Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Morning update: Snow levels around 6000 ft have produced saturated snow into middle elevations. Human-triggered wet loose avalanches are likely at middle elevations. 

Another round of heavy snowfall Saturday night will allow for significant wind loading through Sunday. Reduce your terrain selection, noting the degree of active and recent wind redistribution. Cracking, punchy snow, and sharp cornices all remind you of the problematic steep, lee slopes where you can trigger a large avalanche.

Problemi valanghivi

  • Wind Slabs

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

    Most of the heavy snowfall will occur Saturday night, but moderate to strong winds will continue redistributing snow through Sunday in exposed terrain. Wind slabs maintain the potential to be large and danger at upper elevations where high uncertainty exists. As the storm relents, folks will be tempted to explore these elevations, but be aware that avalanche depths and potential size will increase once we you lose track of the 1/3 crust. The situation at middle elevations remains will be more predictable and generally smaller with less than 1 ft of snow above the 1/3 crust. Slabs could still be large in heavily wind loaded locations, running efficiently on a crust. Once you enter exposed terrain, note the slopes getting scour and sastrugi, then avoid slopes greater than 35 degrees on the opposite side of the ridgeline. Active wind loading, cracking snow, and pillow-like drifts all remind you of the problem. If the storm stays cold and dry enough, wind loading could extend into more exposed terrain at lower elevation, so treat this terrain similarly.

    If you find more than 8" of snow above the crust in wind-sheltered areas, a storm slab could be on the menu. Check the slab and interface for reactivity prior to considering any steep slopes.

    Example: Anticipate where wind slabs lurk by looking for where the snow is depositing.  Cornices are often great indicators of potentially wind loaded terrain beneath. 

    Photo: Joe Dellaporta

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Fluctuating snow levels Saturday night and Sunday brought over an inch of liquid water into the upper snowpack. Below 6000 ft, you're likely to find heavy, dense, and saturated snow along with poor riding conditions. Wet avalanches that entrain recently dry snow will entrain snow above the 1/3 crust. Give the upper snowpack time to drain and steer away from all steep open slopes with more than 6" of saturated snow above the crust (mostly found at middle elevations).

    (12/2/2024)

    Avoid complex terrain in areas where you find yourself sinking into wet snow or see evidence of wet snow avalanches. 

    Photo: Joe Dellaporta

Avalanche Discussion

Increasing snowfall Friday afternoon added 4" of new snow which sits above a firm 1/3 crust at middle elevations (breakable at lower elevations). In the mid-day hours, this snow produced wind slabs up to 3" thick that were not yet hazardous. The crust was formed by the Thursday-Friday storm  which brought 1.5-2" of snow water equivalent by the end of the day on Friday. The storm started with 5" of snow on Thursday, but the rain/snow line rose to around 6200 ft Thursday night. Rain was reported to 6600 ft early Friday, making generally small wet avalanches easy to trigger by Mt Hood Meadows patrol. Temperatures cooled in the early afternoon, bringing snow back down to the ski areas bases, but only a dusting to an inch of snow has accumulated. 

Altough conditions were less hazardous than forecast on Saturday, Mt Hood's avalanche danger can increase quite rapidly as more snow builds and redistributes atop the most recent crust. Go into Sunday with a different mindset, anticipating an increase in danger. The amount of snow above the last crust and the fluctuations in depth over short distances will be your most critical observations. The deeper the recent snow and the more widely varied, the higher the potential for you to trigger a slab.

We don't know how high the 1/3 crust will extend in the terrain on the south side of Mt Hood. This crust may be thinner or non-existent in some terrain on the drier NE side of Mt Hood - we simply don't know.  Widespread surface hoar that formed earlier in the week up to 7000' may make avalanches more likely in some areas.  In the nearby East South zone, we have a confirmed slab above this buried surface hoar layer, justifying a persistent slab problem. Therefore, take heed of any unusual signs of instability, such as long shooting cracks, whumphs, or fresh natural or human triggered avalanches. Any of these signs should have you dialing it way back to slopes less than 30 degrees.  A video in the gallery illustrates the problem in the East South zone. If you don't find a supportable crust in your terrain, you'd be wise to carefully evaluate the snowpack before engaging with larger open slopes or unsupported features, where a more slab failure would put you in harm's way.

The overall snowpack coverage has improved rapidly over the last few weeks, especially compared to last year!  Let us know what you see by submitting a public observation. 

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