Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

A multi-day storm cycle will produce larger and more dangerous avalanches that are primed for human trigger near and below treeline. Very large avalanches may run naturally from above treeline terrain or Mt. Hood's upper mountain. Stay out of large avalanche paths or large open areas in canyon bottoms where avalanches may reach from above.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    Wind slabs likely grew up to very large size above treeline by Sunday and they will be easy to trigger or may release naturally. These avalanches can run down to lower elevation terrain and valley bottoms. Near treeline, wind slabs may be small-large, but should still be widespread. Around 2 ft of lower-density snow was blown around by strong WSW winds with very strong gusts on Saturday. We're expecting around a foot of snow to fall Saturday night through Sunday with moderate to occasionally strong winds. Slabs may run easily on the existing firm surfaces. Give avalanche terrain at upper elevations a wide birth as this storm and avalanche cycle continues.  Avoid large avalanche paths where an avalanche can start, run, or stop. This includes valley bottoms where avalanches may reach from above. Near treeline, stick to smaller terrain features and avoid wind-loaded terrain steeper than 35 degrees.

    Example: Wind Slab avalanche.

  • Storm Slabs

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

    We're one day removed from Saturday's natural avalanche cycle down to very low elevations. 3" slabs of denser snow formed above very-low-density snow. By Sunday, these dense layers will become thicker, capable of producing larger and more dangerous avalanches. With moderate snowfall forecast to continue, human-triggered avalanches are likely and natural avalanches may still be possible, especially during periods of heavier snowfall.  Sunday will be a great day to seek out smaller, lower angled, and treed slopes. Avoid all sheltered slopes steeper than 35 degrees with unsupported convex rollovers harboring the greatest danger. You can use small unsupported test slopes to confirm the problem in your terrain.

    (2/13/2021) Tree-bomb triggered storm slab indicating very unstable snow.

Avalanche Discussion

With around 2 ft of fresh snow in your terrain by Sunday, Snow Immersion and Suffocation remains a significant concern. If you recreate in forested areas, travel with a partner and maintain visual or audio contact. 

Storms have been unrelenting on Mt. Hood for several days now: 10" of snow feel Thursday through Thursday night, another 15.5" fell Friday through Friday night, and over 6" fell during the day on Saturday. The snow was very cold and low-density until On Thursday, as WSW winds increased and low-elevation temperatures increased sharply mid-20's late Saturday morning. This produced a slab of denser snow. Several small natural avalanches were reported by NWAC professionals on Saturday at unusually low elevations (around 5000 ft). WSW winds were strong, but due to limited visibility we lack information about avalanche activity near or above treeline.

Despite a multi-day wind event prior to the recent snowfall, no new avalanches were reported since last week. In some areas, snowfall starting Thursday may have fallen on a thin freezing rain crust.   An observation from Newton Canyon found this surface crust even on NE aspects below 6000 ft. 

The stout mid-January crust is considered the new "ground" with a strong snowpack structure in place below this layer. Weak and faceted snow just above the stout rain crust was responsible for a number of avalanches last week, but no new evidence of avalanches on this interface suggests these facets are gaining strength. This weak layer (which is similar in structure to the fatal avalanche in WA)  still exists around Mt Hood and could produce a very large avalanche, but no evidence of recent avalanches on this layer have been reported.

Headed north to recreate?  We have a tricky snowpack with persistent slab problems in all forecast zones across the state line.  Take the time to read about the different snowpacks that have developed further north and adjust your terrain selection accordingly. 

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Preliminary avalanche incident information Monday February 8th, 2021: Two snow bike riders were caught and buried by a very large avalanche in the mountains west of Salmon la Sac Sno-Park along Cle Elum Lake. One snow biker was partially buried and was able to dig himself out. The other rider was fully buried and killed by the avalanche. The avalanche occurred on a north aspect at 4400 ft in the Knox Creek drainage. This terrain lies in NWAC’s East Central forecast zone. Avalanche classification: HS-AV-R3-D3-O. See the short video in the media gallery below.

All of us at NWAC want to extend our condolences to family, friends and the local community following this tragic event.  

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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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