Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

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

The sun will come out, so snow will likely become heavy on the southern half of the compass, and loose snow avalanches may result. Avoid areas where you see new avalanches coming down. Storm snow layers from the last few days could fail around a foot deep with a human trigger, so avoid steep slopes. The new snow layer is light, fluffy, and many feet thick and in itself makes for deadly snow immersion hazards. 

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 both human-triggered and natural. 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 large and destructive, 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 moistened a surface, 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 similar avalanche terrain nearby. 

    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. 

    (3/17/2023)

    Example photo: Wet loose avalanches that initiated in steep rocky terrain on Slate Mt., similar to what you might see on Tuesday. 

  • Storm Slabs

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

    On Sunday and Monday, natural, human, and explosive-triggered slab avalanches occurred. 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 (D1), 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 off all slopes greater than 35°. 

    (3/3/2024)

    A natural avalanche in the Little Alaska area, Baker backcountry. The crown was 8-12 inches deep and propagated a couple hunderd feet across. It ran close to the basin bottom. D1.5

    Photo: Brian Barkley

Avalanche Discussion

Monday's 24-hour block was remarkable, as only .6 inches of water was recorded at Heather Meadows, but it equated to 15 inches of snow. This means the snow was 4% density- rather unheard of in this part of the country, and almost on par with Bridger Bowl's 3 feet of 4% cold smoke they just received. This was the final band of moisture that came through, concluding our impressive streak that's been fairly consistent with precipitation since Februrary 24. In this time, we've received 8 inches of water. Our snow base over doubled, from 54 inches to 123 inches at Heather Meadows, and we've got way more snow the higher you go from there. In many locations in the West North zone people are probing down to the Early February crust the full length of their probe, around 300cm- almost 10 feet! 

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. Of note, is that despite the 15 inches reported on the 24 hour snow stake, the low density snow we've receive in the last few days has settled extremely quickly, and it came out to 4 inches on the total snow stake. This light, fluffy snow that is settling quickly still is 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 that failed naturally throughout the zone, and with explosive triggers near Mt Baker Ski Area. 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 in depth. 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. An avalanche 2 course in the Baker backcountry over the weekend searched for weaknesses above these crusts in very deep snow pits (3 meter plus!) and couldn't find any weak layers. If they are anywhere, they are probably on north-facing upper elevation slopes. Nearby zones, with much shallower snowpacks, are seeing natural and human triggered avalanches on this layer. 

Regions covered