Bollettino valanghe

Olympics

Northwest Avalanche Center
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Tue
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In sintesi

Take note of how the snow surface is changing throughout the day due to the sun’s influence. When it starts to get sticky and wet or you notice snow shedding from trees and rocks, you should change your focus from dry avalanches toward wet avalanches and head toward shaded slopes.

Problemi valanghivi

  • Loose Wet

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    Probabilità
    Likely
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    1

    As temperatures creep up and the sun grows stronger throughout the day, expect wet avalanches to become more prominent on steep sunny slopes. Your first indicators that the upper snowpack is destabilizing will be rollerballs and pinwheels, snow shedding from trees and rocks, and the surface becoming wet and sticky. If you notice these signs, expect Wet Loose avalanches to follow and head toward shadier slopes. These slides often start at a point such as near trees or rocks, can entrain significant snow, and will fan out as they descend, possibly traveling long distances toward lower elevations. 

    (2/28/2021) Rollerballs such as this will be one of your first indicators that the snow is destabilizing and Wet Loose avalanches may follow.

  • Wind Slabs

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    Probabilità
    Possible
    Dimensione
    1

    Plenty of wind-affected snow still exists as you ascend in elevation, and cold dry snow will be more likely to escape the sun’s influence on northerly slopes later in the day. Take a look for freshly built cornices, textured snow surfaces, or new drifts behind trees or other objects to help you identify wind-loaded slopes to avoid. Wind Slabs could be hidden under a couple of inches of fresh snow, so feel for subtle changes as you travel to help you determine if you stumbled upon one without knowing. Wind Slabs will be more likely near rocky features such as the confined gullies or at the base of cliffs, on leeward slopes near ridgelines, or on convex rollovers. You can use uptrack tests or test slopes to determine how the recent storm snow is reacting to your weight and if slab potential exists. If you find poorly bonded snow or suspect terrain to be wind-loaded, you should seek out lower-angled slopes. 

    (4/10/2021) Multiple human-triggered avalanches occurred at Hurricane Ridge on Saturday (4/10). These slides were 6-12" deep and were running easily on the recent crusts [E 5400' Photo: Joe Carpenter]

Avalanche Discussion

The upper snowpack at Hurricane Ridge is defined by two crusts and recent storm snow. The first crust (4/9) should be about 5-8" below the surface on slopes that typically see direct sunshine, or you could even find it on the surface in wind-exposed locations. On shadier slopes, this interface may present as more of a density break than a defined crust. As you look deeper in the snowpack, you'll come to the 4/7 interface which should be about a foot below the surface. This stout crust should exist on all aspects and be easily identifiable. We expect all avalanche activity on Monday to occur above the 4/7 interface, whether the avalanche has wet or dry characteristics. Avalanches have the ability to run far and fast on this crust and could initially fail at either interface. Although we lack recent observations from other areas of the Olympics, we suspect that a similar snowpack structure exists in many locations. 

Monday should be the start of what projects to be a multi-day shedding event/wet avalanche cycle in the Olympic Mountains as the snowpack transitions from cold and dry to warmer and wetter. The timing of these transitions can be difficult to pin down, and your morning concerns could be more focused on dry avalanche problems such as Wind Slabs or Dry Loose. As the sun gains influence and warms surfaces, the transition to wet avalanche problems may happen quickly, manifesting in different types of avalanches. Snow will start to shed from trees and rocks, falling onto the slopes below and possibly triggering Wind Slabs or starting loose avalanches - either wet or dry. Both fresh and mature cornices exist throughout the zone and could fall under the sun’s influence, triggering slabs or starting loose slides. The sun could even cause the recent snow to "slab up" and become more reactive on steep slopes. This will be the pattern throughout the week as temperatures creep higher and the strong April sun destabilizes the recent cold dry snow. 

Wet avalanches are generally not well understood and are difficult to predict, so it could take a few days for all of these scenarios to play out. But Monday should be the start and you should keep in mind that multiple near-misses and avalanche involvements have occurred around the Cascades over the past week as we have navigated flip-flopping springtime weather. You can read about the most recent involvement where a skier was fully buried at Snoqualmie Pass here. This recent history combined with the uncertainty around these shedding events should lead you toward a more conservative mindset and terrain selection.

Spring Forecast Schedule:  NWAC will issue a danger rating every day for the Olympics beginning Friday, April 2nd  - Sunday, April 18th. 

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.

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