Bollettino valanghe

West Slopes North

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Strong solar radiation will cause wet loose avalanches on sunny slopes. Monitor changing conditions throughout the day and move to shaded or lower-angled terrain when snow surfaces become wet and weak. Stay alert as you climb into upper elevation terrain where you can still trigger a large avalanche in wind drifted snow on slopes 35 degrees and steeper.

Problemi valanghivi

  • Loose Wet

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

    The strong April sun will weaken cold, dry snow surfaces throughout the day and create wet loose avalanches on steep sun-exposed slopes. Sunday will likely be the first day of a prolonged cycle of wet loose avalanches during the upcoming week. The day will start out cold and clear, but dry snow on trees and cliffs will quickly begin to melt and shed. Falling snow on slopes below may be first to initiate loose wet avalanches. The sun will work around the compass as the day progresses, and wet loose avalanches could occur on any steep slopes in direct sun. Uncertainty exists as to whether we will see wet loose avalanches gain mass and grow large, or if sunny slopes will just produce many roller balls and pinwheels. We are erring on the conservative side for Sunday, but whether it's tomorrow, or during the next few days of continued sunny weather, expect to see widespread wet loose avalanche activity.

    Pay attention to rapid changes in the snow surface, rollerballs, and avalanches on similar slopes. It's time to move to shady slopes or head home early when you start noticing these indicators. Keep your return routes in mind as well - slopes you crossed safely early in the day may become wet, weak, and dangerous by afternoon. 

    Example photo of loose wet avalanches crossing common travel routes on the south side of Table Mountain.

  • Wind Slabs

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

    The storm Friday night delivered 1ft of new snow with strong and gusty westerly winds. Observers reported significant wind loading in alpine terrain, while cold low-density powder was less disturbed near and below treeline. Expect wind slabs to become stiffer and easier to trigger as you gain elevation and transition into wind-affected terrain. Thicker slabs of wind drifted snow that formed earlier in the week may still be reactive to human triggers and could be hidden under more recent snow. Avalanches in wind drifted snow could be just a few inches to several feet deep, breaking within recent storm snow or as deep as the crust buried on April 7th. Gather information as you travel and ease into terrain slowly. Use test slopes and hand pits to assess how recent snow is bonding to old snow surfaces looking for sudden or easy failures. Recent avalanches, cracking, and collapsing are clear signs of unstable snow and should direct you to lower-angle terrain. 

    (4/10/2021) A small skier triggered wind slab (D1) on the east aspect of Mt. Herman near 4500ft. The avalanche broke 12in deep. Photo: Pete Durr, USFS Backcountry Ranger

Avalanche Discussion

The back and forth between winter and spring continues to bring spikes in avalanche danger and rapid change. Plenty of cold dry snow from recent storms will thaw on Sunday bringing dynamic conditions. Expect a mix of wet and dry snow problems and big variations between aspects, elevations, and time of day.

Observers in the Baker Backcountry on Saturday reported a handful of small human-triggered and natural avalanches in wind-loaded upper elevation terrain breaking 1-2ft deep. Sun breaks late in the day caused a few rollerballs, but the wet loose cycle has yet to begin. Several near misses occurred over the past week throughout the region including catch and carries in upper elevation terrain and close encounters with large natural glide avalanches. Fortunately, there were no full burials or injuries. 

Continue to identify and avoid cornices. They grew large throughout the winter and will be tested by sun and warming on Sunday. Stand far back from these features along ridges, and avoid travel on slopes below. Plenty of glide avalanches occurred over the past week as well. Keep your eyes peeled for crevasse-like cracks in the snowpack and avoid travel on or below slopes where they exist.

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.

Regioni coperte