Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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3 · Marcato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

It's time to adjust our mindset and take a step or two back, because avalanche danger is increasing. Dangerous conditions are expected to develop with new snow and warming temperatures on Sunday. Slab avalanches should become most likely and large at upper elevations, where wind has created thicker slabs. A powerful winter storm is expected to create a widespread natural avalanche cycle Sunday night through Monday. 

Problemi valanghivi

  • Storm Slabs

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

    New snow coming in with rising temperatures is not expected to bond well with the current facet/crust surfaces. Look for signs of instability like shooting cracks, and fresh slab avalanches. You can use test slopes or quick hand pits to check how the new snow is reacting. Once about 8" of snow has fallen, expect you could trigger shallow slab avalanches on steep slopes. More snow will accumulate at higher elevations, and combined with some wind drifting these slabs could become large enough to injure or bury you. At lower elevations, warming temperatures and rain to ~3,500ft may create potential for small loose wet avalanches and rollerballs. 

    Lots of weak snow surfaces are expected to get buried by the new snow at all elevations. Storm slabs could become touchy if we receive enough new snow. Theres potential to trigger shallow slabs from the edges of a slope, or from beneath steeper slopes that have been wind loaded. Stay alert during the day, watch your slope angles and stick to lower angled slopes if you are observing signs of instability. Sunday is not a great day to go big or hang it out there, as a much larger, powerful storm is headed towards us Sunday night into Monday. 

    Example storm slab beneath a cliffy area.

    Photo: Mt Hood Meadows Patrol

Avalanche Discussion

The upcoming set of storms will bring a drastic change to our snowpack over the next few days. For Sunday, up to 10" of new snow may fall at the pass. During the day theres potential for a brief lull in the precipitaton ahead of the next, more powerful storm for Sunday night through Monday. With the rise in snow levels the snow could become thicker or moist at lower elevations during the day. Observers have documented a mix of facets and surface hoar over brittle suncrusts, wind stiffened snow, and soft recycled powder. With this in mind, conditions may become reactive in a hurry on Sunday once enough new snow accumulates. The big bang will come Sunday night through Monday, when heavy snow/rain and continued rising temperatures are expected to create a significant and widespread avalanche cycle.

With cooler temperatures and cloud cover on Saturday, surface facets appear to have stayed intact, even on direct south-facing aspects. Beneath the surface, there are a number of crusts and potential weaker layers in the upper 3ft of the snowpack. The Valentines Crust serves as a prominent marker, as it's fairly thick in most places. On northerly aspects, it may be crumbly and mixed with facets, on southerly aspects its a stronger melt-freeze crust. There is about 2-3ft of recent snow over it near the crest, and about 1-2ft over it further east in the zone. 

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