Bollettino valanghe

Seeley Lake

West Central Montana Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Wet problems persist. Lower elevations have not refrozen overnight and may be saturated. There is a risk of wet slab avalanches at these elevations. Where the snow refroze stability is good until it thaws again today. Some upper elevation areas may be crust-free, and except for isolated wind slab, stability is good. 

Problemi valanghivi

  • Wet Slabs

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

    Elevations below 5000’ may not have refrozen last night, were saturated by rain yesterday and remained above freezing for 24hours.

    The snowpack may be isothermal and lack any cohesion. 

    This is where the greatest avalanche hazard exists today. 

    Stay off wet saturated snow on slopes over 30º and stay well away from the base of steep slopes, including road cuts and other short slopes not normally considered a hazard.

  • Wind Slabs

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

    Isolated wind slab could be triggered at ridgetop in upper elevations.

    Winds varied throughout the forecast area yesterday, with snow transport occurring in some areas. Overnight winds were light to moderate out of the southwest, with strong gusts capable of moving snow. The Missions and Swans saw higher windspeeds, and wind slab is more likely in these ranges.

    Avoid leeward slopes over 35º where evidence of snow transport, such as fresh wind lips and cornices, exist.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–3

    The deep persistent slab in the southern Bitterroot is being downgraded to unlikely to produce avalanches. It didn’t react to last week's loading, and as far as we know, it didn’t fail with yesterday's elevated temperatures indicating good strength. The warm temperatures, combined with the depth of the snowpack, are helping bond the problem layer. Unless we find strong evidence to the contrary, we will remove this layer from the problem list on Saturday.

Avalanche Discussion

What a wet one it was yesterday. The freezing level rose above 8000’. The southern portion of the forecast area was warmer than the north, but it was wet everywhere. The snow line hovered around 6000’; below this received rain. Temperatures rose as high as 38º at Saddle Mountain at 7940’, 40º at Twin Lakes at 6400’, and 35º Stuart Mountain at 7400’. Up to 3” of new snow fell at middle and upper elevations. 

This morning temperatures have barely dropped, with 33º on Stuart and 29º at Saddle. Some areas have temperatures indicative of an inversion, with 26º in Sula and 23º in Seeley lake. Elevations below 5000’ and above the cold valley bottom have likely not refrozen. This elevation was saturated by rain yesterday and has remained above freezing for 24 hours. The snowpack could be isothermal and lack all cohesion. This is where the greatest risk of avalanches is today.

Where temperatures dipped below freezing, there is likely a stout crust up to about 6000’ in the northern part of the forecast zone and 8000’ in the south. The freeze will lock up the snowpack somewhat, but rising temperatures today will again soften the snow surface. Partially cloudy skies may limit solar warming. If you start sinking into wet snow past mid-boot and see roller balls beginning, move to lower angle slopes.

Take extra care in the Rattlesnake, where temperatures remained above freezing overnight. The snowpack is mostly devoid of problem layers, making slab avalanches lower likelihood, but the risk of wet loose slides will increase today. Isolated basal facets could become more reactive with prolonged warmth.

At elevations above the crust, where temperatures dropped below freezing, the snowpack has consolidated well. Yesterday's warm temperatures helped. It is unlikely to trigger a slab, but practice normal cautions such as using stability tests, watching for red flags, and skiing one at a time. 

Ski and ride safe.

Regioni coperte