Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

Continued snow and wind are stressing a weak snowpack and creating increasingly dangerous avalanche conditions. You could trigger very large avalanches that break widely across terrain. The only way to safely manage this tricky snowpack is to avoid traveling on or under slopes over 30 degrees at mid and upper elevations.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–2.5

    Another round of snow and wind continues to stress a very weak snowpack. Triggering large persistent slab avalanches that break widely 2-4ft deep is increasingly likely with additional snow. The most concerning slopes will be at mid and upper elevations, particularly in leeward terrain where the winds drift the snow deeper. However, you should treat any steep slope as suspect.

    Over the last week, there have been six close calls and one fatality involving this layer of weak-faceted snow over the Early February Crust. The most recent close call was Saturday near Longs Pass, where a skier triggered a very large avalanche and was caught and carried but miraculously only partially buried and uninjured. (Other avalanche incident details in the discussion) Many of these observations indicate that the slope had already been skied/ridden once or multiple times before the avalanche occurred. It could be the 2nd, 3rd, or 8th person on the slope that triggers it. While this reactivity is unusual for Washington, it is typical for this avalanche problem. 

    These avalanches are propagating widely and being remotely triggered from low-angle terrain below or adjacent to steep slopes. You might not receive signs of instability before the whole slope fails.  Avoid traveling on slopes over 30 degrees. This problem requires patience, conservative terrain selection, and maintaining wide margins between you and steep overhead terrain.

    (3/9/2024)

    A very large persistent slab avalanche triggered by a skier near Long Pass. They were the second skier on the slope when the avalanche occurred. The skier was caught, carried, and partially buried but uninjured. 

    W aspect, 6400ft, crown depth 2-3ftHS-ASu-R3-D3-O

  • Wind Slabs

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

    Increasing winds and a few inches of new snow could form fresh wind slabs near ridgelines, steep gullies, and the base of cliffs. We're most concerned about this problem at elevations above around 4000ft, with notably more snow over the Early February Crust. While these avalanches may start small, they may be likely to step down to deeper weak layers, become very large, and break widely.Look for actively blowing snow, cornice formations, and textured surfaces to identify likely areas for wind slabs. Avoid steep terrain where you identify stiff wind-transported snow.

    (3/10/2024)

    A skier triggered this small fresh wind slab on Sunday near Blewett Pass.

    HS-ASu-R1-D1-I

    Photo: Steven R.

Avalanche Discussion

NWAC will be closed on Tuesday, March 12th, as we gather and grieve following the death of one of our forecasters, Matt Primomo. We will not issue regular avalanche or mountain weather forecasts on Tuesday. We will return to normal operations on Wednesday, March 13th. We appreciate the community's understanding and support during this time.

Discussion:Moderate snow will taper off in the morning, only to return by late afternoon or evening. It doesn't take much new snow or wind-loading to tip the scales on this tricky snowpack, so choose conservative terrain that accounts for the continued increase in avalanche danger. 

This pattern of persistent slab problems can be challenging for backcountry decision-making. It takes conservative terrain management and diligent patience. Stepping into steep terrain at mid and upper elevations is simply just a game of chance; you may get away with it, or you could trigger a very large avalanche that is likely to injure or kill you. The structure is especially apparent in the eastern Cascades, where the snowpack is generally more shallow than at the crest. So, if you're venturing into these eastern zones, be prepared to take a step back in your typical terrain selection and understanding of the snowpack.

On Thursday, forecasters toured near Blewett Pass. We could see the recently triggered avalanche in Owl Creek (Blewett Pass) from a distance, and they found variable test results that showed the persistent slab problem lingering. Tests and layer characteristics indicated that weak layers are slowly gaining strength. Our snowpack is complicated due to the intermittent dry spells in February. Besides the early February Crust, there are also potential layers of surface hoar and faceted grains from the 14th, 18th, and 24th. Widely propagating avalanches could fail on any of these layers. Approach the mountains cautiously and enjoy some low-angle powder until these weak layers gain strength.

Summary of Recent Avalanche Incidents: In addition to the avalanche incident on Saturday, there have been nearly daily reports of close calls on this persistent weak layer. On Thursday, snowbikers remotely triggered two very large avalanches in the Teanaway, and there was a close call with a skier who was caught and carried in an avalanche on the S aspect of Van Epps Peak. Earlier in the week, snowmobilers triggered large avalanches around the Blewett Pass area, and a skier was partially buried with minor injuries in an avalanche on a NW aspect of Jim Hill in the neighboring Stevens Pass zone. Last Saturday, a snowmobiler was buried and did not survive an avalanche near Darland Mountain in the East South zone. 

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