Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

The Bitterroots lacked a refreeze last night, and with strong southwest winds and rain up to 6,000 feet, dangerous avalanche conditions will develop. This is a good day to keep your terrain selection simple and avoid wind-loaded slopes with angles over 35 degrees. Rain on snow will increase the risk of wet avalanches. Plan your exit from the mountains to not pass under or across wet saturated slopes late in the day and stay alert for overhead hazards. 

Lawinenprobleme

  • Wet Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Temperatures remained elevated last night, and snow levels are forecasted at 6000 feet for the southern Bitterroot and 5,500 feet for the Central Bitterroot today. Temperatures could rise as high as 48°F. The risk of wet avalanches will increase for low and mid-elevations as rain and melting snow saturate the snowpack. 

    Water trickling through the snowpack could lubricate the icy rain crust formed earlier this month, causing it to release as a slab avalanche on the crust—elevation between 5,000 and 6,500 feet with the thickest crust is most suspect. 

    Rollerballs and sinking past mid-boot in wet snow signify wet instabilities are forming nearby. Avoid slopes over 35 degrees and stay alert for overhead hazards. 

    (03/12/2022) A large debris pile from a wet loose avalanche in the Bass Creek drainage from this weekend.

    Photo: Andrew Borden

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Strong winds out of the south and west will grow wind slabs on east and northerly aspects throughout the day. Warm forecasted temperatures will aid in slab formation. 

    Look for clues like wind textured snow, drifts, and wind lips to indicate wind direction. Hollow-sounding snow and shooting cracks are signs that wind slabs are nearby and reactive. 

    Avoid wind-loaded slopes with angles over 35 degrees.

    Large cornices linger over east-facing ridgelines. They deserve space and respect. Avoid traveling underneath them.

    (03/12/2022) A snow biker triggered a  wind slab on the leeward side on an east aspect at 8,000 feet just outside our forecast area in the Copper Creek drainage near Lincoln. The debris pile was large enough to bury a person. 

Avalanche Discussion

Over the weekend, we received multiple reports of unstable snow. On Saturday, a snow biker triggered a large wind slab avalanche on an east aspect at 8,000 feet just outside our forecast area in the Copper Creek drainage near Lincoln. A group reported propagation, in Bass Creek, on near-surface facets sitting on the rain crust on an NW aspect at 6,800 feet as well as whumpfing on lower angle terrain and loose wet activity. Sunday, a group was surprised by multiple signs of instability, including a prominent collapse of a dense wind slab on a north aspect at 6,300 feet in the Mill Creek drainage. Fortunately, no one was caught or injured. 

The likely culprit to this weekend's instabilities is near-surface facets sitting over the prominent rain crust from the first week in March. Colder temperatures last week allowed the snow that fell over the crust to recrystallize and become less dense. This weekend's wind and warm temperatures permitted a slab to form over these weak layers. 

So what can we expect for today? In general, warm temperatures and light winds over the last 48 hours have allowed these faceted layers to round and bond to the underlying crust in most places. However, rain and heavy snowfall could reactivate these layers, and there is always a fair amount of uncertainty with buried weak layers and how long they will persist. Given the forecasted level of moisture (up to .53 SWE) and snow levels (5,500 to 6,000 feet), and lack of refreezing last night,  I suspect water and possibly heavy snow will cause some activity on this layer in the Bitterroot. It will likely remain small and isolated to pockets on north and easterly aspects for elevations above 6,500 feet. 

We've tracked reactive buried facets on north slopes above 8000' in the Southern Bitterroot. They are buried around 3 feet deep, getting deeper and likely healing. But the potential still exists for a wind slab or cornice fall to step down to this layer—exercise extra caution in this zone. 

Fresh wind slabs and wet instabilities are the primary concern today. If you plan to travel in the backcountry, take precautions to avoid wind-loaded or wet and saturated slopes.

Please let us know what you are finding out there. You can submit observations here.

Ski and ride safe.

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