Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
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

The avalanche danger will increase throughout the day with rapidly warming temperatures. Start the day by sticking to slopes under 35º and avoiding convexities. Step back to lower angles and out of avalanche terrain as temperatures rise. Heavy snow, rollerballs, and pinwheels are signs the snowpack is destabilizing.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    The snow on all aspects will be affected by rising temperatures. Where the sun hits, warming will be very rapid. 

    Wet loose avalanches are likely, and wet slab avalanches are possible. Avalanches will be large enough to bury, injure or kill a person.

    One to two feet of new snow sits on facets over the crust. As the snow gains density and moisture, it may release as large slab avalanches. The wetness and potential size of these will increase throughout the day.

    Plan your day to get off avalanche slopes early. Shaded aspects may stay dry longer, but everything will eventually get wet today. 

    As the roller balls start, start your move to lower angle terrain. If the snow is wet and sloppy, increase your caution. 

    Plan your exit from the mountains, so you are not passing under or across avalanche terrain late in the day. 

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Wind slab remains a concern today and may become more touchy as warming temperatures destabilize it. 

    Windslab is widespread and extends further down slopes than normally encountered.

    Wind sculpted snow, wind lips, cornices, hollow-sounding snow, and broad drifts are all indications of wind slab.

    Avoid wind-loaded start zones over 35º, step back to lower angles as temperatures rise.

    Watch for red flags such as shooting cracks and natural avalanches.

  • Cornices

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

    There are massive cornices out there. They just received a fresh load with the last snowfall and wind. 

    Today rising temperatures and sun will rapidly warm and destabilize cornices. 

    The likelihood of cornice fall will increase throughout the day.

    Cornice fall is unpredictable, can be destructive, and may trigger larger avalanches as it falls on wind loaded slopes. 

    Stay well back from the top edge as cornices can break farther back than expected, and avoid being below. 

Avalanche Discussion

On average, Monday and Tuesday's storm brought one foot of snow to the forecast area. The central Bitterroot was under the faucet and received up to two feet. SNOTEL totals show 0.9" SWE at the North Fork of the Jocko, 1" SWE at Stuart, 1.3" at Lolo Pass, 2.2" SWE at Twin Lakes, and 0.9" SWE at Stuart Peak.

Winds were sustained above 25 mph for over 36 hrs, with gusts to 66mph. Winds moved considerable snow. Variable conditions exist at upper elevations, some windward slopes are scoured down to crust, and highly sculpted windboard exists in other areas. 

A widespread avalanche cycle occurred, with natural slides observed throughout the forecast area, many still failing yesterday. A thin layer of near surface facets under the new snow is likely a contributing factor. As temperatures warm today, these facets could fail as the snow gains density with the warmth. Avoid slopes over 35º and convexities to start the day. Dial it back to mellower terrain as temperatures rise.

Today, the freezing level will rise to 11000 feet, and temperatures could reach 54º at 8000'. All aspects and elevations will be affected. The avalanche concerns will quickly transition to wet problems. The crust under the new snow is a solid, slick sliding surface. If conditions are warm enough water will readily pool here, increasing the risk and size of wet slab avalanches.

For the most part, avalanches are not possible below 6000’ due to lack of snow. The exception is the Lolo Pass area and sections of the Seeley Lake zone, where the snowpack extends to lower elevations. 

With warmer temperatures forecast for Friday, and potentially no freeze tonight, the avalanche danger will continue to rise. Take care in the mountains today, and exercise extra caution tomorrow. 

Wet problems are hard to predict and don't respond to standard snowpack tests. The best strategy is avoidance. As the surface snow warms up, move out of avalanche terrain. The standard advice is to seek shadier aspects, but they will likely have wet problems today as well.

Saturday will be our final standard avalanche forecast for the season. We'd still like to receive your observations. They are a great resource to us and other recreationists. Please submit them here.

Ski and ride safe

Regioni coperte