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

Sustained winds and snowfall will increase the risk of triggering a large avalanche as the day progresses on Sunday, but also as you ascend in the terrain.  Old firm slabs could be difficult to escape if triggered and may underly fresh deposits. Storm snow may become reactive on all slopes steeper than 35 degrees in sheltered terrain.

Avalanche problems

  • Wind Slabs

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

    8-12" of new snow should improve riding conditions, but it will also increase the hazard as sustained SW and WSW winds heavily redistribute it in exposed terrain. These slabs overly firm older wind deposits, sastrugi, and thin crusts on sun-affected aspects. The older slabs will be stubborn, but could still could release unexpectedly. They may exist well down on mid-slope features, and on lower canyon or moraine walls. Softer fresh wind slabs will be easier to trigger and more predictable. Wind-loaded test slopes can be a great place to investigate these deposits, but don't put too much weight on a single observation. Stick to smaller features, wind-sheltered slopes, and areas without signs of heavily wind-affected or punchy layering. Steer clear of steep wind-loaded open slopes at middle and upper elevations. 

    Example: Dense, wind-drifted snow is often just below ridgeline. 

    Photo: Joe Dellaporta

  • Storm Slabs

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

    Storm slabs will become reactive once 8" of snow falls above the previously described old interface. Reactivity could exist on the new/old interface or within storm layers. Expect an increase in the potential for slab failures during or shortly after periods of heavier snowfall. Milder temperatures could limit this problem below 5000 ft, so we expect that sheltered steep open slopes between 5000-6500 ft will be where this problem lurks. 

    Fluctuating freezing levels could also produce wet loose avalanche activity at lower elevations. Avoid steep slopes if rain is falling on snow. Conversely, freezing rain could limit slab development if it occurs.

    (12/25/2021)

    Storm slab propagation in wind-stiffened snow, something you may encounter.

    Photo: Ron Martin

Avalanche Discussion

It has been a wild week of weather on Mt Hood and more is in store. Temperatures have returned closer to PNW norms, so plan bring back your goretex and prepare for a chance of rain if snow levels bump up higher than forecast.

An observer in Mitchell Creek on Saturday found wind slabs on a variety of aspects and somewhat surprisingly, more reactivity on W aspects. This suggests that low-level E winds have been complicating the wind loading patterns in some areas, so you'll need to pay attention and adjust your mental picture of these patterns as you move through the terrain. Lots of recent low density snow has created conditions for Snow Immersion Suffocation (SIS). This may begin to abate as temperatures moderate, but maintain visual contact with your partner, particularly in the trees. Meanwhile, Mt Hood Meadows Pro Patrol triggered isolated large slabs on steep upper-elevation N aspects and small slabs at middle elevations.

Strong to extreme W and WNW winds on Friday redistributed around a foot of snow that fell Thursday night.  Thursday featured a different wind event, but from the E-SE. You might still see some evidence of cornices on atypical aspects from that wind event around the landscape.

The January Drought Layer (JDL)  has been a prominent upper snowpack marker and a popular topic of conservation in our backcountry community these past weeks. You can dig down 2-4 ft and find this weak, sugary snow in most locations around Mt Hood. However, we have typically found it to be weakest on N-E aspects at lower and middle elevations. While we haven't seen any confirmed avalanches on it, it is worth tracking, especially if you head into more data-sparse areas like the north side of Mt Hood or further east near Lookout Mountain. Across the Columbia River and in the West and East South zones, we have seen propagating test scores, whumpfs, and a few avalanches. On 2/15, an NWAC forecaster experienced such a whumphing collapse underneath wind-affected snow in the Mt Adams area. 

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