Bulletin d’avalanche

Rattlesnake

West Central Montana Avalanche Center
Voir sur la carte

Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
Open full map
Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering a fresh wind slab on west aspects at upper elevations is possible today. Previous wind slabs are less reactive, but there is still potential to encounter an older wind slab on east aspects.  If you see recent wind loading or experience cracking and collapsing, stick to slopes under 33 degrees.

The storm is over, but exposure to bitter cold temperatures could make even a small injury dangerous.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Strong east winds for the past 24 hours have built wind slabs onto west aspects that were previously stripped earlier in the week. These fresh wind slabs may be sitting directly on crusts. These crusts can act as a smooth bed surface for avalanches causing them to run further than expected. Wind slabs remain a possibility on east aspects today, although sensitivity has decreased. 

    There is a large amount of snow available for transport, especially in the northern half of the forecast area around Seeley Lake and the Rattlesnake. There, 3-4 feet of snow is available for transport.  Across the Bitterroot, between 1-2 feet of fresh snow is available for transport. In the Lost Horse drainage yesterday, 1.5-2 feet of fresh snow was found in the upper part of the drainage. Snow totals for the storm varied across individual mountain ranges and zones. Areas with more snow available for the winds will have increased slab formation.

    Wind slabs will often appear as smooth rounded features. If you see evidence of recent wind loading or experience cracking or collapsing, stick to slopes under 33 degrees. 

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Steady winds and large amounts of snow available for transport have built large cornices along ridgelines. Cornices are potentially now large, overhung, and dangerous. Earlier this week in the southern Bitterroot, cornices were failing naturally and breaking into old cornice that was weeks old.

    Give any cornices respect and space. Cornice often breaks back further than expected. If you are traveling along ridgelines, make sure you know where the actual ridgeline is and avoid walking on cornices.

     

Avalanche Discussion

A winter storm put down 3-4 feet of snow in the Rattlesnake and Seeley Lake between Friday and Tuesday. Totals in the Bitterroot were less, with most areas receiving between 1-3 feet of snow. Now the storm is over, and cold temperatures have arrived. Expect lows down to -10f today around Seeley lake, with gradual warming as you move south through the forecast area. 

Winds shifted over the course of the storm. There was more than ample snow throughout to create wind slabs. At times, very strong winds reached down into mid elevation or normally sheltered terrain creating wind slabs in areas where you would not commonly expect to find them. Yesterday, winds shifted to a strong east wind, transporting snow that was previously deposited on east aspects back to west aspects. How much slab is left on the east aspects is unknown, but some probably remain. Be suspect of wind slabs on all aspects along ridgelines and at higher elevations today as wind slab may still exist on all aspects. 

Sensitivity in the storm snow has significantly decreased. Patience pays off when dealing with storm slab instability. Areas where you were likely to trigger an avalanche just a few days ago, have decreased to possible. You may still encounter lingering storm slab on convex rollovers.

 We did not receive any reports of avalanches triggered yesterday. With the good visibility yesterday, observers were able to see a few wind slab avalanches that failed naturally during the storm a few days ago. 

Make smart travel decisions with the weather today. A small avalanche or broken equipment could have serious consequences with temperatures this cold. Today is not the day to be stranded in the mountains. 

After a big week of storms, today may be the first day with good visibility. Take advantage of it and submit an observation of what you are seeing! We would love to hear about any avalanches you see, regardless of age or size. Tell us how much fresh snow you are finding or how strong the winds are blowing. We rely heavily on your observations to provide the most accurate forecast possible. 

Ski and ride safe.

Régions couvertes