Avalanche forecast

Mt Hood

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

You can trigger a dangerous slab avalanche anywhere winds have drifted snow onto a slope 35 degrees or steeper. Anticipate wind-drifted areas or probe for upside-down snow sitting on an older, firm interface. Wind slabs may extend to ridges below treeline as snow levels lower with the storm.

Avalanche problems

  • Wind Slabs

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

    A more vigorous round of moisture arrives with 0.75" of water equivalent (6-8" of snow) piling up above 5000 ft on Mt. Hood in the next 24 hours. Moderate SSW winds will build new fresh slabs that will be large, widespread, and reactive at upper elevations. Focus on the snow and wind transport starting Friday evening as older slabs on a variety of aspects likely lost most reactivity. SSW winds sometimes underproduce on the south side of Mt. Hood but winds could be ripping on the opposite side of the mountain. Assess the average snow depth along with the amount of active and recent snow loading. Fresh cornices may be sharp and extend well beyond the ridges. Avoid all slopes steeper than 35 degrees in the deposition zone. In some cases, slabs could break widely if they step down to weaknesses above and below the 12/30 crust. Near treeline, most slabs will be large enough to take you for a ride. Navigate around more heavily drifted areas. If you find signs of more widespread reactivity such as whumphs, collapses, or shooting cracks, dial back your terrain selection. These could be signs that wind slabs may propagate more widely or step down to weaker snow interfaces.

    Wind slabs may dip down into the upper treeline band between 5000 and 5500 ft as the snow line moves lower. Navigate around wind-loaded pockets near ridgelines in this elevation band. Also, don't rule out the possibility of triggering a 6-12" storm slab if the snow is dense in the morning.

    (1/5/2023) Small shooting crack, undercut by ski track. SW aspect, 6300’. Photo: Ryan Matz

Avalanche Discussion

Reports have been limited from the backcountry on Friday, but Mt. Hood Meadows patrol found isolated large hard slabs above treeline that were sensitive to explosive, but not skier trigger. Wednesday and Thursday we received multiple reports of small wind slabs, storm slabs, and cornice fall avalanches. There was also a large and more widely propagating avalanche on Wednesday, triggered from below. Several propagating extended column tests on weaknesses above and below the 12/30 crust raise the level of uncertainty as we head into a new round of snow and wind loading.

A complex upper snowpack exists in the Mt. Hood backcountry. An inch of snow Thursday night was all that a 4th wave of snow brought to Mt Hood. Below 5000 ft, the warm temperatures will have formed a new crust by Saturday. Joe Dellaporta found a layer of buried surface hoar (somewhat rounding) around 8" down on an E aspect, but not on a similar W aspect on Thursday.  The distribution of this layer remains somewhat uncertain. Several inches below, you may find rounding facets sandwiching the 12/30 pencil hard and inconsistent rain crust that extends up to around 6000 ft. NWAC forecaster Joe Dellaporta found propagation within the layer below the crust in an extended column test (E aspect, 5200 ft), while another observer found easy shears on top of the crust in the Timberline area. At this time, we think the 12/30 facet sandwich may be the more concerning layer since it appears to be present on most aspects and likely extends above treeline. Heed warning signs such as whumphs, collapses, or reactive test results in case the new snow and wind loading stresses these weaknesses.

Although we're not listing cornices as a problem, they should remain on your mind. Cornices have grown over-extended in recent days and some have reached the breaking point. Assume the corniced sides of ridgelines will break farther back than you expect. Cracks near these edges confirm the issue. 

Thanks for all the recent observations! Avalanche forecasting is a community project, so having recent observations from the public is a huge part of the process and helps make for a better forecast.  Keep them coming!

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