Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

We're still in a significant storm cycle, and the potential for very large avalanches remains at upper elevations. You can still safely recreate on slopes less than 35 degrees at lower and middle elevations. Stay off of and out from under wind-loaded slopes and anything connected to upper-elevation start zones.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    Most avalanche activity will be related to new storm snow and wind loading, but uncertainty remains up high as wind slab formation remains unrelenting.  Most slabs at middle and lower elevations will form from snow that falls from Thursday afternoon onwards as snow accumulates over a widespread layer of wind buff and scour. Expect this new snow to be in the 12-15" range with moderate winds in the prime range for slab formation. Slabs should be reactive, easy to trigger on all wind-loaded slopes, and could be large. Active wind loading, shooting cracks, and punchy snow layering are clear signs of instability. Avoid wind loaded lee slopes on Friday.

    It remains highly prudent to stay out from under all avalanche paths connected to upper elevation start zones. Given active wind loading, a very large avalanche could fail without warning and would be unsurvivable; running to valley flats. 

    Example: Shooting crack warning of present instability.

    Photo: Joe Dellaporta

  • Storm Slabs

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

    Storm snow keeps adding up in wind-sheltered terrain.  During periods of rising temperatures and heavier snowfall, the danger will increase, then slowly decrease during relative breaks and cooling trends. Slabs likely overly a layer of consolidated wind-affected snow from 12/25. Slabs could form above this layer and may fail at the interface or with subtle instabilities forming within the storm snow. Use quick shovel shear tests, hand pits, and test slopes to assess the reactivity. Assume slopes 35 degrees and steeper are reactive unless you have strong evidence to the contrary.

    Example: A storm slab triggered by explosives during morning mitigation efforts at the Summit at Snoqualmie on 12/26.

    Photo: Summit at Snoqualmie Pro Patrol

Avalanche Discussion

A major Xmas Day - Boxing Day storm brought 26" of snow to Mt Hood and it's still coming down. Winds were sustained in the 40-50 mph range with gusts over 100 mph that knocked down medium-sized heavily rimed trees 25" in diameter. Not surprisingly, Mt Hood Meadows Pro Patrol found highly reactive snow around 7:30 AM. Storm slabs 8" deep were easy to trigger as 4-12" slabs overburdened lower-density snow that fell before the winds ramped up. By mid-day, the slab reactivity decreased significantly.

Thursday afternoon, lower-density snowfall was falling once again with less wind effect, so a similar story might play out on Friday with new storm and wind slabs overloading this new layer of lower-density snow.  We're expecting 12-15" of snow over the next 24 hours with no breaks between systems to allow for stabilization. WSW and SW winds will be in the productive range for slab formation throughout this snowfall. 

Below 7000 ft, expect 1-3 ft redistributed snow above a well bonded 12/24 crust. Above 7000 ft, the 12/24 crust fades away and the first crust you'll find is the stout solstice crust.  This crust was created following a rain event up to high elevations on December 17th that resulted in a widespread avalanche cycle up to D3.  Photos in the gallery show conditions prior to the recent storm cycle, but avalanches of a similar magnitude will be on the menu once again on Friday.

 

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