Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can trigger slab avalanches in areas of recently wind drifted snow.  Strong east winds built fresh slabs and some new snow could make for even more. Bypass steep slopes where you identify unstable slabs by traveling on lower angle, more planar terrain.

Problemi valanghivi

  • Wind Slabs

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

    Strong winds ripped across the Cascades on Tuesday. Areas that saw very high wind speeds likely have miles of wind scoured snow pockmarked with stiff, stubborn wind slabs. Wind slabs might also be found farther downslope than normal. Areas with less wind like St. Helens could have a more typical pattern of wind loading with slabs found just below ridgeline.

    A weak storm to the south will bring 3”-6” of new snow (or more?) to some parts of West South. The new snow will either form small, fresh slabs that will mix in with the day-old slabs - or just cover them up and make them a bit harder to see.

    Cornices and other clues that show the usual direction of wind loading - normally from the south and west - might not be useful to determine where fresh wind slab lurks. Instead, just look for smooth-looking drifts. Test slopes and hand shears will help gauge wind slab reactivity and depth and can help you identify areas where they are easier to trigger. 

    (3/8/2023)

    Smooth wind slab on the left and scoured snow on the right.

Avalanche Discussion

Wet loose avalanches could be a factor on Wednesday if the sun comes out with any force. Warming might even increase wind slab reactivity for a short time. Pay attention to slopes overhead if it starts to warm up.

It was a windy, cold, and cloudy day across much of West South. Strong easterly winds - gusting to the high 70's at Crystal - redistributed any loose snow available for transport. Anywhere from zero to a few inches of new snow was recorded depending on location. Some weather stations that received snow actually recorded no snowfall, probably due to strong winds affecting snow height and precipitation measurements. Whatever did fall didn’t stay in one place for long. As expected less wind was recorded around Paradise and St. Helens but it was still enough to move some snow around.

The most notable observation from the weekend was a large human triggered avalanche in the Tatoosh Range. The crown appears to be 1’-1.5’ deep with wide propagation. Without detailed information about the weak layer and bed surface it’s hard to discern the exact setup that produced this avalanche. It could be an isolated area where a thin layer of faceted snow survived and was buried during the latest storm. Warming conditions and low clouds may also have played some role in increasing reactivity. No other avalanches of this size and type were reported over the weekend.

 

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