The danger at upper elevations is expected to increase to High in the afternoon with stronger winds creating thicker slabs. If you observe that it's snowing hard, it's a good time to steer clear of steep slopes altogether. Besides slab avalanches, loose avalanches may run naturally during times of heavier snow.

    3-5ft thick slabs of recent storm snow are resting on crusts and weaker layers buried in late December. Several wide and deeper avalanches occurred around the 11th. This problematic structure still exists, so shallower avalanches near the surface may entrain enough snow to trigger a very large beast. These could run full path and would be impressively large avalanches. It would be wise to stay away from large runout zones once the storm really gets underway. 

    (1/11/2024)

    Small storm slab that was easily triggered by approaching a steep convex roll.

    Photo: Matt Primomo

Avalanche Discussion

Another significant snow event should give us a solid foot and a half of new snow by the end of the day Wednesday.  Snowfall rates really pick up in the middle of the day. Avalanche danger will be less in the morning, but expected to increase quickly along with the heavier snowfall. Even if the day starts mellow, heads up, very heavy snowfall and strong winds should create stormy conditions later.

In general, the recent cold temperatures have promoted faceting of snow surfaces on all aspects, sometimes these weaker grains are lying on a crust. The variety of old surfaces includes thin crusts from the sun, zipper crusts from earlier in January, old wind board or soft wind-etched snow, and faceted grains and/or surface hoar on sheltered shaded slopes.  

Region-wide there are old crust and facet weak layers that have persisted, and may become active once again with more snow. Between the 6th and the 11th, several very large and deep avalanches have been observed in the Cascades. An couple examples of these are the 6ft deep slab at SPMR with control work on the 10th, and a very large (D3) avalanche on the NE side of Jove (estimated to have occurred on the 11th). The layer responsible for these larger slides is likely the Solstice crust, which is now about 4 feet below the surface in much of the zone. Snow profiles have shown these weak layers to consist of faceted melt forms, and some snowpack tests have given sudden and propagating results. These layers have gone dormant recently, but this storm could be enough of a load to begin seeing more activity on it.  This feeds into uncertainty with travel. The best advice is to let this storm play out, and stay away from large, steep features where full-path avalanches could run. 

Further east there is a similar but shallower snowpack structure. Here, persistent slabs are trending less likely, but remain on the menu. 

Regions covered