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

Sunday won't be an easy day to navigate slab hazard on Mt Hood. Avoid wind-loaded slopes 35 degrees and steeper where drifts will be large and reactive. Near and below treeline, slopes 35 and steeper will become reactive with 6-8" of snow that may lie on a weaker interface or slick crust.

Avalanche problems

  • Wind Slabs

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

    We're back in a more typical pattern for Mt. Hood with moderate to strong SW and W winds accompanied by 8-12" of new snow. Winds and snowfall peak in the early morning hours with blizzard-like conditions, so you may find the most reactive slabs to start the day, but they will remain easy to trigger. Slabs will become large and more difficult to navigate by the afternoon.  Typical tools you use to evaluate slab reactivity may not give you a full picture of the new/old interface where storm snow sits on weak snow or crusts. In this situation, it's more critical to use the terrain to your advantage and avoid all wind-loaded slopes steeper than 35 degrees. Active wind loading onto a slope could lead to isolated natural avalanches and easily human-triggered avalanches.

    Example: Propagating cracks on a reactive wind slab.

    Photo: Will Govus

  • Storm Slabs

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

    We're expecting 8-12" of new snow by Sunday evening. Typically, it takes around 8" of snow with high precipitation rates for several hours to get storm slab instabilities. You might find it only takes 4-6" of new snow to form slabs on colder, shaded aspects that held weaker snow prior to the storm. On aspects with a surface crust prior to the storm, slabs or dry loose avalanches may run fast and far. Typical tools you use to evaluate slab reactivity may not give you a full picture and should not be relied upon. Steer around open slopes steeper than 35 degrees and recreate safely in the trees. 

     

Avalanche Discussion

Reactive simple slope tests may confirm the problem, but an unreactive test shouldn't lure you onto steep, open slopes. Red flags including recent avalanche activity, whumphs, propagating cracks, or cleanly shearing interfaces all point to the problem. If these are present below treeline, the danger may be higher than forecast.

Faceting snow and 1-5 mm surface hoar was widespread prior to the storm. Strong winds may knock down the surface hoar in exposed areas, but it may remain in more wind-protected areas. Sun and above-freezing temperatures to 6500 ft on Saturday should replace persistent grains with crusts on SW-S-SE aspects.  While a typical storm arrives warm and bonds well to pre-existing surfaces, the cold storm arriving Saturday night may not. Colder shaded aspects and wind protected areas may be most dangerous, but a poor bond to the new crust could create fast-running avalanches.

An E and NE wind event 2/23-2/24 redistributed 26-30 inches or more of low-density snow that buried and well bonded to 1-2 cm thick 2/20 crust, with snow continuing through early 2/23. You can find images from this event in the gallery. We're primarily focused on avalanche activity above the 2/20 crust. 

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

 

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