Lawinenlagebericht

Mt Hood

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
4 · Gross
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Very large avalanches could release naturally anytime Monday as 6-8" of recent liquid water at lower elevations translates into massive wind slabs above 7000 ft. Avalanches originating from the upper mountain could run long distances to bury and kill you on flat open areas far below, so avoid all exposure to large avalanche paths. At lower elevations, the snowpack continues to adjust to the water additions, so stick to slopes less than 35 degrees to avoid triggering a Wet Loose avalanche.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    Very heavy wind and snow loading on Mt. Hood's upper mountain over a 48 hour period continues to raise the probability and consequences of very large natural avalanches above 7500 ft and into terrain above 8000 ft for which NWAC doesn't forecast. These avalanches could run thousands of feet, across flat terrain, and into valley bottoms. Travel in areas where avalanches can start, stop, or run is not recommended. Look for terrain where trees are stunted or non-existent to avoid exposure from high above.  With snow levels forecast to rise to 8000 ft Sunday night, dry snow problems will redevelop at the upper reaches of our forecast area on Friday as snow levels lower to around 6500-7000 ft. From 6500-8000 ft expect reactive small to large slab avalanches developing as winds redistribute dense snow. 

    Two very large natural wind slab avalanches observed Friday (details in the discussion below) remind us of the scale of these avalanches (which could be even larger on Sunday). Don't try to nuance these problems and just avoid all avalanche terrain at upper elevations on Monday.

    (12/18/2020) The debris pile of a large (D2.5) natural avalanche that occurred Thursday night at Mt Hood Meadows in closed and uncontrolled NE facing terrain. The avalanche initiated around 6600' on the rain crust formed 12/9.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2

    Six to eight inches of water hit Mt. Hood's slopes in 48 hours ending Monday morning with snow levels fluctuating between 6500-8000 ft. We don't know how well the snowpack is handling this water because visibility was poor on Sunday, but we expect you can find debris from a cycle of natural wet avalanches. We're expecting 0.5-0.75" more rain to fall during the day to maintain the threat for large, deeply gouging and powerful Wet Loose avalanches. If your boot sinks in more than 6", you can trigger a Wet Loose avalanche. We maintain some uncertainty about slopes above 5500 ft to handle the recent water and the potential for water to pool above the 12/9 crust. An avalanche running on this crust could be very large and destructive.  Avoid all avalanche terrain steeper than 35 degrees and stay out from under large avalanche slopes.

    Example: Large loose wet avalanche.

Avalanche Discussion

We're in the final days of a very active weather pattern and we have a lot of uncertainty about how well the snowpack is handling the rain and snow. If you head into the backcountry, you'll need the knowledge to avoid large avalanche paths and a conservative mindset. Small, low-angle, slopes at lower elevations are likely to afford safer travel.

Backcountry observations on Sunday were non-existent, but we do know that several inches of new snow fell down to 6600 ft, creating manky, wet snow that could create avalanches on steep slopes. 6" of water falling by late Sunday had a major impact, causing flooding on groomed ski runs. The impacts on the backcountry snowpack remain to be observed.

Observers on Friday reported shallow wind slabs had formed, but generally good stability below ~6000'. However, several very large natural avalanches released overnight Thursday at Mt Hood Meadows Ski area in closed NE facing terrain between 6300' and 7500'. These avalanches occurred in wind loaded terrain and had crown heights of several feet up to 6+ feet deep. These very large avalanches slid on the firm rain crust formed on 12/9/20. It is likely that they occurred during a period of intense wind transport on Thursday night.

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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