Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Use caution before jumping into more consequential terrain where you see signs of recently drifted snow.  Shallow wind slabs may lurk at upper elevations, including below ridgelines and cliffs, or in chutes.  If the sun comes out for an extended period, expect steep sunny slopes to shed new snow in the form of rollerballs or even small wet loose avalanches. 

Problemi valanghivi

  • Wind Slabs

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

    It's a rinse and repeat in this cold, not too windy, scattered snow shower pattern.  Continue to keep an eye out for recently formed wind slabs that are lingering at higher elevations and below cliff bands, in rocky chutes, or right below ridgelines. 

    Steer around steep lee slopes below ridgelines where you see recently drifted snow.  You may not see obvious clues like shooting cracks or recent avalanches before stepping into more consequential terrain. While wind slab avalanches will likely be small, they may break easier than expected above a firm crust or older weaker snow on northerly aspects. Use extra caution around terrain traps where a small avalanche could cause injury.   

    (1/5/2023)

    An example from earlier this winter of a shallow wind slab you could trigger in steep lee terrain below ridgelines at higher elevations.

    Photo: Small skier triggered wind slab on the leeward side in Liberty Bowl, next to South Early Winter Spire. SW, 7,450ft.

    Photo: NWAC Public obs

  • Loose Wet

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

    While the clouds will likely win the afternoon once again, it won't take long during morning or mid-day sunbreaks for steep sunny slopes to shed loose snow downhill in the form of rollerballs or pinwheels.  

    In areas that have received a few inches of snow over the last few days, small wet loose avalanches are possible if those sunbreaks stick around longer than expected.  Small wet loose avalanches are only likely to be an issue when combined with a terrain trap. 

    Even with a cold overnight and start to the day, it's spring-time and that means not lingering on slopes below cornices or recently formed glide cracks.  If traveling along ridgelines, make sure to stay well back of cornices, some may be sagging from last week's milder weather. 

    Rollerballs shedding below rocky features are indicators that small wet loose avalanches may not be far behind on similar slopes.  

    Photo: Robert Hahn

Avalanche Discussion

Before conditions cooled on Thursday, the recent spring weather really affected the old snow surface. A crust of variable thickness formed on E-S-W aspects high into the terrain due to sunshine and in shadier areas at lower elevations because of warm temperatures. Higher northerly aspects still managed to preserve cold dry soft snow over the past week.  While not much new snow has fallen since Thursday, be aware of refrozen chunks of rollerballs or small wet loose avalanches that may be lurking under a shallow fresh coating of new snow. 

While this storm shouldn’t be enough to wake up deeper weak layers, we are still tracking a few interfaces in the snowpack. The Valentine's crust is 3-5 feet below the surface in the western half of the zone. You can expect to find shallower at lower elevations and further east. There have been numerous observations and snowpack tests indicating weak snow and poor structure exist below this crust. It's suspected to have been a weak layer for some of the very large avalanches at the end of the last storm cycle. We have less of an understanding of the progression of these layers east of Mazama and the Twisp River drainage.

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