Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
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

We are issuing a non regular scheduled forecast today for increased avalanche hazard.

It finally looks like winter, and excellent skiing and riding conditions can be found, but check your powder fever and recognize the increased avalanche danger today.

Human triggered avalanches are likely in wind loaded terrain at upper elevation. Triggering a larger persistent slab avalanche at upper elevations on north aspects is also possible. Look for red flags like shooting cracks, collapses, or recent avalanches. If you encounter these, stick to slopes under 30 degrees.

Avalanche danger is greatest in the central Bitterroot, where the most snow has fallen in the past 48 hours and avalanche danger at upper elevation is pushing toward the high rating.

Problemi valanghivi

  • Wind Slabs

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

    Winds for the past 24 hours have shifted from the southeast to the west. Overnight wind speeds were significantly weaker than forecasted, but still in the prime snow transport range.

    Expect fresh wind slabs 12-24 inches deep at upper and middle elevations today.

    Slabs will be deepest and most widespread on north through east aspects. In complex terrain like cirques or couloirs, shifting winds will be enough to create smaller wind slabs or cross loading on all aspects. In addition, high wind speeds often cause wind slabs to be built lower on slopes than usual.

    Wind slabs can be recognized by their smooth, pillow-like appearance, but they may not always be obvious when new snow covers them. If you encounter cracking, collapsing, whumfing, or the snow has a hollow slab-like feel to it, step back to terrain under 30 degrees.

  • Persistent Slabs

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

    It will be possible to trigger a larger avalanche, potentially breaking near the ground and taking out the entire season's snowpack today.  Multiple persistent weak layers of near surface facets, buried surface hoar, and isolated depth hoar on upper elevation north aspects exist in the snowpack. Until now, these layers have not been problematic as they have had no slab above them.  This storm is the first load these weak layers have seen, and how well they adjust is yet to be determined.

    Snowpits can be a useful tool for identifying areas with buried persistent weak layers, but don’t let a lack of unstable results in your snowpit tests justify jumping into avalanche terrain with poor snowpack structure.

    Collapses and whumfing are signs that the persistent weak layers are becoming reactive and fractures are propagating. If you encounter these red flags, stick to slopes under 30 degrees and do not linger underneath avalanche terrain. 

     

Avalanche Discussion

As the storm begins to exit our area this morning, we can add snowfall and snowwater numbers before the next system arrives tonight and tomorrow. Remember that the forecast area is large; some drainages likely received more snow than these totals. If you get out today, please let us know how much new snow you find in your travels. It helps us a lot!

The central Bitterroot has been the big winner so far, with 24 inches of snow and 1.9 inches SWE (snow water equivalent). 

Seeley Lake North Fork Jocko SNOTEL was next with 11 inches at 1.3 inches of SWE.

The Rattlesnake did not receive nearly as much, with storm totals closer to 6 inches of new snow and .5" SWE.

Avalanche danger today exists primarily on the north and east aspects, especially in wind loaded areas. Most south facing aspects have a very stout crust on the surface. Although not a primary avalanche problem today, slough management in loose dry snow will be important where new snow sits on crusts. Sloughs can run faster and further than expected on such stout crusts. 

This storm will certainly help with conditions, but remember that our snowpack is still thin. Hazards such as buried stumps, logs, and rocks are widespread and may be concealed under fresh snow. 

Please consider submitting an observation of what you see in the mountains. Even a simple photo helps forecasters better understand conditions and create more accurate forecasts.

Contact us here if you're interested in volunteering for a field day with the Avalanche Center. This is a unique opportunity to ski or ride with a forecaster and learn or grow your own snow and avalanche skills. 

Ski and ride safe!

 

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