Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Avalanche danger will remain heightened on Saturday as a warming trend capable of weakening the snowpack and cornices continues. Head for shaded slopes if the snow surface begins to get moist, keeping aware of hazardous terrain above you at all times.

Problemi valanghivi

  • Loose Wet

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

    Small Wet Loose avalanches and plenty of rollerballing have been observed the past few days as freezing levels have crept higher and sunny weather has impacted Snoqualmie Pass. The hazard has generally increased throughout the day as the sun’s warmth is able to overcome cool morning temperatures. Look for a similar pattern on Saturday, with avalanches more likely on slopes that receive direct sunshine. Wet Loose avalanches typically start at a point, such as near trees and rocks, and are capable of entraining lots of snow, triggering slabs, and traveling far distances as they descend. If you notice signs of these avalanches such as rollerballs, snow shedding from trees and rocks, or new avalanches with fan-shaped debris, then seek out shaded terrain away from sun-exposed slopes above you.

    (3/9/2021) Rollerballs and pinwheels were already observed within the zone the past few days with filtered sunshine. On Thursday, we expect to see more of these and some actual Wet Loose avalanches due to more sunshine and rising freezing levels. [Photo: Enji Cooper]

Avalanche Discussion

Saturday will be the third day in a row of a warming trend that has seen more sunshine and higher freezing levels each day.  We could see some clouds make their way into the zone by day’s end, but the freezing level will approach 7500’, the warmest of the period. These warm temperatures will help to minimize an overnight freeze on Friday night and could speed up the destabilization of the snow surface on Saturday. Warm-ups, like we are experiencing, are capable of weakening the snowpack and cornices, creating avalanches. The timing can be a little tricky to pin down, and many slopes that have not yet reached their tipping point could be primed for human triggers or the additional warming to put them over the edge on Saturday. Continue to give cornices a wide berth by not traveling on or below them and if you see large crevasse-like cracks in the snow, avoid slopes below them.

At higher elevations on slopes that don’t see direct sunshine, there may still be cold dry snow that could be reactive on steep or rocky terrain. Before stepping into aggressive terrain, you should take a minute to look for wind-loaded features or a poor bond to the 3/5 crust.

We have decided to remove the Deep Persistent Slab problem from our official problem list at Snoqualmie Pass. Although the weak snowpack structure remains, a few data points have made us feel more comfortable with this layer than we have recently.

  1. Our last confirmed natural avalanche on the Mid-January crust/facet layer at Snoqualmie Pass was over a week ago. (The Chair Peak slide on 2/28-3/1). The last suspected avalanche on this layer throughout the region may have been a few days later in the West South.
  2. We have a generally strong and well-settled upper snowpack above this layer. This includes the most recent 3/5 crust, which is thick and supportable in most locations throughout the zone.
  3. Since our last major loading event on this layer, test results have become more inconsistent than they were previously. 

The Mid-January crust still remains 8-10 feet deep in the snowpack throughout much of the zone, and we believe it is currently dormant. It may wake back up at some point this season, however. At that point, we will put it back on the official problem list and continue to talk about the dangers this layer presents. Until that time, don’t forget about this layer. If you choose to enter more complex or large avalanche terrain, you should continue to talk with your partners about the low-likelihood/high consequence avalanches this layer is capable of producing. Keep in mind that when they occur, these avalanches have broken trees and descended far distances toward their maximum runouts in valley bottoms. The best way to mitigate your risk is to limit your time in and below large avalanche start zones, paths, and runouts. 

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