Bollettino valanghe

East 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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In sintesi

Another day, another few inches of snow. It is getting more difficult to trigger avalanches. But you could still get unlucky and find stiff, wind-drifted snow over a weak layer where you could trigger an avalanche. To reduce your chances of triggering a large, surprising avalanche, steer around steep slopes where you find deep, wind-textured snow.

Problemi valanghivi

  • Wind Slabs

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

    In some areas, stiff wind slabs formed over weak snow layers that take longer to strengthen, and you could still trigger a large, hard slab avalanche. These are becoming less likely with time, warmer daily temperatures, and cool nights. But a few inches of fresh snow and another bump in Southerly winds overnight maintain a possibility of triggering a wind slab. Winds have blown in multiple directions over the last few days, so look for wind slabs on various aspects or even mid-slope. Strong winds have pressed these slabs into firmer 1F-P hard slabs in exposed alpine terrain. Consider the high consequences of triggering a wind slab that breaks wider and deeper than expected if it fails on weak snow above the Early February Crust. 

    Use visual clues such as drifts around rocks or vegetation and textured surfaces to help you identify likely spots for wind slabs. Be suspect of terrain features, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. Dial it back if you notice shooting cracks, whumphs, or hollow-sounding snow. 

    (2/18/2024)

    Triggering a wind slab in the wrong spot could result in a much larger and wider avalanche if it breaks on old snow above the Early February Crust. 

    Forecasters observed this 1-2 day-old avalanche in the Teanaway drainage on Sunday. 

    W aspect, 6200 ft

    Photo: Katie Warren

Avalanche Discussion

Another day of very familiar weather is in store for Wednesday, and we'll wring out a few more inches of snow. These meager storms are slowly loading weak snow layers. This is particularly concerning in wind-drifted terrain, where slabs are much thicker and more dangerous. In many sheltered locations, there isn't enough slab structure to the snow for an avalanche. But the slab is getting deeper and more cohesive with continued precipitation and warmer temperatures. Anywhere you find more than 8 inches of snow above a stout crust or see wind-textured surfaces could be problematic. These slabs may not be that deep but could be large enough to ruin your day if they propagate widely on well-developed facets over a crust. You can use quick hand pits to observe the bond with underlying crusts. Avalanches are more likely if the snow slides easily as a cohesive block.

Lower elevations and southerly aspects have seen warming and sunshine. Both now have melt-freeze crusts of varying thickness on the surface. However, temperatures will notch up again on Wednesday, and you could see some wet loose avalanches or rollerballs a bit higher in the terrain than on Tuesday. 

Since February 14th, storms have brought 14-16 inches of snow to the East South zone. In much of the region, this new snow now sits over persistent weak layers of faceted snow over the slick Early February Crust (EFC). Observers in many areas of the Cascades, including in an NWAC forecaster in the Darland Mt area on Thursday, are finding this weak, faceted snow just above the stout EFC crust and also over a thin, breakable crust buried on 2/14 on southerly aspects. This persistent weak layer has already produced avalanches in neighboring zones (observation here). We have quite a lot of uncertainty with the sensitivity and distribution of this avalanche problem. But, since February 15th, 13 unintentionally human-triggered avalanches have failed on or just above the EFC throughout the Washington Cascades. We have reports of avalanches on all aspects between 5000ft and 8000ft. Thankfully, no one was injured in these incidents, but this is critical information that this weak layer can still produce avalanches. It is best to stick to sheltered terrain or low-angle, well-supported slopes while the weather keeps giving us windy conditions along with dribs and drabs of snow. 

Expect very thin (or even non-existent) snowpacks at lower elevations and on some steep southerly slopes. Unfortunately, we're still talking about travel hazards. Slick crusts, exposed obstacles, open creeks, and bare ground continue to make travel more adventurous. While the continued snow is a welcome refresh, it's best to use established roads and groomed trails for better access to the high country. 

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

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