Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

More sun and warmth means there may be an uptick in wet avalanche activity on Wednesday. If the snow is wet, or you see rollerballs or small slides on steep, sunny slopes then avoid those slopes and the terrain beneath them. You may still be able to trigger an avalanche in wind drifted snow at upper elevations. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    You may still be able to find a wind slab that could avalanche with a human trigger at upper elevations on Wednesday. If you do trigger a wind slab, there's a good chance that it will be in a high consequence area, like if you're in a gully, around rock features, or in a cliffy area with a steep, unsupported slope. An avalanche could also be triggered on the leeward side of a ridge, where wind deposits snow. Taking a ride in any of these areas wouldn't be ideal. You might get buried deep in a gully or at an abrupt bench, or sent off a cliff.

    We aren't sure how reactive any of these wind slabs still are at higher elevations. Most drifts will likely be 6 inches to a foot deep, but they could be 2 or more feet deep, as was the case with the human triggered avalanche in the Stoneman Couloir in the Baker backcountry (OBSERVATION) on Sunday. At this point, there's probably a pretty low likelihood that you'll find and trigger an avalanche on a wind slab, but if you do it could be bad, due to the terrain you're in. Be sure to stop and reevaluate when you're shifting aspects, elevations, and especially if you're going to enter high consequence terrain. 

    Scan the snow surface for wind-effect: search for smooth pillows or textured surfaces as indicators that the wind affected these areas. Feel and assess for heavier or stiffer snow beneath you. Dig down to the old snow layer near the most recent crust, which could be 6 inches or a couple feet and check the bond. Does the surface layer easily pop off, or does everything stay glued together? If you have any doubt, avoid traveling in terrain steeper than 35°.

    Example photo: Avalanches on the slopes of Mt Shuksan from wind earlier in the week. These are similar to what you might be able to trigger on Wednesday- in areas where the wind desposits snow like around cliff bands and in gullies. Oftentimes high consequence terrain! Photo: Robert Hahn

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Wet loose avalanche activity will increase as the day continues. Avalanches may start on more easterly slopes in the morning before shifting south midday, and then towards the west in the afternoon. We expect an overnight freeze Tuesday night, so lower elevations and slopes that have already been impacted by the sun will start out with a crust on them. Expect these crusts to soften as the sun and warm temperatures impacts them. 

    Over the last few days we've seen a mix of sun and clouds, and increasingly warmer temperatures. Some wet avalanches have already happened. There isn't much light, fluffy snow still sitting on steep slopes facing the sun. For this reason, we aren't sure exactly how much wet avalanche activity we'll see on Wednesday. 

    It's up to you to evaluate snow and avalanche conditions and determine how to manage your terrain. If the snow becomes wet and heavy, or if you are already seeing rollerballs or small avalanches, these are obvious signs to avoid similar steep slopes or traveling in the terrain beneath those steep slopes. Stick to lower angle terrain away from steep sunny slopes, or move to shadier aspects. Areas that may not have produced avalanches in the morning when you first traveled by them may be producing avalanches later in the day. Plan your trip so you don't get caught out by wet avalanches upon your return. 

    (3/21/2021)

    Wet loose avalanches often initiate where snow sheds off rocks and trees onto the slope below. Note that there are both small rollerballs and wet loose avalanches in this image. 

    Photo: Zack McGill - Cascade Mtn Ascents

Avalanche Discussion

Many human triggered and natural avalanches were reported over the weekend. The stars aligns with beautiful weather, a healthy coating of new snow, and peoples' days off. Since then we haven't heard about people triggering avalanches, but there also haven't been many people out. We suspect that any storm and wind instabilities have strengthened, as most of the snow fell Friday night but it wasn't until Sunday that most people were stepping out and testing steep terrain. 

Most avalanches were reported in the Baker backcountry and north, towards the Canadian Border. Only one avalanche was reported on the south side of Baker, despite, several sledders out testing steep slopes. We suspect most avalanches failed in the new snow layer or beneath wind slabs, but there's a chance that avalanches may have failed on a crust, or where there may be weak layers buried in the top couple feet of snow. Depending on where you are in the zone, danger could differ and it might be easier or harder to trigger an avalanche. 

Snow surfaces vary highly. A firm melt freeze crust exists at lower elevations and steep, sunny slopes, but will likely soften as the day progresses. Wind stripped and textured, firmer surfaces appear in many other areas. Sheltered mid or upper terrain may still harbor some soft snow, maybe. If you make it into the backcountry to enjoy this warm sunny day, whether out for a walk, snowshoe, ski, or snowmobile, please share with us what you saw by submitting an observation HERE or on the App. 

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