Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Overall, low avalanche danger exists throughout the Bitterroots except for Gash and the surrounding drainages, where the hazard is moderate due to the possibility of large persistent slab avalanches. Avoid slopes over 35º in this area. Windslab is stubborn, but reactive pockets may be lingering in isolated areas throughout the forecast zone. Stay alert for signs of instability, such as shooting cracks in steep wind loaded start zones at upper elevations. Otherwise, enjoy the soft snow and more manageable temperatures.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3

    A crust facet combo is buried up to three feet deep in the Gash area. 

    Multiple crowns from natural avalanches were spotted in the Bear Creek drainage. These likely released between last Thursday's wind event and Sunday’s storm. 

    The extended column test showed good strength but a high likelihood of propagation around 7000’ at Gash.

    Persistent layers like this can remain a problem for a while and will likely not give warning signs before failing. 

    The extended column test may help you assess this layer. However, tests on layers such as this can sometimes produce false stable results. 

    If you triggered a slide on this layer, it would be large and destructive. 

    It’s best to avoid slopes over 35º and convexities at Gash and in surrounding drainages until this layer bonds further. 

     

    (2/23/2022) null Photo: Todd Glew

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Windslab is stubborn, but reactive pockets may be lingering in isolated areas throughout the forecast zone.

    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.

Avalanche Discussion

After a couple of days of frigidly cold temperatures and strong east winds, the temperature has begun to moderate, and winds have shifted back to westerly. Despite the bitter cold yesterday morning, diminishing winds, rising temps, and clear skies made for a beautiful day in the mountains. 

We’ve got a couple more nights of sub-zero temperatures ahead of us, but days should reach the upper teens and low twenties during the day. Light snow showers are possible today, but accumulations will be minimal.

Yesterday in the mountains, we found overall stable conditions throughout the forecast area. Instabilities are mostly isolated to last weekend's new snow and are inconsequential. Where Monday and Tuesday's winds drifted the snow, it has bonded well, and we found minimal sign of reactive windslab. The Bitterroot, Lolo, and Seeley zone showed minimal wind effect, suggesting that east winds did not reach high speeds. The Rattlesnake had evidence of significant scouring and snow transport from east winds. Cold temperatures and wind have created near-surface faceting in the upper 6 inches of snow, but this isn’t an issue until it gets buried and becomes a weak layer. 

The exception to the mostly stable snowpack was found at Gash, where a layer of facets buried under wind drifts from last Thursday's wind event propagated 32” deep. Visible from the top of Gash were large crowns in the Bear Creek drainage. 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, it would be large and destructive.  It’s best to give this some time to bond before stepping into prime avalanche terrain in the Gash area and surrounding drainages. See the observation here.

We love all the public observations we’ve received this year. Many thanks to the folks who’ve sent them in. You can submit observations here. 

Ski and ride safe

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