Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 8 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

As the storm cycle continues, wind drifts will be larger, with intense active windloading maintaining the risk of human-triggered and natural avalanches.  Wind-sheltered terrain reduces, but does not eliminate your risk. Deep new snow raises the risk of snow immersion accidents - keep partners in sight and be prepared to respond.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    We're still in the thick of the storm cycle through Thursday. Although the danger rating isn't changing, the likelihood of triggering an unsurvivable avalanche should increase relative to Wednesday. Around a foot of fresh low-density snowfall through Thursday adds fuel to the Mt Hood windslab machine as winds ramp into the strong to extreme range. These firmer wind slabs are likely to overly areas that saw a relative break in the wind and right-side-up snow on Wednesday. This anticipated reactivity would be confirmed by cracking as you walk, punchy layering, or settlement of the underlying low density snow as you move across a slope. If you find this structure, keep it simple and avoid all upper elevation avalanche terrain where avalanches could descend several thousand feet toward valley bottoms. At middle elevations, avoid wind loaded slopes steeper than 35 degrees, including cross-loaded gullies, mid-slope rolls, and down-canyon deposits on the sides of morraines. Expect more subtle, smaller slabs in areas where you find less rock and tree anchoring at lower elevations.

     

    Example: Large wind slabs like these may release naturally or by human trigger on Thursday.

    Photo: Joe Dellaporta

Avalanche Discussion

So far, Mt. Hood has picked up 17–20 inches of snow, with storm totals in the 2-3 ft range by the end of the day Thursday. Deep snow increases your risk of Snow Immersion and Suffociation, particularly around small trees and creeks. Mt. Hood Pro Patrol reported triggered wind slabs up to 18 inches deep, though with less propagation than expected, and no storm slabs observed. Low-density snow was widespread on the surface. Similar conditions were found in developing low-elevation snowpacks (up to 1.5 feet deep) near Clear Lake Butte and Timothy Lake. Storm snow has been bonding well to the underlying crust. 

The lower and middle snowpack remains strong, with primary concern above a prominent 1/3 rain crust. In many areas, you may also encounter a 1/6 sun crust on SW–S–SE aspects, overlain by 6–8 inches of consolidated snow. By Thursday, more than 2 feet of snow is expected above whichever crust is present. Given reports of good bonding, avalanches are most likely to fail within storm snow accumulating since 1/6, although though crust involvement cannot yet be ruled out.

Additional avalanche concerns include growing and potentially sensitive cornices, which could fail unexpectedly and trigger wind slabs on the slopes below. Storm slabs may also develop in less wind-affected terrain, especially during or shortly after periods of 1–2" per hour snowfall rates or with slight afternoon warming. Low density surface snow is susceptible to "sluff" as a dry loose avalanche on slopes approaching 40 degrees. 

By Wednesday, snow was accumulating down to 1,000–1,500 feet, covering previously dry ground. Shallowly buried obstacles remain widespread at lower and middle elevations, increasing consequences in both falls and avalanches.

Images in the gallery show touchy 3–6 inch slabs from early in the storm cycle, as well as pre-storm snowpack conditions.

Regioni coperte