Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Although the avalanche danger dropped more rapidly than expected after the last storm, it will ramp up quickly at upper elevations on Wednesday. You can trigger a slab anywhere you find 6" or more of snow above a crust. Blowing snow will be the most obvious sign to avoid wind-loaded slopes steeper than 35 degrees.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The next round of snow and wind will build reactive wind slabs through Wednesday. Moderate to strong ridgeline winds will blow  6" of new snow falling by the end of the day with day to form slabs that could become large at higher elevations. Since slabs will be building on top of a breakable crust formed Monday night, it should be easy to identify the depth of the new wind-loaded snow. Once you start seeing actively wind-transported snow or signs of recent transport, start scoping small potentially wind-loaded drifts before entering more exposed terrain features. Once the drifts are 6" or deeper, you can trigger a wind slab avalanche. If you head above treeline, you should expect to avoid all wind-loaded terrain steeper than 35 degrees where large human-triggered avalanches could become widespread by the end of the day.

    Example: Wind-affected snow surfaces can help identify areas of wind slab. In this photo, the wind was blowing from right to left. In the surrounding area terrain on the right was rocky and wind-scoured and terrain on the left was smooth with no texture (a slab).

    Photo: Lee Lazzara

Avalanche Discussion

A conveyor of heavy precipitation unloaded on Mt. Hood since temperatures turned colder Saturday night. NWAC professionals on Monday found 30" of snow accumulated above the 0.25-0.5" thick 12/18 crust at 5500 ft. The snowfall ended warm and created an upside-down layering in the top 12" of the snowpack. You can read the full report here. Natural and human-triggered avalanches were observed in all elevation bands, painting the picture of a widespread avalanche cycle that peaked on Monday. Rainfall likely reduced snow accumulation significantly below 4500-5000 ft and warming at the tail end of the storm refroze very wet snow to form a crust up to 7800 ft on Monday night. Tuesday was dry and mild with above-freezing temperatures observed at all NWAC weather stations on Mt. Hood.

At this time we don't expect significant avalanche concerns beneath the surface crust that should be buried Tuesday night. However, notable natural avalanches documented on the Clarke Headwall and other high elevation locations provide a good reminder that conditions may be significantly more hazardous above NWAC forecast terrain where this crust may not be present.

While the new snow has been filling in the terrain, you may still find brushy vegetation and open creeks at lower elevations.

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