Bollettino valanghe

Rattlesnake

West Central Montana Avalanche Center
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Pericolo valanghe

Sun
Alta quota
1 · Debole
Limite del bosco
1 · Debole
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

Generally, stable conditions exist throughout the Rattlesnake and Seeley Lake zone. Wind slab is growing on east slopes with increased west winds. Isolated pockets of reactive wind slab may remain on west slopes. Stay alert for signs of instability, such as shooting cracks. Avoid wind loaded pockets in steep start zones below exposed ridges and peaks. 

Problemi valanghivi

  • Wind Slabs

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

    Westerly winds have increased and are transporting snow onto previously scoured east faces. East aspects have been scoured down to crusts or contain dense windboard in many places. Both of these are slick sliding surfaces for newly developing windslab. Isolated pockets of reactive windslab may remain on west slopes.

    Upper elevation start zones, just below ridgelines with terrain over 35º, is the most likely place to trigger a windslab. 

    Stay alert for signs of instability such as shooting cracks and avoid pillows of wind deposited snow, especially where terrain traps such as steep gullies or cliff bands exist.

    (2/25/2022)

    Wind scouring

    Photo: Jeff Carty

  • Loose Wet

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

    With rising temperatures and clear skies today, loose wet avalanches are possible on solar aspects.

    These will likely be small but could knock skiers and riders off their feet or push them into terrain traps. 

    As temperatures rise throughout the day, stay alert for warming snow surfaces. If roller balls begin, start moving to shadier aspects.

     

Avalanche Discussion

The past 48 hours have continued the pattern of sub-zero nights and cold days. Temperatures were more manageable with highs of 14º at 7400’ feet yesterday. Skies have been clear, and we’ve had no new snow. Winds began to pick up out of the west yesterday, reaching 25 MPH at Point 6.  

Yesterday in the mountains, we found similar conditions to Wednesday, with the addition of increased wind transport at upper elevations. More evidence of recent avalanches was spotted in the southern and central Bitterroot and Swans. These are the isolated pockets of windslab discussed in the previous forecast. They are small but pose a problem in exposed terrain and with terrain traps. Cornices pose a problem as well, with one large cornice failure reported. Give cornices a wide berth when above and avoid spending time below. Except for wind slabs at upper elevations, conditions are mostly stable, with no layers of concern in the southern Bitterroot, Lolo Pass, the Rattlesnake, or the Swan. 

The exception to the mostly stable snowpack is found at Gash and the surrounding drainages. A layer of facets buried 32” deep is propagating in tests, and multiple crowns from large avalanches are visible from the ridge. These are up to 500’ wide, down about 3 feet, likely on the same layer propagating at Gash. Deeply buried facets are hard to predict, may not give clear warning signs, and can produce false stable results in tests. It will be hard to trigger this layer at this depth. However, if you did, the avalanche would be large and destructive. We don’t yet know the layer's full distribution. It’s best to give this some time to bond before stepping into prime avalanche terrain in the Gash area and surrounding drainages. 

Your observations help produce a more accurate avalanche forecast. You can submit them here. 

Ski and ride safe

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