Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

A weak snowpack structure, new snow, and wind will quickly create dangerous avalanche conditions. You could trigger very large avalanches that break widely across terrain. 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

    We expect that the forecasted 4-6" of new snow and moderate winds will be enough to overload this weak snowpack structure. Triggering large persistent slab avalanches that break widely 2-4ft deep will be more likely as we put stress on the snowpack from 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. While this reactivity is unusual for Washington, it is typical for this avalanche problem. These avalanches are failing 2-4ft deep, 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. It could be the 2nd, 3rd, or 8th person on the slope that triggers it. 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
    Possible
    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.

    (3/7/2024)

    Pillow-like drifts and textured surfaces like in this photo are a good visual clue of wind slabs.

    Photo: Katie Warren

Avalanche Discussion

NWAC is devastated to report the death of one of our Avalanche Forecasters, Matt Primomo. Tragically, Matt passed away in a non-avalanche accident away from work on Thursday, March 7th. Matt has been a key member of the NWAC family since 2017. His life in the mountains touched so many people. We are absolutely heartbroken. Please join us as we mourn this immense loss with Matt’s family, friends, and community.

Discussion:Increasing precipitation and wind will quickly heighten avalanche concerns. We may see some rain at the very lowest elevations, making small wet loose avalanches or rollerballs possible. 

This pattern of persistent slab problems can be challenging for backcountry decision-making. It takes conservative terrain management and diligent patience. 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: 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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