Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

Dangerous conditions are expected to continue on upper elevation terrain- You could trigger large and surprising slab avalanches, especially in areas recently drifted by the wind. Give the new snow time to settle, and remember there's still a chance you could initiate a very large deep slab on shaded slopes. Wet loose avalanches may run naturally on slopes receiving direct sun.

Problemi valanghivi

  • Wind Slabs

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

    Winds transported lots of snow on Tuesday, and observers triggered wind slab avalanches.  Slab avalanches may break within new snow instabilities or further down to the old snow surface formed prior to this storm cycle (sun crusts on previously sunny aspects or weak faceted snow on shady aspects).  If they break deeper, avalanches could be large and surprising. Look for signs of instability like cracking, or whumphing as you travel. Look for signs of wind drifted snow, like surface textures and feel for stiffer snow near wind-exposed areas.

    Give the new snow and wind drifted areas time to heal, traveling on less steep and more supported slopes. Wednesday is a good day to avoid terrain where avalanches within the new snow may overlap with the deep persistent slab problem, such as wind affected NW-NE aspects.

    Example wind slab avalanche

  • Deep Persistent Slabs

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

    The chances of triggering large deep persistent slab avalanches are few, but not impossible. Be especially cautious in areas with a shallow snowpack, such as west and northwest aspects, and parts of the range that are further east or north such as Harts Pass. What can you do to manage this low-likelihood/high consequence problem?   You can limit your exposure to large start zones and very steep slopes, especially those with big overhanging cornices (see photo).  Also, avoid complex and unsupported terrain, shallow, rocky areas, and unsupported slopes (see photo in Drew's ob).  

    (3/10/2022)

    In the center of the photo is a recent D2.5 deep slab, likely triggered by a cornice fall. 

    To the right of the photo, you can see a similar-sized avalanche that likely occurred during the natural cycle of 2/28-3/1.

    McGregor Mtn, NNE, 7,200ft.

    Photo: Matt Primomo

  • Loose Wet

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

    Warmer snow, strong sun, and warming temperatures may set off a round of loose wet avalanches on Wednesday. Observers noted a few natural wet loose slides in Delancey (S facing terrain) on Tuesday, and we expect more to run and in more areas on Wedensday. These slides could pack a punch. Look for wet sticky snow, rollerballs, and fresh fan-shaped avalanches to clue you into this avalanche problem. Avoid large steep slopes, and steer around consequential terrain once you observe these signs. Consider avoidance of traveling on or underneath steep slopes that catch the sun in the middle of the day.

    Example wet loose avalanches

    Photo: Matt Primomo

Avalanche Discussion

Monday and Tuesdays storm dropped nearly an inch of water weight, and increased the overall snowpack depth at Washington Pass by 13".  Observers were finding about 12" of new snow on Tuesday, with higher density snow at lower elevations. Folks reported hearing large natural avalanches in the Hairpin Valley, and observers were able to trigger large (D1.5) wind slabs that ran on the new/old interface at 6,800ft on Kangaroo. Loose slides were easy to trigger on steep slopes, and many small natural loose slides were observed off steep features. Wednesday will be a good day to stay off of steep slopes as the new snow will take time to settle. 

On March 9th observers near Harts Pass remotely triggered a large, R3-D2 avalanche from 20-30 feet away. The avalanche occurred roughly around 6,600ft on a north aspect and failed on facets above a crust.  However,  a crown profile revealed a uniquely shallow snowpack suggesting previous avalanches may have already run on this interface.  On March 3rd, a size D2.5 avalanche was triggered nearby on Tatie Peak on a northeast aspect at 6,800ft. Fortunately, no one was caught in either of these avalanches. Another deep avalanche likely occurred on the late January weak layer with cornice fall around March 8th on McGregor Mtn, NNE, 7000ft. Observers reported other deep crowns in the Hairpin Valley and near Azurite Pass after a widespread avalanche cycle on 2/28-3/1. 

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