Avalanche forecast

Mt Hood

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Wind slabs linger well above treeline and you can still trigger them. There exists a low likelihood, but high consequence possibility of a very large avalanche descending avalanche paths from the upper mountain. Limit your time in valley flats connected to this terrain.

Avalanche problems

  • Wind Slabs

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

    Elevations above 7000 ft may have more than 6" of dry snow that sits on top of a refreezing crust while lower elevations have moist snow that should refreeze gradually into a crust. Cooling temperatures and continued lighter precipitation Wednesday night will add shallow new snow that may sit on moister snowfall from 3/2. Although winds have been decreasing, there's still enough to drift snow at these wind-exposed elevations. Look for wind-scoured terrain features and sharp wind lips on ridgelines to direct your wind slabs concerns and steer around steep wind-loaded avalanche start zones. Wind slabs at some elevations may entrain recent moist snow to form slides running farther than you expect.

    A very large avalanche (D3) naturally released from the upper slopes of Mt. Hood around 2/28 and serves as a reminder of the very different snowpack / heavy wind loading patterns during the recent storm cycle. These slabs will take more time to heal and may still be very reactive to human trigger. Make very conservative terrain choices if you ascend to the upper mountain and consider the low probability, but high consequence risk of a cornice fall triggering another very large avalanche running well into below treeline elevations. Don't linger in these potential slide paths which may extend several miles into flat valley bottoms.

    Example: Wind slab avalanche triggered within firm wind-compacted snow layers.

    Photo: Photo: NWAC Public Obs

  • Loose Wet

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

    While wet avalanches were quite reactive on Wednesday within recent snow running on the dry/wet snow interface, cooling temperatures should limit the problem above treeline. Near treeline, refreezing crusts may not form fast enough to negate the problem. If you are able to get a wet avalanche moving, it will entrain shallow snow to form avalanches up to size 1.5 and could run fast and far. Below treeline, we think the wet avalanche concern may be limited, but if you can sink your boot in up to your pant cuff, you can trigger an avalanche on a steep slope. Terrain traps such as valley bottoms, cliffs, or recently exposed talus will all increase the risk of even a small avalanche.

Avalanche Discussion

 

Since Sunday morning, a significant atmospheric river brought more than 4" of precipitation to Mt. Hood. 3-4" of wet snow transitioned quickly to rain.  Snow levels fluctuated in the 6500-8000 feet range Monday through Tuesday.  A gradual transition back to snow started occurring Tuesday night at mid-mountain elevations. NWAC forecaster Andrew Kiefer traveled up Pea Gravel Ridge in the wet weather on Wednesday. He found rain changing to snow around 5000 ft with 5" of moist snow above 5000 ft. The moist snow was sensitive to human trigger as wet avalanches that entrained all the recent snow above the March 2nd interface with fully saturated wet snow below. The avalanches gained momentum required conservative terrain choices to navigate above treeline. A snow profile from 6200 ft on Pea Gravel Ridge clearly illustrates the 5" of new snow sitting above a thick layer of wet snow. The 2/19 crust and valentine's crust are also clearly defined in the snowpack. At this time, our primary concern involves the new snow with the rest of the snowpack showing strength.

Remember that all this water descends into creeks, which may have high volumes; snow bridges may be few and far between and may impact your route. Low snow remains an issue in some areas: S and W aspects that melted out in early February may have melted out once again.

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