Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

A mix of dry and wet snow avalanche problems will create increasingly dangerous conditions during the day.  Avalanches may break in surprising ways at mid and upper elevations where they build over weaker older snow.  Winds will transport snow further downslope and below ridgelines than usual. Keep terrain selection simple on Tuesday as the storm plays out.  

Problemi valanghivi

  • Loose Wet

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

    We are expecting a warm-up around mid-day with a change from snow to rain at elevations near and below 4000'.  New snow that accumulates prior to the switch will be primed to fall down steep slopes with or without your help. While most loose wet avalanches should be small, be especially careful near terrain traps.  Lower elevations overlap with early-season travel hazards; it's not hard to imagine a small avalanche pushing you into an open creek or through barely covered rocks or tree stumps.  If you see the snow surface becoming moist or observe natural rollerballs, switch to lower angle slopes. 

    (2/24/2020) Rollerballs like these are a great indication that the snow surface is becoming wet and unstable. They can be the precursor to loose wet avalanches. When you see new rollerballs, steer away from similar slopes.

  • Storm Slabs

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

    New storm and wind slabs will likely develop during the day so be prepared for both types of new snow avalanche problems.  Keep tabs on the usual predictors of instability like high snowfall rates and rising temperatures while watching for shooting cracks and listening for whumpfs as you travel. Deeper slabs are likely to form on lee aspects at mid and upper elevations due to strong west winds.

    Be prepared that slab avalanches may break in surprising ways where they build over older weaker snow.  This includes potentially triggering avalanches from lower angled slopes.  Shady aspects at mid and higher elevations and colder areas further east in the Snoqualmie Pass zone are prime suspects for this setup.   Until we know more, treat all slopes steeper than 30 degrees at mid and upper elevations with more than 6" of new snow as suspect.  

Avalanche Discussion

Last week, warm temperatures followed by a rain event helped to create a stout crust (12/9) throughout the Snoqualmie zone. This thick crust is being considered our new "ground" for the time being and has accumulated close to a foot of snow on it in some locations. Other areas have far less snow on the crust, but the dynamic remains the same.  The combination of a preserved weak layer and stout crust has our attention as new snow piles up this week.  Will the tipping point for widespread avalanche activity be with Tuesday's weather system or later in the week?  The answer is always to make your own observations and don't be lulled into complacency as we transition away from a relatively quiet period avalanche-wise. 

Recent weather wreaked havoc on the snow around Snoqualmie Pass, leaving us with variable and potentially difficult travel conditions. Firm surfaces abound under the recent fresh snow. The snowpack at lower elevations eroded during the warm and wet weather and amplified early season conditions and hazards. New snow will help, but you will likely encounter numerous open creeks, downed logs, and exposed obstacles. Some of these obstacles will now be shallowly buried, so be cautious and give yourself extra time to deal with variable conditions.

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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