Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
5 · Molto forte
Limite del bosco
5 · Molto forte
Sotto il limite
5 · Molto forte
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In sintesi

Heavy snow, strong winds, and warming temperatures will create extremely dangerous avalanche conditions Sunday night through Monday. Avalanches will run at all elevations, could be very deep and destructive, and could break trees. Avoid going into, near or underneath anywhere an avalanche could start, run and stop while a significant avalanche cycle is underway. 

Problemi valanghivi

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    3–4

    The deep slab appears to be waking up. We have observations of a couple recent deep slab avalanches that likely ran on the mid-January crust, and were from 4-8' deep. On Saturday afternoon a very large avalanche appeared to have been ski triggered west of Skyline in steep SW facing terrain. Warming temperatures and very heavy snowfall may overload this layer in a widespread fashion overnight Sunday into Monday. As evidenced by this recent slide, and propagation tests at 4,000ft, deep slabs can occur even well below treeline. Avalanches could run into valley bottoms and mature timber becoming very destructive. Stay off of, and well out from underneath avalanche terrain and runout zones Sunday night through Monday. 

    (2/20/2021) This very large deep slab avalanche occurred in the afternoon on Saturday. It appeared to be triggered by a skier but details are unknown. Crown estimated at 4-5' deep.

  • Storm Slabs

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

    Two to three feet of heavy dense snow is rapidly accumulating over lighter, lower density cold snow from the past month. More new snow will fall, and temperatures will continue to slowly rise through Monday afternoon. Storm slabs will run naturally and could be very large. These won't' be your light and fluffy kind, they will be thick and dense. Very strong winds will blow, creating thicker and more reactive slabs in any exposed, open slopes. Storm slabs could step down to become unsurvivable deep slab avalanches, and run to valley bottoms. Stay off of, and out from underneath avalanche terrain and avalanche runout zones.

    Example storm slab avalanche.

  • Loose Wet

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

    Rain on snow, or wet snow on dry snow will continue to cause wet loose avalanches. These could grow to become large on steep slopes. Wet slab avalanches aren't out of the question either, and may become very large and destructive. Wet slides could run over common hiking trails and snowmobile trails in the zone. Stay off of, and out from underneath any steep slopes Sunday night through Monday. 

    Example large, wet loose avalanche.

Avalanche Discussion

The brunt of the atmospheric river comes overnight Sunday into Monday with slowly warming temperatures, very strong wind, and heavy rain/snow to the area. As I write this, 87 inches of cold snow has fallen at the Brooks station on Steven’s Pass since February 12. Much more is on the way, only this time it will be in the form of heavy, dense snow. We haven't seen rain above 3,500ft or so since mid-January, so one of the main concerns is that slabs 5-10' feet thick may begin to come crashing down. The avalanche cycle(s) may last through the day Monday. Saturday's ski-triggered deep slab avalanche may be a precursor to more very large avalanches. In any case, very large storm slabs and wet loose avalanches are expected to continue to run from steep slopes through Monday as our once beautiful cold, dry snow becomes overloaded by wet, heavy rain and snow. During Extreme danger, we may see avalanches occur in areas where they don't often happen. Stay off of, and out from underneath avalanche terrain. Slides may run to valley bottoms, and fill up runout zones. Be careful of roof avalanches on Monday, snow will begin sliding off buildings with the warmup.

WSDOT reported triggering a D3 with control early in the morning on Sunday, in an avalanche path that has only run three times in the past ten years. Professionals noted a widespread cycle of storm and wet snow avalanches to D2 off Lichtenberg, and one appeared to have stepped down to over 5ft deep. Others reported very touchy conditions with storm slab avalanches at Grace Lakes. Back on the 16th, a widespread storm slab avalanche cycle occurred, ranging in size from D1-D2.5. One of these was a deep and very wide avalanche on the South Face of Mount McCausland (See photo below). 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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