Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist as recent snow sitting on a poor bonding interface is rapidly loaded with new and wind drifted snow. Soft slabs 2-3 feet deep will be easy to trigger in steep terrain above 7500'. Use conservative terrain choices and assess the stability of recent snow very thoroughly while traveling in and around avalanche terrain over 30°.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Large amounts of recent snow in the last week (since Feb 3rd) have formed soft slabs 2-3 feet deep. These slabs lie on a variety of poor interfaces across all aspects and elevations with weak, sugary facets and crusts mixed in. Continued snowfall and increased temperatures with clear skies yesterday formed this recent snow into more firm, cohesive slabs that will be easy to trigger today on steep slopes over 30°. Avalanches yesterday provide a clear picture that this snow is unstable. These avalanches can be triggered remotely from gentler terrain above, below, or beside steep slopes as seen on Four Pines. 

    Wind slabs have formed from south to west winds primarily above 8500’ on leeward slopes on NW-SE aspects. Areas where you find wind drifted snow will be deeper and more sensitive to triggering. Look for signs of wind drifted snow such as distinct hardness changes, large pillows/drifts, and altered snow surface texture. Areas of concern will be along ridgelines and open/exposed terrain. 

    Large remotely triggered avalanche on Four Pines just outside the JHMR boundary highlighting the poor new to old snow interface. 

    Photo: Josh Pope

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Today we have transitioned from a persistent to deep persistent slab problem. Above 7500’ hard slabs 3-5 feet deep lie above weak snow formed in December. Although the likelihood of triggering is decreasing, the possibility remains. Recent snow has added stress to these weak layers. Triggering a deep slab avalanche is most likely where the overlying slab is thin and riders can impact the weak layer. Any terrain with an overall shallow snowpack is concerning including very steep, convex, rocky and heavily wind affected slopes. Avalanches involving new snow could step down to these deeper layers in steep and sustained terrain.

    The most recent persistent slab avalanche that was remotely triggered Feb 3rd south of Teton Pass in the middle elevations. Crown visible through trees.

Avalanche Discussion

Winter is Back!

Since Feb 3rd the zone has received  28-46” of snow with 2.52-4.28” of SWE, aka snow water equivalent, (Surprise Meadows and Rendezvous Bowl data). All this new snow sits on a variety of poor new to old snow interfaces, with a stout crust sandwiched between facets on W/S/E aspects. On northerly aspects in higher elevations there are just weak, sugary facets. Yesterday slightly warmer temperatures and solar influence altered the quality of this recent snow into more of a firm, cohesive slab as skies cleared (hot pow). This slight change in hardness within the recent snow has a large influence on avalanche behavior, making it easier to trigger. This is also true where S to W winds of inconsistent intensity have formed firm wind slabs. The best way to manage these problems is stick to conservative lower angle terrain. Otherwise carefuly assessment and knowledge of the recent snow and bonding will be necessary. Performing quick hand shear tests is a great way to assess the reactivity of recent snow. We’ll see how cooler temperatures today influences the reactivity. In addition, some areas of the Tetons did not experience clear skies yesterday. Pay attention to changing conditions if skies clear today as solar influence can increase reactivity, especially on sunny slopes. 

As you noticed we transitioned to a deep persistent slab problem. The December drought layer buried 1/4 has been seriously tested by rapid loading as it gets buried deeper. We haven’t seen any activity this week besides Point 8724. This doesn’t mean we are totally clear. The step down potential of triggering a storm slab is real, especially in thin, shallow areas. Probing for hardness changes through this weak interface can provide an idea of the depth of the overlying slab. The hardness change from hard to soft will be noticeable. Watch out where it's thin. 

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