Lawinenlagebericht

Rattlesnake

West Central Montana Avalanche Center
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Lawinengefahr

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

Triggering an avalanche is possible today along ridgelines and wind loaded slopes. 

An increasingly stubborn wind slab has been buried by 1-3 inches of new snow, making detection more difficult.  If you see a smooth pillowy slab or experience cracking and collapsing, stick to slopes below 33 degrees. 

Wet loose avalanches are possible by afternoon as skies clear and temperatures warm. 

Lawinenprobleme

  • Wind Slabs

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

    On east aspects, there are between 1-4 feet of overlapping wind slabs. Overnight, 1-3 inches of new snow and west winds created a fresh layer of slab on top.  Strong west winds through Thursday built stout wind slabs below. Although yesterday's winds were strong, the amount of snow available for transport was significantly less. 

    It is becoming increasingly difficult to trigger one of the older slabs. Still, an avalanche in a fresh wind slab also has the potential to step down, resulting in a larger, more dangerous avalanche.  Yesterday, a skier had a close call with a wind slab stepping down in Birthday Chute outside Snowbowl when a wind slab stepped down, creating a large dangerous avalanche. 

    Watch for loading at convex breakovers, cross loading in gullies, or at cliff base.   

    Wind slabs can be identified by their smooth rounded appearance. Watch for shooting cracks, collapsing, or a hollow feeling slab. If you encounter any of these, stick to slopes under 33 degrees. 

  • Cornices

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Large and overhanging cornice growth along ridgelines will become an increasing concern. Give any cornice a wide berth, as cornices often break back further than expected. Warming temperatures today could lead to natural cornice failure.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–1.5

    Clearing skies and temperatures into the upper 30s will likely lead to wet loose avalanches on sunny aspects. Moderate winds may keep the snow cool enough at upper elevations to mitigate any warming, but in sheltered terrain, expect the snow to warm enough to move. 

    Watch for rollerballs or point releases off rocks and trees, as these are early indicators that conditions for a wet loose avalanche cycle are building. If you find yourself collapsing through non supportive wet snow, stay out of avalanche terrain and pay attention to what is above you. 

Avalanche Discussion

It has been a week of strong west winds and wind slab development. Last night, a new slab was added to the top of the layer cake with 1-3 inches of new snow and west winds building slab on east aspects. At this point, there are between 1-4 feet of wind slabs overlaying each other, all with different hardness and sensitivity. The slab at the bottom is increasingly stubborn but still not trustworthy. An avalanche in one of the top wind slabs has the potential to step down, as we saw in Birthday Chute yesterday when a skier had a close call. The wind slab problem is becoming difficult to manage and east facing slopes over 33 degrees are best avoided today. Along with the wind slab, there is now significant cornice growth along ridgelines. Some of these cornices are very large and overhanging. Stay well clear of the edge, as the cornice can break back further than anticipated. 

Today, skies will clear, and temperatures will rise. At upper elevations and in exposed terrain, steady winds will work to keep the snow surface cool, and wet avalanches are unlikely. In sheltered terrain or lower elevations, expect the snow surface to warm by afternoon, and wet loose avalanches will become possible. Warm temperatures can also contribute to natural cornice fall. Today is not a good day to hang out under a large cornice. 

We have removed the persistent slab concerns in Seeley and the Rattlesnake, as well as the deep persistent slab from the southern Bitterroot, from the problem descriptions. These layers are gaining strength and have been tested thoroughly over the past week without any reported avalanches. In the southern Bitterroot, there are still areas at upper elevation north aspects with weak basal facets. It is unlikely to trigger an avalanche on this layer but remains a low probability, high consequence problem.  In the Rattlesnake and Seeley Lake, any buried surface hoar was likely destroyed during the natural avalanche cycle in these zones last weekend. 

Let us know what you see today by submitting an observation.

Ski and ride safe!

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