Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

We're expecting to see the sun, and loose snow avalanches will transition to moist ones on the southern half of the compass. Avoid steep slopes and the terrain beneath them when you see natural wet avalanches running down. You can trigger slab avalanches around a foot deep on steep slopes, so stick to lower-angle terrain. Deep snow immersion is a hazard to continue to take very seriously with all the new snow we just received.  

Avalanche problems

  • Loose Wet

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

    As the intense March sun shines onto steep south-facing terrain, slopes will get heavier and moisten. When this happens we expect loose snow avalanches to run on steep, sunny slopes. The avalanches may initially be mostly dry. In some circumstances, the warming may cause a stiffer, slablike formation in the surface layer so you might be able to trigger a slab of heavier snow, like this observer reported in the Snoqualmie zone on Monday. 

    As you notice the sun causing snow to get a bit heavier and if natural avalanches occur, it's time to avoid similar slopes and the runouts beneath steep slopes as well. Avalanches will probably start shallow, less than 6 inches deep, but might grow to be 1-2 or more feet deep since we have a lot of low-density new snow. Activity will shift around the compass, from easterly in the morning, around to the south and then west-facing in the afternoon. After the sun has warmed a slope expect a crust to form as it cools. 

    A lot of uncertainty exists with the energy balance for Tuesday, so there's a small chance there won't be much wet avalanche activity. On the other hand, it could really go off. The good thing about this avalanche type is that it's fairly predictable: once you start seeing any avalanche activity, avoid nearby avalanche terrain. 

    Several feet of very low-density snow has led us to include the Loose Dry avalanche problem since Saturday. It's not going away overnight, and you can still expect loose dry avalanches to run on steep slopes in shadier areas. The activity is trending towards being human-triggered rather than natural. 

    (12/31/2021)

    Example photo: Loose avalanche triggered on a steep south-facing slope on Friday due to moistening snow surfaces. The slide packed a punch for it's smaller size (D1.5).

    Photo: Matt Primomo

  • Storm Slabs

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

    On Sunday and Monday, natural, human, and explosive-triggered slab avalanches occurred in the West North zone, where we believe conditions are most similar to the West Central zone. On Monday snowfall finally slowed, and we expect stability to rapidly improve. Don't go jumping onto steep slopes yet, as it takes a while for the several feet of snow we've received to settle. 

    Avalanches will probably fail in the last few day's storm snow layers, which may be 1-2 feet or so in depth. Many avalanches surprised people by propagating far- some even hundreds of feet! The slabs were all very soft. Some may have had subtle wind-effect, but many were non wind-affected. 

    Dry loose or wet loose avalanches (natural or human triggered) may trigger a slab avalanche. Otherwise, we expect natural activity to back off and most avalanches will require a human trigger to occur. Many avalanches will probably be small, but they may be large (D2), big enough to bury you. Consider terrain traps where you travel, as even a small avalanche could bury you deeply in a gully, carry you through trees or off a cliff. 

    You may see clues before triggering an avalanche like whumphs or long shooting cracks. Any new avalanches are obvious indicators to avoid nearby steep slopes as well. You may be able to use small test slopes to see if you can trigger small avalanches. Hand pits, if instabilities are in the top foot or two of low-density snow, could be useful for identifying weaknesses. Start on small slopes, before you go to bigger ones. To avoid avalanches on Tuesday, stay of all slopes greater than 35°. 

    (3/3/2024)

    A storm slab avalanche in the neighboring West North zone on Sunday, similar to what was probably the case in this zone: The pocket propagated both directions and the debris ended up in old growth trees. "A good old fashioned terrain trap" according to the photographer. 

    Photo: Brian Barkley

Avalanche Discussion

Snowfall totals varied greatly depending on where you were in the zone on Monday. Southern areas reported 1.5 inches of water, which likely equated to over 2 feet of snow, whereas northern locations were probably closer to a foot of snow or less. This band of moisture concluded our impressive streak that's been fairly consistent with precipitation since Februrary 24. In this time, the Skookum weather station in the southern half of the zone received 11 inches of water and the snowpack went from 20 inches to 54 inches. White Chuck almost doubled, going from 74 inches to 132 inches. 

Most of the new snow has been found to be fairly "right side up" and stable, with shallower storm snow instabilities remaining the largest concern. The low density snow we've received in the last few days has settled at the rate of several inches a day on total snow stakes. This light, fluffy snow that is settling quickly is still a serious concern for deep snow immersion hazards. 

One last thing to be aware of is that beneath the deep new snow layer, there have been very large avalanches reported in neighboring zones. These were mainly during or around our High danger period last Wednesday, with intense, heavy precipitation. They likely failed on weak layers either above the Early February Crust or above the 2/24 crust, which are about 1ft apart. It's very unlikely that a human can trigger an avalanche on this layer, which is probably 6-12 feet or so beneath the surface in most areas. A huge cornice fall would be the most likely culprit for a resulting very large avalanche.  If the weak layer is anywhere, it is probably on north-facing upper elevation slopes. Nearby zones, with much shallower snowpacks, are seeing natural and human triggered avalanches on this layer. 

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