Avalanche forecast

Avalanche forecast

Payette Avalanche Center
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Avalanche danger

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Out of date — this forecast expired last year.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

Highlights

Today's avalanche danger reflects a higher degree of uncertainty around the storm this morning and recently buried rain and melt-freeze crusts. Triggering a wind slab avalanche up to one foot thick is likely today above 7000' on east-facing slopes. Recent crusts and crust/facet combinations could make wind slabs more reactive than normal. Dry loose avalanches could be in store with new snow sliding on a recent rain crust.

Avalanche problems

  • Wind Slabs

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

    3-6" (0.5"SWE) of snowfall overnight along with W/SW winds will create fresh wind slabs today. Another few inches of snowfall is possible this morning, so totals could be in the 4-8" range. W/SW winds have been gusting over 30 MPH this morning and are forecasted to increase throughout the morning. Winds should shift from W/SW to W/NW today. Expect to find wind slabs one foot thick on easterly aspects above 7000'. Wind slabs could be extra sensitive today with recently buried rain and melt-freeze crusts. Stay attentive to crossloading and a changing wind direction loading slopes across the compass. Watch for visual clues like shooting cracks from your skis, board, or sled. If you notice a change from soft and powdery to stiff and "slabby", be heads up for wind slabs. Look for drifts, dunes, or pillows to indicate the presence of a wind slab.

    Solar Aspects

    Yesterday, I observed small, near-surface facets above a 3cm thick melt-freeze crust that formed and was buried Wednesday (03/19). You can read that observation here. This isn't quite a persistent slab problem yet, but that could be forming with today's storm. Wind slabs on solar aspects today could behave more like a persistent slab if this crust/facet combination is present. I would have my guard up with this new wind slab on aspect E-W on the south-side of the compass. If you're seeing obvious red flags like cracking and collapsing, then assume the crust/facet combination is present and find another slope to be on.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Yesterday, rain and freezing rain left a thin crust at the surface across all aspects up to 7600' (potentially higher). If this crust is strong enough to provide a bed surface, new snow today will likley not bond well and create small, dry loose avalanches. If the clouds break this afternoon and the sun pops out, this could drive a round of loose avalanches on south-facing slopes. Dry loose avalanches may seem benign and manageable, but they can often catch experienced professionals off guard. Be prepared to manage sluff in sustained terrain over 35 degrees, especially near terrain traps like gullies and above big rocks/cliffs. 

Avalanche Discussion

Uncertainty

Today's avalanche danger reflects a higher degree of uncertainty around several factors:

(1) Weather forecast. As of this morning, it looks like we received slightly lower storm totals than anticipated. Snowfall is expected to taper off before mid-day today. Has the precip turned off or are there a few more inches in store? If the storm drops several more inches, wind slabs could be more stout than expected.

(2) Friday's rain crust. Yesterday, rain and freezing rain left a thin rain crust at the surface up to 7600' (potentially higher). This crust was across all aspects and elevations. Will this rain crust be strong enough to provide a bed surface for the new snow to slide on? If so, dry loose avalanches will be possible anywhere this rain crust is present. Even a brief break in the clouds with only partial sunshine can heat up the new snow to create loose avalanches on solar aspect, especially if there's a slick bed surface.

(3) Melt-freeze crust from Wednesday. Yesterday I observed small, near-surface facets above a 3cm thick melt-freeze crust that formed and was buried Wednesday (03/19). You can read that observation here. This was on a SE aspect and I observed propagation in ECTs (ECTP 6 & 9) 6" down on the NSF above the melt-freeze crust. This leads us to believe aspects that received direct solar input on Wednesday (E, SE, S, SW, W) could be harboring this crust/facet combination. This isn't quite a persistent slab problem yet, but that could be forming with today's storm. Wind slabs  on solar aspects today could behave more like a persistent slab if this crust/facet combination is present.

Uncertainty requires wider margins of safety and it warrants further investigation. If you're out in the mountains, spend a few minutes to dig down and look at how the recent storm snow has set up. Questions to ask are: how is the new snow bonding to recent interfaces, including crusts; and are you finding the crust/facet combination on solar aspects? I would want to answer these questions before jumping on steep slopes today.

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Interested in some continuing education? Check out some recent research from Ian McCammon and Kelly McNeil on Risk Management Trends in US Backcountry Avalanche Accidents.