Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

Your largest avalanche concerns are on steep, wind-loaded slopes near and above treeline. We just received a lot of snow throughout the zone, and avalanches could break several feet deep, resulting in large, destructive slides. Steer around steep, wind-loaded terrain, or any other locations where you see obvious clues like recent avalanches or if you experience long, shooting cracks or whumphs during your travels. 

Problemi valanghivi

  • Wind Slabs

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

    A day out from this large storm, the place where you're most likely to trigger an avalanche is on a wind slab.  You're most likely to find wind-loaded features near and above treeline. The storm layer itself is several feet thick, especially as you go higher in elevation. However, subtle changes by the wind in the top couple feet of snow likely formed reactive pockets and are what will get you into trouble during your outing. These layer you could trigger an avalanche on may only be 1-2ft deep, but there's a small chance they could run deeper. Pay attention to clues such as textured snow surfaces or wind-sculpted features. Feel for heavier snow beneath you. If you find any of these characteristics, or identify any other obvious clues of instability, steer around slopes greater than 35 degrees. 

    Example: Wind slabs and slab avalanches under corniced features. Note the wind-textured snow nearby and cornices above the slope to help you identify which slopes to avoid.

    Photo: Ryan Matz

  • Loose Dry

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

    We received a lot of snow in the last 2 days. The top foot or more is cold, low-density powder. Temperatures will stay cool and this top layer could sluff, or loose avalanche, easily on steep slopes. Sluffs could occur naturally, or you could trigger one if you venture out onto a steep slope. The sliding layers will may only entrain the top few inches of snow, but they could travel up to a foot deep, becoming slightly larger and more destructive.  This type of avalanche tends to be more predictable, but be sure to pay attention to one if you're in steep terrain so it doesn't take you out from behind, or hit a partner. 

    There's the slightest chance that the sun could poke out, and if it does be aware of a subtle shift to some small wetter loose avalanches, although this is not expected. 

    A dry loose avalanche like what you might encounter on Wednesday. They could also be larger. 

Avalanche Discussion

AVALANCHE ACCIDENT COLCHUCK PK, EAST CENTRAL ZONE

We’ve received preliminary information of an avalanche incident on Colchuck Peak, SW of Leavenworth, WA. (East Central Zone) The accident occurred on Sunday, February 19 and involved a group of 6 backcountry travelers. Three members of the group are suspected to have been buried and perished in the event. Another sustained injuries and was evacuated by SAR.  Rescue efforts are ongoing. NWAC is working with Chelan County Sheriff’s office and will make updates as more information becomes available.

Forecast Discussion:

Weather stations in the West Central Zones suggest that we received about 4-6 feet of snow at upper elevations since Sunday morning. Much of this started as heavy, damp snow or rain below about 4000ft before transitioning to snow. The last large burst Monday night delivered about a foot of low-density powder.  The neighboring West North zone reported numerous large natural avalanches which occurred during the storm, and human-triggered small and large avalanches on Tuesday. We expect similar or more reactive conditions occurred in the West Central zone, which received more snow than any other zones. An observer traveled below treeline, up to almost 4000ft on the north side of the Mountain Loop Highway on Tuesday. She found dry snow, increasing in hardness in the top 2ft of the snowpack, before it became moist. At these lower elevations, where not as much wind impacted the area, slab avalanches seem to not be as much of a concern as loose snow avalanche problems. Keep in mind that even if any type of avalanche is small, if a terrain trap is below you it could be deadly. 

An avalanche of particular interest occurred early Tuesday morning in the West North zone. It was a large (D2.5), and occurred naturally as the storm was winding down early Tuesday morning. The avalanche likely originated on a ridgeline at about 5400ft, and traveled through a tight gully down to a road 4000ft below. This brings up a good point that even if you're traveling at lower elevations where little or no snow is present, large avalanches can travel from far above, usually during or just after storm cycles, hitting trails or roads far below and potentially causing serious damage. This is a situation that could occur on many roads and trails in the West Central zone, and likely did during this last storm. If you are out and see a slide, please take a photo and send us an OBSERVATION. 

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