Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

This week is an abrupt reminder that it's springtime in the Cascades, and the daily avalanche forecasts end today, but avalanches will not. 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. 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Wet loose avalanches were easy to trigger on Saturday, and natural avalanches were plentiful. Temperatures will peak Sunday morning, reaching 10,500 feet before finally decreasing slightly in the coming days. Avalanches have mainly been limited to surface layers, however with this final push of sustained heat, they may entrain more snow, and could become larger. These are not the normal springtime conditions, or what you may think of when you see  “wet loose avalanches” as a problem in the avalanche forecast. 

    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. 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

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Many glide avalanches were reported in the last 48 hours, including one that was witnessed Friday morning on Whitehorse. When glide avalanches occur, they take the entire snowpack down with them, which means a depth of 10-20 feet of snow in many 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.  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.  

    (4/16/2021) Large glide cracks, compressions and a glide avalanche on a north aspect at 4400ft in the northern Mountain Loop Highway area. Photo: Steve Kuznetzov

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. There was a report of a 6 inch deep wet slab avalanches in the Stevens Pass zone on a south aspect at 5500ft. 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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