Avalanche forecast

Mt Hood

Northwest Avalanche Center
View on map

Avalanche danger

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Out of date — this forecast expired 2 years ago.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

Highlights

Tuesday will be a very dangerous and dynamic day in the mountains.  Natural avalanches could run to valley flats at peak instability while large wet or dry avalanches will be easy to trigger on any open slope steeper than 35 degrees.  Keep it simple and limit exposure to all avalanche terrain until this "atmospheric river" passes.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    3

    Prior to the main course arriving Monday night through Tuesday, there was already 3 ft of dry snow above the 12/7 crust and we're looking at another 1.6" of water equivalent through the end of the day on Tuesday.  At middle and upper elevations, much of this precipitation will arrive as increasingly dense snowfall before a potential changeover to rain.  This heavy-loading event in its own right will create widespread instability. As generally S winds increase throughout the day, slabs may become very large in wind loaded areas with the potential to run to valley flats. Dry or wet snow entrainment of snow above the 12/7 crust will help these avalanches gain momentum. Slabs will grow in depth, extent, and reactivity until the snow to rain changeover which will occur at different times at different elevations. Because we have unusually high uncertainty in the timing of peak instability, don't assume you are safe crossing terrain connected to large avalanche start zones while the storm rages on. That includes valley bottoms.

    (12/16/2024)

    Debris from a large wind slab avalanche in the upper White River Drainage on an ENE aspect, 8000 ft start zone.

    Photo: Northwest Avalanche Center

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    The snow line will rise throughout the day. We expect some natural wet loose avalanche activity as snow changes to rain, but we're not sure how easily the snow will destabilize. Don't expose yourself to find out! Even after the changeover to rain, human-triggered wet avalanches will be easy to trigger on open slopes steeper than 35 degrees.

    Example: Large wet snow avalanche.

    Photo: Mt Hood Meadows Patrol

Avalanche Discussion

In times of rapid change to the snowpack, control what you have control over: your terrain selection. Keep it simple and avoid slopes steeper than 35 degrees and stay well away from larger avalanche paths, including those that may be on valley flats.

The fresh, large wind slab in the upper White River drainage and an estimated size 2.5 natural avalanche reported by USGS on the slopes of Mt St Helens may be a harbinger of a more extensive large (or even very large) natural avalanche cycle playing out over the next 24-36 hours.

Sunday and Monday, Mt Hood Meadows Pro Patrol reported triggering large and small avalanches with good propagation in wind-drifted terrain. On Sunday, found these hard wind slabs (P hard) breaking 3-3.5 ft deep on a softer layer of storm snow.  We also heard two reports of avalanches on Mt Adams, one human-triggered and one natural. Both were around 8000ft on S to E aspects in wind-loaded terrain. These recent avalanches are a good reminder that these incremental storms are now building thick unstable slabs across the terrain, and it’s a good reason to step it back until the storm is wrapped up. 

Cornices are now large and as they build increasingly unstable, they may trigger slab or wet loose avalanches on the slopes below.  It is worth considering cornices in the context of the overlapping wet and dry snow problems that will already be challenging to manage in their own right.

Mt Hood picked up another 8-10" of snowfall in the last 24 hours (with 0.8-0.9" water equivalent). Snow levels have been around 4000 ft. Deep snow exists above 4500 ft in the Mt Hood zone, so lower elevation slopes are in play as this storm impacts the region.

We're expecting another 1.6" of snow water equivalent over the next 24 hours. The precipitation Monday night arrives mostly as snowfall, with subtle warming. The heaviest precipitation arrives on Tuesday with a sharp warming trend. The timing of the most significant warm-up, peak precipitation rates, and how rapidly winds increase as the day progresses will dictate when slab and wet loose avalanche activity peak.  

Leading up to this storm, we had a variety of surfaces across the terrain. Solar aspects ( SW-SE) consisted of scoured surfaces and a stout sun crust. Shaded aspects held old wind-drifted snow, some weakening surfaces, and even some isolated surface hoar. The big question moving forward will be how the new load of snow bonds to these, in some cases, weak surfaces. The best strategy during this loading event is to err on the side of caution by giving larger slopes some time to adjust to the new load and continue to gather more information.

Regions covered