Bollettino valanghe

Snoqualmie Pass

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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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

As this storm winds down, be sure to give the snowpack some time to settle before stepping into consequential terrain. Springtime weather including temperature fluctuations and sunshine may delay the healing process longer than you are used to. You should avoid slopes over 35 degrees anywhere you find wet and heavy snow.

Problemi valanghivi

  • Loose Wet

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

    This storm was generally wet and warm, which resulted in rain, mixed precipitation, and heavy wet snow at mid to lower elevations around the pass. On Wednesday, we’re going to add some dynamic springtime weather to the mix, which could help to weaken the recent storm snow even more and increase the likelihood for wet avalanches. Keep an eye on the snow surface as you travel throughout the day to see how the temperature and sunshine are affecting it. You may be able to trigger a wet avalanche on any steep slope over 35 degrees where you find wet and sticky snow deeper than your ankle. These slides can entrain significant snow and grow large enough to bury or kill you as they descend, running far distances on a firm underlying crust. We expect the larger and more dangerous slides to occur above the rain/snow line where recent snow totals are deeper. But even smaller slides will be powerful with snow this heavy, so don’t get caught near terrain traps like gullies or cliffs and be sure not to get pushed into a tree or rocks.

    (3/15/2022) Rain runnels from the onset of precipitation at mid elevations. Avoid slopes over 35 degrees anywhere you find wet and heavy snow. Photo: Andy Harrington

  • Storm Slabs

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

    Be sure to take a look at all of the recent snow delivered by multiple rounds of precipitation and fluctuating freezing levels during this storm. On Tuesday the storm snow was found to be a bit “upside-down” with heavy snow over weaker snow, and you should be targeting a similar set-up on Wednesday. Slabs should be thicker as you ascend in elevation or in wind-loaded terrain and will be easier to trigger on steep features over 35 degrees in these areas. You can use small test slopes or quick hand pits as you travel to get a sense of how the snow is bonding or reacting to your weight. Although we expect these slabs to heal relatively quickly, there is still plenty of uncertainty about their reactivity, specifically at upper elevations. So give the snowpack the time it needs to adjust to the recent load by avoiding those locations where slab avalanches are more likely. 

    (3/15/2022)

    Compression tests highlighted a mid-storm density break and failures above the Early March Crust on 3/15. You can use hand pits and test slopes as you travel to get similar information about slab potential.

    Photo: Andy Harrington

Avalanche Discussion

As of Tuesday afternoon, a series of storms has delivered about 2.5” of water to Snoqualmie Pass since Sunday. Fluctuating freezing levels during the event means that snow, rain, and a mix of precipitation types fell at different points in the near and below treeline bands. On Tuesday, NWAC team members in the Kendall Peak area found up to a foot of new snow at 4800’ that was a bit “upside-down” and was easily pushed on steep test slopes. Alpental Pro Patrol reported 6-8” soft slabs on the upper mountain with their morning control work and easy ski cut results on slopes at mid to lower elevations. In both instances, avalanches initiated within the new storm snow but showed the ability to gauge into deeper layers toward the Early March Crust. 

On Wednesday, the snow’s sensitivity to triggers should rely heavily on how the weather pans out. If the snow “locks up” due to cooling temperatures overnight, the ability to trigger a wet avalanche in the morning hours should decrease. That could change as filtered sunshine and springtime temperatures impact the zone later in the morning and into the afternoon. Conversely, if a poor freeze occurs overnight then you might be dealing with these issues right off the bat. Look to the snow surface to help you determine the likelihood of avalanches and make travel plans that can help you avoid being in consequential terrain if the snow is wet and heavy. Avalanches may be difficult to trigger but could run a long way on firm crusts and greased paths if they are initiated.

On upper elevation northerly slopes, weak facets were identified just above the Late March Crust prior to this event. We do not have any information at this time about how these weak grains may or may not have come into play during this storm. If they survived and you trigger an avalanche on them, it has the potential to fail in surprising ways by breaking above you or spanning far distances. Tread lightly in these areas and let us know what you find out there by submitting a public observation.

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