Lawinenlagebericht

Rattlesnake

West Central Montana Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Wet loose avalanches are possible today with rising temperatures. Sun on snow will accelerate the warming and increase the danger. Today, as temperatures rise and rollerballs start, move to shady aspects and higher elevations. Avoid slopes over 35º and overhead hazard late in the day. Avalanches on the March 1st crust/facet combo remain a slight possibility. Avoid convex and unsupported slopes over 35º

Lawinenprobleme

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    Wet loose avalanches are possible today as temperatures rise above freezing at most elevations throughout the forecast area. 

    If the sun makes an appearance this afternoon, it will accelerate snow warming, and the risk of wet loose avalanches will increase. 

    Wet loose slides will most likely be small today.  However, they pose a problem if encountered above or in terrain traps where they can gather the depth to push you over or into hazards. 

    As the rollerballs start, the snow gets wet, and the sun comes out, move to shady aspects and higher elevations. 

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

    (3/21/2022)

    Wide spread wet loose debris from Saturaday's warming

    Photo: Jeff Carty

  • Persistent Slabs

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

    That pesky March 1st crust and facet combo has been with us for a while, and remains a concern, although time and warm temperatures over the weekend have aided bonding. Yesterday in the Rattlesnake, the likelihood of triggering a slide on this layer was low. In the central Bitterroot, isolated pockets of reactivity could be found, while other areas showed good bonding. Similarly, the southern Bitterroot showed signs of improved bonding on Sunday. 

    The problem can be found at elevations where the March 1st rain crust exists, and temperatures have remained cool enough to preserve the slab and facets, between about 6000’ and 8000’. Areas with a supportable crust at the surface are not a concern, shaded aspects are more suspect. 

    While the likelihood of triggering this problem has decreased, it hasn’t gone away. Steep convexities, unsupported slopes, and shallow spots may be trigger points. 

    It’s worth digging and performing an extended column test or propagation saw test before committing to any slopes over 35º.

    Avoid convexities, choose planar and supportive slopes to minimize risk.

    (3/18/2022)

    Small slab sliding on the March 1st crust/facet layer

    Photo: Jeff Carty

Avalanche Discussion

Since the last forecast, we’ve had quite a swing in temperatures. Saturday saw highs of 49º above 6000’, Sunday dropped to 19º, and temps stayed cold yesterday above 5000’. 

The snowpack was widely affected by Saturday's warmth with rollerballs found on all aspects in the Rattlesnake and a melt-freeze crust extending above 7000’ in the central Bitterroot. 

A few inches of snow has fallen since Saturday night with some areas receiving more than others. It hasn’t been enough to affect avalanche conditions.

Winds blew hard Sunday and moved considerable snow. They had died down by Monday morning and remain mostly light today. Wind slab was not reactive yesterday, but as always, you can probably find isolated pockets of wind slab at upper elevations. Cornices grew considerably over the weekend and were reactive yesterday. Cornice fall could become a problem with warming temperatures and sun. Avoid being below cornices and stay well back from the top. These giants can fall unpredictably. 

Today we can expect the temps to rise again and be elevated for the rest of the week. Temps are rising above 32º at most elevations today but will drop below freezing tonight. As the week progresses, temperatures may stay elevated overnight, and the avalanche hazard may increase with rain to 8000’ and wet snow problems.

Your observations continue to be a great help to forecasters and other recreationists. Please keep submitting them here.

Ski and ride safe.

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