Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The danger will rise to Considerable as wind speed and snow intensity increase late this morning and into the afternoon. Fresh, sensitive wind drifts will grow in size and extent throughout the day. Underneath these drifts, weak snow buried 3+ feet in depth continues to pose a threat. To reduce your risk, steer clear of obvious drifts and slopes where the wind has stiffened the snow surface. 

Avalanche problems

  • Wind Slabs

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

    Since the beginning of the week, the Teton zone has picked nearly a foot of new snow, though it came hand-in-hand with moderate to strong W to SW winds. As a result, wind slabs have formed on the lee sides of ridges and other exposed terrain features. Over the past several days, several small natural and triggered wind slab avalanches have been reported here. 

    Warm temperatures yesterday have helped these wind slabs bond to underlying snow surfaces, but more snow and wind today will create a fresh batch that may be sensitive to your weight. Fortunately, these wind slabs will be easy to identify and smaller in size. I suspect sensitivity to also be short-lived. 

    Watch for snow that is denser than snow found on wind-sheltered slopes and tell-tale clues such as surface texture and a pillowed, drifted appearance. In the alpine terrain of the Tetons (9,500 feet and above), spindrift trickling down cliffs or funneled into narrow terrain features often forms slabs. Avoid steep slopes or consequential, exposed terrain where you find these indications of recent wind loading.

    (2/6/2023)

    Two separate parties were involved in avalanches in an exposed area outside JHMR yesterday. This illustrates the importance not only of group communication and preparedness but also choosing terrain that is appropriate for a given hazard (Ralph's Slide observation).

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Triggering a 3+ foot thick persistent slab avalanche is unlikely. The weak layers we've struggled with all winter have not gone away, but they've become less reactive to the weight of a skier or rider. Due to their depth, they've also become very difficult to impact with your weight-- however, this depth is a broad range across various aspects of the zone and remains a thick layer of facets on many middle and upper elevation slopes. Don't completely write them off—especially since the consequences of triggering a large persistent slab would be catastrophic. I continue to be wary of very steep (over 35 degrees), alpine terrain that is more likely to have thin spots where your weight may reach the weak layers.

    Deep Persistent Slab: Areas on the southern half of the compass in the middle and upper elevations harbor deeply buried weak snow from late November. With deeply buried weak layers, it's important to avoid thinner areas where you can more easily impact the weak layer. You can reduce your risk of triggering any and all of the above avalanche problems by avoiding: 

    • Wind-affected terrain: The wind can create thinner spots where the weak layer is closer to the surface. These are often connected to wind-loaded areas where there is more load on the weak layers.
    • Steep, rocky slopes: Rocky or "alpine-like" terrain typically has shallow areas where your weight can more easily affect buried weak layers.

Avalanche Discussion

Today's forecast order comes with a hefty dose of uncertainty sauce, and you are the chef. If snow and wind totals pan out as predicted in the alpine, I suspect you could buy an avalanche, and hazard will increase throughout the course of the day. If they don't pan out, then expect the overall hazard to be less. The wind is probably one of our least favorite winter weather factors, and lately, it has been the primary force behind our avalanche conditions. In areas where these wind slabs form atop snow surfaces that aren't persistent weak layers, such as softer new snow, older wind slabs, and crusts, the period of instability is often short-lived. Warmer temperatures can help to speed up the process of stabilization. The trouble is that consistent winds over the past several days formed fresh, touchy wind slabs even as old wind slabs stabilized.

The more complex issue with recent wind loading is where the wind slabs are adding additional weight to buried persistent weak layers. Where our snowpack remains shallow and especially weak—for example, the windswept areas of the Greys River and Togwotee—the recent wind loading is more hazardous. This problem is likely to persist longer than the pure wind slab problem and has the ability to produce a much larger avalanche.

Fortunately, areas with recent wind loading are easy to identify with in-the-field, tangible observations. The snow surface on wind-affected slopes usually has a different texture and will be denser and more cohesive than the snow found on sheltered slopes. Keeping your eyes open for these clues (well, keeping them open at all with the predicted winds today), and avoiding steep slopes where you find them, will help you avoid most of the avalanche risk that currently exists in our area. This is especially true if you find yourself in alpine areas or where the snowpack remains on the shallow side. 

So there's your recipe: start with a base knowledge of the snowpack in areas you frequent, add a splash of reading the forecast and adjusting it for incoming weather, sprinkle with the right partners and good communication—and mix all of the above in terrain that fits your assessment. 

 

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