Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Our forecasting season is coming to a close as we peak with the hottest day of the year and dangerous wet avalanche conditions. Temperatures are unseasonably warm- or just plain hot- causing an abundance of  large wet snow avalanches throughout the region. If you're sinking several inches into snow or noticing glide cracks above where you are, get off steep slopes and away from beneath them, because there is a good chance that they will avalanche soon. 

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Wet loose avalanches easily ran on Saturday, but most of them remained in the surface layers. Temperatures peak Saturday night with a 10,500 foot freezing level (temperatures reached 60 degrees at Mt Baker Ski Area Saturday afternoon) before slightly decreasing in the coming days.  The snowpack at nearly all elevations of the forecast zone hasn't seen a surface freeze for more than 48 hours. On Sunday you might see avalanches getting even larger and more destructive, affecting deeper layers in the snowpack up to several feet thick.  The avalanches may be larger than what you normally think of when you see “wet loose avalanches” as a problem in the avalanche forecast. Most steep south facing slopes already ran, but areas that have not seen as many avalanches could be more active as they catch up, a little behind the south facing patterns.

    Conditions change very quickly and a slope that was firm an hour or two ago may hold 6 inches of wet, unstable snow now, enough to slide if steep enough. Avoid slopes greater than 30 degrees on Sunday which are loose and unconsolidated in the top 4 inches or more.  Pay attention to the sun's location in the sky and which slopes are getting wet. The progression of the sun and softening snow moves from east in the morning, around south, then west in the afternoon. These are normally the guidelines to follow for what slopes to avoid at certain times of day, but temperatures warmed so much that even north facing slopes are avalanching, as seen in the adjacent video. Avalanches will run far, so do not linger on the lower-angle slopes beneath steeper slopes. Use a large margin for error with where you travel on Sunday. 

  • Glide Cracks

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    Many glide avalanches were reported in the last 48 hours. When they occur, they take the entire snowpack down with them, which means a depth of 10-20+ feet of snow in most areas.  These avalanches are very large and unsurvivable. Right now they are not a force to be reckoned with. Give steep areas near large rock faces or smooth grassy slopes that are covered in snow a wide berth, especially if you see glide cracks on them.  Glide cracks are usually present before the avalanche occurs. Many valley bottoms far beneath the slopes of concern are not a safe place on Sunday.  One was reported on Goat Mountain's West Peak on Friday, and Saturday two additional ones were reported nearby (see adjacent photo).  These avalanches are some of the most unpredictable types, but with the increase in occurences in the last 48 hours and even higher freezing levels forecasted, they are becoming relatively predictable- we expect several to occur on Sunday.  

    (4/17/2021) Several glide avalanches in the Goat Mountain area. The leftmost one, on Goat Mountain - West, was seen on Friday, but the other two weren't reported until Saturday. Photo: Jason Speer

Avalanche Discussion

Wet loose and glide avalanches top our list of concerns, but stay alert for wet slab avalanches as there’s a chance that saturation in the upper snowpack may weaken an interface near the surface. Cornices will melt out and sag in this springlike weather, causing failures of the huge features. Limit your time on the slopes beneath them and don't stand anywhere near their edge. They could trigger large avalanches as they abruptly load the slope beneath. These are additional reasons to travel very carefully in the backcountry this weekend, as rapid prolonged warming tends to cause very difficult-to-predict and challenging conditions.  Prepare to change your plans or head home early because of quickly changing conditions, and do not expect slopes that you traveled earlier in the day to be safe a few hours later.  

This is the final full avalanche forecast product of the 2020-21 season. As our capacity thins during the warmer months, please continue to share your observations and make use of our mountain weather forecasts (daily through the end of April). From all the forecasters at NWAC, thank you for all your support that makes this product possible, and we look forward to resuming full operations in late 2021.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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