Avalanche forecast

Mt Hood

Northwest Avalanche Center
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Avalanche danger

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

Dangerous avalanche conditions will develop rapidly with fresh snowfall as winds will be plenty strong for significant snow transport at middle and upper elevations. Thick lens-shaped pillows and textured surfaces may extend onto mid-slope or down-canyon features. Avoid wind-loaded slopes steeper than 35 degrees, and beware of small, sensitive cornices.

Avalanche problems

  • Wind Slabs

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

    Through Sunday, we're getting plenty of wind but limited snowfall (4" on sheltered open slopes). We expect 5-7" of snowfall over the next 24 hours with moderate to strong winds. If this snowfall materializes, it will ratchet up the danger, forming large slabs that may be firm and difficult to escape if you trigger one. Typical trigger locations will include steep avalanche start zones that were just starting to load up on Sunday but will become significantly more hazardous by Monday as the danger becomes more widespread on favored aspects. Winds may also rip down (or up) canyons, scouring some aspects and heavily loading others. Expect slabs to form on mid-slope gullies with likely slab trigger points on steep, convex rollovers. Hazard will likely increase throughout the day as more snow falls, drifting onto lee slopes as soon as it reaches the slopes. Given this scenario, you'll want to monitor the amount of snow above the the 3/8 interface, the rate of snowfall from the sky (check weather station data), and gauge the quantity of blowing snow to assess the danger in your terrain. Use small test slopes to evaluate how easily the wind slabs fail on the 3/8 interface (crusts or old snow), but slabs may also break within more recent snow above the more discernable interface.

    You may also be able to trigger a small avalanche on steep affected slopes at lower elevations. These will be small and easier to steer around where you observe lens-shaped pillows or encounter firm, punchy surface snow.

     

    Example: Wind slab avalanche  on a large open slope.

    Photo: Dallas Glass

Avalanche Discussion

NWAC will be closed on Tuesday, March 12th, as we gather and grieve following the death of one of our forecasters, Matt Primomo. We will not issue regular avalanche or mountain weather forecasts on Tuesday. We will return to normal operations on Wednesday, March 13th. We appreciate the community's understanding and support during this time.

Discussion:  

There is a slight chance that some areas may have buried surface hoar on 3/8. Before the storm cycle, observers found surface hoar on middle and lower-elevation slopes with open canopies. Middle-elevations would be the most likely candidates for surface hoar preservation. Any avalanche failing on such an interface could break widely across terrain features. If you encounter warning signs such as whumphs or shooting cracks, dial back your terrain selection to slopes less than 30 degrees as avalanches.

Cornices are growing and sensitive. Tread cautiously as you approach a ridgeline's edge or ascend on the slopes below. Actively loading cornices may fail without warning, potentially triggering an avalanche on the slopes below.

The weekend featured stormy weather on Mt Hood with about 4" of snow settling onto sheltered open slopes below treeline. Winds redistributed that snow into sensitive cornices pointing to the generally small wind slabs on the slopes below. A warm, spring-like day on Friday saw freezing levels rise to 8000 ft, putting crusts up to these elevations on all but shaded aspects. Observers reported the crust to be supportable and around 0.75" thick on sun-exposed aspects at middle elevations. We expect that the 3/8 crusts exists at least at lower elevations and perhaps into middle elevations on shaded aspects.  Below the crust, the snow increases in density and is gradually rounding, giving us no cause for concern. Therefore, focus on the snow above the 3/8 interface as you travel for stability concerns, using hand pits and small slope tests to evaluate as you move into increasingly wind-exposed areas.

Photos in the gallery depict conditions prior to the storm.

If you're out in the snow, share your observations with us and your local backcountry community.

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