Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

The first day of spring may feel a lot like winter as a multi-day storm pattern makes its way into the West South zone. As the snow stacks up and gets drifted around by the wind, expect dangerous avalanche conditions to develop. Storm totals and avalanche potential are expected to be a notch higher on the volcanoes.

Problemi valanghivi

  • Storm Slabs

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

    We're back into stormy conditions, meaning new snow problems will again take center stage. Look for unstable slabs on slopes over 35 degrees, particularly if they're convex or wind-loaded. The volcanoes are expected to outpace the crest in terms of snowfall totals, meaning slabs could be larger and more widespread in these locations. Closer to the crest, you may find that slabs are more reactive on wind-loaded slopes. No matter how you look at it, it's shaping up to be a dangerous day in the mountains where new snow falls on a variety of surfaces and has waxing and waning reactivity. Use small test slopes, hand pits, or uptrack tests to gauge the slab potential of the new snow. If blocks of snow are failing easily in your tests, choose simpler or more treed terrain where the consequences of an avalanche could be less.

    (3/19/2025)

    A slab avalanche in a clearing in the trees. This one is deep and broke on a steep, unsupported slope. 

    Photo: Josh Lipkowitz

Avalanche Discussion

Thursday should be the start of a multi-day storm pattern that will see snowfall, wind, and slowly rising temperatures as we head toward the weekend. This first wave will favor the volcanoes for snowfall, while areas closer to the crest get more wind. Avalanche potential should be on an upward trend as the snow stacks up and those temps rise. 

This shouldn't be anything new; we've been in heightened or dangerous avalanche conditions for over a week now. Over that time, we've received several feet of new snow, resulting in multiple rounds of avalanches. While we aren't specifically calling out any particular layers in the upper snowpack as problematic, some recent interfaces may still need time to heal. The recent snow has generally been low-density, and these incoming warmer storms may result in an upside-down snowpack. Periods of clear weather have created subtle melt-freeze crusts on slopes that see direct sunshine, and convective springtime showers have resulted in graupel that can act as a weak layer. And then there's the wind. Throughout our snowy week, the wind has easily drifted the low-density snow into drifts on leeward slopes. Any old wind slabs should be on the mend, but those who haven't fully healed will be hidden beneath the fresh new snow, making them hard to assess. Add it all up, and the upper snowpack over the atmospheric river (AR) crust is variable in depth, as well as the number of subtle crusts found. Not all slopes will act the same.

These factors have been at play over the last week. Multiple parties have triggered avalanches, and a handful have been caught and carried. Since last Thursday, we have had a report of an avalanche involvement every day around the state. This includes the general public and avalanche professionals alike. Many of these groups reported being surprised, caught off guard,  or lulled into a false sense of stability. Some have said that the current avalanche landscape is "sneaky." No matter what term you use to describe the situation, note that avalanche activity and involvements have risen, and now we're heading back into a stormy pattern. 

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