Avalanche forecast

Mt Hood

Northwest Avalanche Center
View on map

Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Recent reports confirm that you can trigger a widely propagating and large slab in any elevation band. A layered upper snowpack continues to produce human-triggered avalanches, demanding careful route-finding to avoid wind-drifted snow on slopes steeper than 35 degrees. Wet to dry snow transitions and increasing drift size encourage you to dial back your terrain selection as you ascend. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    A similar weather pattern keeps repeating, but as the snow keeps piling up, it becomes more likely that an avalanche you trigger will be large and more dangerous. Weaknesses within the upper snowpack maintain our concern as the keeps stacking up. Ascending backcountry travelers triggered a large avalanche from below on a previously used uptrack on Saturday - a slightly wind-loaded NW aspect at 5600 ft (below treeline). The details of the avalanche and wide propagation make us suspect that this wind-drifted snow probably overlies previously identified weak snow layers now 10-15" below the snow surface. These sorts of avalanches are much more likely to occur where winds have rapidly loaded the snowpack, but we can't rule out such an avalanche in wind-sheltered terrain. The snow has remained cold with significant wind transport near and above treeline. We don't have recent backcountry observations from these elevation bands, so you may have to assess where the drifts start becoming larger, thicker and more widespread. As a rule of thumb, if you're finding areas of wind-drifted snow more than 1.5 ft deep above the crust, you can trigger a large avalanche and you should stick to slopes less than 35 degrees. At elevations where slabs are less thick and the snow more consolidated, you can navigate around wind-loaded pockets below ridgelines and fresh, sharp, and unstable cornices. Pay attention for signs of unstable snow including whumphs, collapses, or propagating cracks and dial back your terrain selection accordingly.

    (1/7/2023)

    A large avalanche triggered from the Gunsight ridge uptrack. Potential failure on surface hoar or near surface facets and likely ran on the 12/31 crust. NW aspect, 5600 ft.

    Photo: Tosh Forrence

Avalanche Discussion

Saturday was very wet at low elevations where the snow remains wet, shallow and consolidated below the 4500 ft rain/snow line. Ascending higher, winds transported snow in the upper below treeline elevation bands, particularly where NWAC forecast Joe Dellaporta traveled. You can see video footage of intense wind transport at 5000 ft in the Tilly Jane burn scar. The winds were transporting 4-6" of fresh, dense snowfall. While these slabs were reactive at 5000 ft, they will heal quickly due to the mild temperatures. It's at slightly higher elevations that larger slabs will persist.

We're continuing to hone in our understanding of a complex upper snowpack in the Mt. Hood backcountry. In the thicker snowpacks on the south side of Mt. Hood, we suspect you'll find buried surface hoar (somewhat rounding) around 10-15 ft down. The Gunsight Ridge observations leads us to believe that this layer could be found in wind-sheltered terrain on a variety of aspects.  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.

We've received multiple reports of human-triggered avalanches at Mt. Hood since Wednesday, including several more widely propagating avalanches triggered from below in very different elevation bands. Several propagating extended column tests on weaknesses above and below the 12/30 crust raise the level of uncertainty as more rounds of snow and wind maintain the danger at Mt. Hood. As the snow over the weak layers grows thicker, consider the consequences of an avalanche that you trigger increase and so should your terrain selection.

 

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!

Regions covered