Bollettino valanghe

Rattlesnake

West Central Montana Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

While peak instability from the last storm has passed, it is still possible to trigger an avalanche in wind loaded terrain or areas with persistent weak layers.  Likely areas are ridge tops and complex terrain like cliff bases and cross loaded gullies.

Avoid slopes with smooth pillows or hollow feeling slab. If you see collapsing, cracking, or whumfing, stick to terrain under 35 degrees.

Problemi valanghivi

  • Wind Slabs

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

    Shifting wind directions and strong winds built wind slabs on multiple aspects Saturday and Sunday. Multiple natural wind slab avalanches were reported Sunday in the Rattlesnake zone on south through east aspects. These slabs are becoming increasingly stubborn, but if triggered, could release up to 3 feet deep. High winds built slabs low on slopes, and avalanches releasing at cliff bases were a common trend Sunday.  Avoid slopes with smooth pillows or hollow feeling slabs. If you see cracking, collapsing, or whumfing, back off to slopes under 35 degrees.

  • Persistent Slabs

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

    Persistent weak layers of near surface facets or buried surface hoar are still present in isolated areas in the Rattlesnake. Lockwood Point had surface hoar buried 6-12 inches before the storm.  New snow Friday and Saturday bonded well to the existing snow, increasing slab thickness to up to 3 feet above any persistent weak layer.

    It is unlikely to trigger an avalanche on these weak layers, but it is still possible with the right trigger location, like a convex rollover or shallow area of the slab. Dig down, and if you find persistent weak layers, stick to slopes under 35 degrees. 

Avalanche Discussion

A powerful winter storm on Friday and Saturday brought strong shifting winds and heavy snowfall across all forecast zones. The Rattlesnake and Seeley lake zones received the most snow and the strongest winds. The weather changed Sunday and Monday to calm winds, blue skies, and frigid temperatures. Today, winds will be strong from the west, with the potential for an inch or two of new snow. During the last storm, we saw a natural avalanche cycle lasting through Sunday. Large natural avalanches were observed in the Rattlesnake and Bitterroot. Both ski and snowmobile triggered avalanches were reported in Seeley Lake throughout the weekend. 

Coming into today, peak instability from the storm has passed, and avalanches are becoming difficult to trigger. Observers Sunday and Monday mentioned a stubborn slab and difficulty getting cracking or movement. Despite the decreasing hazard, it is still possible to trigger an avalanche large enough to bury you. With the shifting winds, be suspicious of all aspects at the upper elevation and look for loaded features like pillows or hollow feeling snow. Strong winds can build slab low in start zones, and you do not know until you have already skied onto it. A common theme this weekend was slabs at the base of cliffs or rocks. 

Persistent slab hazard still exists in all zones, although stubborn and unlikely to trigger. In Seeley Lake and the Rattlesnake, surface hoar buried 6 inches at the start of the storm is now buried 1-3 feet deep. The best way to identify this layer is to dig in areas you are looking to ski or ride. If you find it, stick to slopes under 35 degrees. Basal facets and deep persistent slab in the southern Bitterroot remain a low probability but high consequence problem. 

 If you are traveling in avalanche terrain today, pay attention to your surroundings. Recent avalanches are the best indicator of instability. With new snow expected today, any avalanche you see is likely fresh. Avalanches on similar slopes to what you are looking to ski or ride is a red flag that overrides any snowpit or stability test.

Let us know what you see out there today by submitting an observation. If you see an avalanche, even if it looks old, please send us a picture! 

Ski and ride safe.

Regioni coperte