Avalanche forecast

Mt Hood

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Another storm ramps up on Sunday with warming temperatures, increasing winds, and snowfall rebuilding dangerous avalanche conditions.  Complex wind patterns may make it challenging to predict where a potentially large wind slab lurks. Avoid steep wind-loaded slopes at upper elevations and use simple slope tests to evaluate slab potential in sheltered terrain.

Avalanche problems

  • Wind Slabs

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

    Another storm will bring increasing snowfall and winds to Mt. Hood. The danger near and above treeline will rise as increasing snow transport occurs. The new snow falling may be increasingly dense, so it might not take as much wind loading as normal to get reactive slabs to form. Anticipate SW winds to load typical aspects, but in some locations low-level E winds may push loading patterns onto atypical aspects. Clearing skies Saturday evening may allow snow surfaces to weaken, so make sure to check for slab structure (firm over less firm) and potential to propagate (with hand shears or small slope tests). As the storm ramps up and the visibility decreases, you should increasingly limit your terrain selection. You may lose the ability to look for visual clues such as wind-textured snow or the shape of rounded snow pillows. Blowing snow will be your primary indicator for decreasing stability and where all the snow is getting piled up. Shooting cracks and punchy layering should also remind you to avoid wind-loaded slopes steeper than 35 degrees.

    Example: Blowing snow, drifts, and textured surfaces indicate wind slabs will be nearby. Photo: Dallas Glass

  • Storm Slabs

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

    Although we're only expecting 3-6" of storm snow by the end of the day on Sunday. This amount of storm snow wouldn't generally generate a slab in its own right, but the warming trend and denser snow will be more cohesive and prone to propagate across a slope. Most avalanches are expected to fail on a potentially touchy interface following partial clearing Saturday night and could entrain some colder snow. Surface crusts on W-S-E aspects prior to the storm could also permit slabs to break more widely than you expect.  Take advantage of small-scale steep slopes and rollovers to try to get a slab to break. If you're finding reactive snow, stick to slopes less than 35 degrees and avoid large or high-consequence open slopes. 

    A layer of patchy surface hoar at the 3/2 interface has been confirmed on isolated open slopes below treeline. A natural avalanche occurred on this layer on 3/8. Now, the interface has 3 ft or more of snow on and might be pushing the very large size range. While the odds of triggering such an avalanche are low, it remains a wise choice to stick to less consequential terrain on Sunday.

     

    (3/8/2023)

    This natural avalanche occured Wednesday on a North aspect @ 5400 ft in the Bennet Pass area. Crown depths ranged from 1-2' deep. 

    Photo: Trevor Wright

Avalanche Discussion

Cornices are very sensitive right now and have surprised people traveling along ridgelines in recent days. Give these car-sized cantilevers the space they deserve as they may break back farther than you expect.

An excellent observation from Bennett Pass on Saturday found a right side up snowpack with a crust about 50 inches down and reminds us that the days of snow stacking up with limited slab formation have come to an end. This transition to more typical temperatures can produce more reactive conditions than you expect and deserves extra caution as you assess the snow and your terrain selection. Partial sunshine on Saturday will have formed surface crusts on steep W-S-E aspects by Sunday. Despite the recent snowpack consolidation, incidents involving deep snow and disorientation keep Snow Immersion Suffocation and Treewell Safety on our minds. Always travel with and maintain visual contact with a partner.

It's worth a dig in the snow to evaluate the new snow and wind slabs as they form on Sunday, but while you're at it you might as well dig to the 3/2 interface.  On Wednesday observers reported a widely propagating natural avalanche that broke 1-2 feet deep (N aspect, 5400 ft) and we suspect it failed on weak snow grains or surface hoar.  With 51" of snow accumulating atop this interface and counting, it may be down around 3 ft on Friday and you're most likely to find it in sheltered, open slopes below treeline. Persistent grains don't heal quickly and become more reactive during and after a loading event (such as our incoming storm). While it may help you identify a thin gray line (surface hoar) in the upper snowpack you would be wise to keep your terrain selection simple and slope angle moderate given the uncertainty surrounding this layer.

If you get out into the mountains, let us know what you see by submitting a public observation.

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