Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
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Limite del bosco
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Treat all steep wind-loaded slopes as suspect at mid and upper elevations following an unusually cold and windy spring snow event.  Wind slabs have likely formed further below ridgelines than usual.  If the sun stays out, expect wet loose avalanches on very steep sunny slopes.   

Problemi valanghivi

  • Wind Slabs

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

    Strong W-NW winds continued to transport fresh snow (and graupel) on Monday.  Cold temperatures near and above treeline have likely slowed the usual post-storm healing process.  Add all of this up and wind slabs may be easier to trigger than you'd expect following a spring-time storm.  Recent wind slabs have likely formed further below ridgelines than usual following extreme winds Sunday and Sunday night.  Slabs may fail down to the 3/28 interface or within storm layers. 

    As you climb in elevation, watch for textured surfaces or smooth pillow-like piles of snow that can help you identify wind-loaded slopes to avoid.  If conditions are more sensitive than forecast, step back and choose lower angle or less wind-affected terrain.  

    Cornices are large and may be ready to fail.  Give them a wide berth as you travel along ridgelines and be aware of the overhead hazard if traveling on slopes below large cornices.  Use recent cornice development to gauge which slopes were recently loaded.   

    (3/7/2021) Textured snow surfaces like this can help you anticipate which slopes or features could harbor wind slabs. Photo: Ian Nicholson

  • Loose Wet

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

    Following fresh snowfall in spring, wet loose avalanches would usually rise to the top of our avalanche concerns. There's a fair amount of uncertainty regarding just how much sunshine we'll see over the course of the day.  There's more confidence that temperatures will remain on the cool side for late March, limiting the wet loose potential on the northerly half of the compass and higher elevations regardless of cloud cover. 

    If the sun stays out,  the potential for wet loose avalanches will quickly rise on very steep sunny slopes.  Wet loose avalanches may release naturally below steep rock faces that catch the sun.  If you see pinwheels or rollerballs,  or find yourself sinking into wet surface snow more than ankle deep,  move to lower angle or shadier terrain.   

    (3/16/2021) You'll likely see shallow wet loose avalanche activity on slopes receiving direct sunshine like the one in this photo. These avalanches become hazardous near cliffs, rocks, and confined terrain features. In isolated areas, they may become large where they entrain more surface snow.

Avalanche Discussion

A strong storm brought 6-8" at Pass level and up to 10-15" above 5000' throughout the Snoqualmie Pass zone through Monday morning.  While the snow was impressive for a spring storm, the W-NW winds were more impressive.  The Alpental top station hit 95 mph Sunday afternoon and continued to gust into the 50s on and off through Monday with cloudy skies and cold temperatures.  On Monday, a public observation from Snoqualmie Mt relayed wind-affected snow starting below treeline and evidence of poor bonding between upside down storm layers and the previous snow surface. 

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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