Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

The warmest temperatures of 2021 will have an impact on the mostly dry upper snowpack at Mt. Hood on Saturday. Pivot away from the sun as the snow becomes sticky and wet, creating the potential for avalanches to entrain snow down to the 3/24 crust and become large. The warm-up creates some uncertainty and if you see signs of larger avalanches, reduce your overhead exposure and dial back your slope angle.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Freezing levels rising to around 10,000 ft will rapidly transition the upper snowpack from dry to wet snow. A low-level temperature inversion held loose wet activity in check at lower elevations while moderate winds above treeline cooled the snow at upper elevations on Friday. We think that all elevations will receive temperatures in the 40s on Saturday and winds will calm down, allowing surface crusts to break down and the top few inches of snow becoming sticky and wet on sun-affected slopes. Once this occurs, expect the recent 8-12" of snow to destabilize, producing rollerballs and loose wet avalanches. While most loose wet avalanches may be small, some could gouge up to a foot deep, running fast and far on the 3/24 crust. Pay attention to your overhead exposure and to slopes 35 degrees and steeper as the sun moves around the dial. At the first sign of rollerballs and avalanche activity, transition to aspects away from direct sunshine. On northerly aspects, lower elevation slopes may warm enough that you can trigger a wet avalanche near and below treeline as the snow moistens. If you find this occurring, dial back your slope angle. 

    Example: (3/23/2021) Numerous natural loose wet avalanches like these were witnessed at Snoqualmie Pass. SE 5000. Snow Lake Divide.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Friday's moderate NW winds following sustained westerly winds up to 45 mph Wednesday through early Thursday, building stubborn hard slabs that you can still trigger. These slabs are more likely to be large on leeward N-E-S aspects, particularly where surface crusts have not formed. You're less likely to find blowing snow actively loading start zones heading into Saturday, so look for signs of recent N through W winds. Pillow-like drifts, fresh cornices, and stiff or textured snow remind you that you could trigger a wind slab in your terrain. Hollow snow means you are on top of a wind slab. If you observe these signs, continue to navigate around start zones and slopes over 35 degrees. 

    Example: Wind slabs forming adjacent to wind-textured snow.

Avalanche Discussion

Wednesday afternoon through Thursday brought 8-12" of snow with strong sustained W winds and extreme gusts Sunday night. Mt. Hood meadows triggered a handful of wind slabs up to size large on Thursday with both ski and explosive triggers. NW winds actively continued to load E and S aspects into the day on Friday.  MHM Pro Patrol triggered several more avalanches with explosives Friday, including a 2-3 ft deep large hard slab on an ENE aspect at 6400 ft. The avalanche failed within the storm snow.  These recent wind slabs sit on a thin melt-freeze crust (3/24) that likely formed on aspects receiving sunshine. Sunday night and Monday brought significant new snow accumulation to Mt. Hood (12-18" at ski area bases). An observer evaluating the snowpack on a NE aspect of Elk Mountain at 5400 ft found moderate reactivity, but no propagation in ECT results on this interface. The weekend's snow sits above another melt-freeze crust formed during warm and sunny weather last week.

Freezing levels rising to near 10,000 ft hasn't occurred in some time. Warm temperatures in the early spring come with some amount of uncertainty. We think that the recent snow will be well settled and primed to absorb any melting snow. However, if you see signs of any unusual large wet slab avalanches, water could be melting down to and lubricating crust interfaces such as 3/24 or deeper. Typically wet slabs require weak snow above the interface and we don't think that meltwater will make it very deep into the snowpack, so wet slabs remain very unlikely. If you observe signs of wet slabs, reduce your exposure to large avalanche slopes around and above you.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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