Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Saturday starts with another nice window for spring skiing and riding on southerly-facing terrain. Increasing clouds today, should help keep wet avalanche concerns limited. You can keep track of developing wet avalanche problems by monitoring the snow surface as it melts. If you find a few inches of wet snow in steep terrain, small wet loose avalanches will be possible. Or, if you find conditions where your boots sink deeply into wet snow, you've found an isolated area that could potentially produce a wet slab avalanche. 

On the north half of the compass, two weeks have passed since the last large persistent slab avalanche was observed in the Northwest Mountains. The most suspect areas for triggering another persistent slab would be a trigger point or somewhere the slabs thin to below average in depth. These areas are more common in steep or extreme terrain where the snowpack may vary in depth more dramatically across the terrain.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–2.5

    Old, hard slabs 2–3+ feet thick linger over buried weak layers but are becoming increasingly stubborn to trigger and less common. Without obvious warning signs, avalanches are most likely triggered where the slab is thinner and easier to impact the weak layer below. The most fragile layers are buried in the middle and lower portions of the snowpack on northerly aspects. Persistent slab avalanches can propagate widely and be remotely triggered from adjacent low-angle terrain. One way to reduce the chance of triggering is by avoiding steep terrain with a thin or variable snowpack, such as rocky areas, rollovers, or places where winds have created uneven slab thickness. Triggering is the least likely in areas with a consistently deep snowpack across the terrain. 

    This was the last Persistent Slab avalanche observed in the NW Mountain FX area. It released ( 2/28) below a cornice on a steep face that has avalanched multiple times this winter. 

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    In steep terrain, keep an eye on the snow surface as it warms through the day. If you find a few inches of wet snow, you could trigger a small wet loose avalanche. These conditions will be more likely in rocky terrain, where the snow will heat up faster. Westerly winds may keep the snow surface more frozen on some wind-exposed terrain features, and increasing cloud cover later today will also limit surface warming.

    There is a very isolated chance for wet slab avalanche conditions to develop. Shoulder aspects, east and west, have been the most suspect. If you find your boots sinking deeply into wet snow on these aspects, it means you have overstayed your welcome in steep terrain. 

    An example of a wet loose avalanche that ran out of steep rocky terrain early this week. Photo: Travis Guy

Avalanche Discussion

A fresh weekly summary just came off the press. You can read the detaild version here, or watch the highlights here. 

We had another decent freeze last night that will create a nice window for spring skiing and riding on southerly facing terrain this morning. High temperatures are forecasted to climb into the low 40s at 11,000ft today, but increasing cloud cover should keep a cap on warming snow surfaces. The cloud forecast is a little messy. Some outputs show a mostly cloudy sky developing before noon, while others hold those clouds off until afternoon. Aiming for SE-to-S facing slopes would be more reliable than SW-to-W facing slopes, which may have more variable warming as cloud cover increases. Snow quality on northerly facing slopes is often ugly and uninviting after a rain event in February and multiple wind events affecting snow surfaces, as recently as the extreme wind event that occurred on Tuesday night. 

The recent Whetstone avalanche is the first persistent slab avalanche that we have documented in the Southeast Mountain forecast area, since a small slab was human-triggered on Snodgrass Mountain on March 4th, or other large avalanches occurred across both forecast areas in late February. Outside of our forecast area, there were several destructive avalanches that ran above Conundrum Creek around 3/6. Closer to home, past field work has documented the most concerning snowpack structures along the eastern side of the forecast area. Brush and Cement Creek areas, which typically had the weakest layers going into the February storms, now have thinner slabs that remain more susceptible to human triggers and thinner rain crusts in the upper snowpack.

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