Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions still exist, and you are likely to trigger large avalanches on deeply buried weak layers. These avalanches can break widely and run long distances. Signs of instability are not always obvious, so your best option for avoiding triggering one of these destructive slides is to avoid traveling on or under slopes greater than 30 degrees.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–3

    Weak, faceted snow over the Early February Crust created a tricky and dangerous persistent slab problem throughout much of the East Central Zone. Multiple human-triggered and natural avalanches have failed on this persistent weak layer. On Friday, an avalanche incident in East South zone likely involved this layer of facets over the Early February Crust (EFC). A preliminary report is in the discussion below. After the recent storms, a thicker slab exists over this weak layer, so avalanches will likely be much larger. A smaller avalanche could also step down to this layer. You can trigger a persistent slab avalanche from low-angle terrain below or adjacent to steep slopes, and they may propagate widely across terrain. You may or may not observe signs of instability, like collapsing, before triggering an avalanche, and it may not be the first person on the slope to trigger it. 

    Avoid traveling on or under slopes over 30 degrees. Give steep open slopes wide safety margins. These are not conditions where you can manage the hazard on a small feature scale, as large slopes can fracture at once, running through lower-angle benches and small features. Stay off of and out from underneath steep slopes at elevations above approximately 4500ft, where 1-3ft of new snow has accumulated since 2/24. Heavy rain likely created a thick, slippery crust at lower elevations and will limit avalanche potential.

    (2/28/2024)

    This remotely triggered avalanche in the Teanaway Drainage failed on facets over the Early February Crust. 

    5600ft, NEE aspectHS-ASr-R3-D2-O

    Photo: Mike Elges

  • Wind Slabs

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

    With continued light snowfall and cold temperatures, there is plenty of low-density snow to drift around. Moderate winds formed stiff wind slabs near ridgelines and in exposed terrain. These smaller avalanches can step down to deeper weak layers, quickly becoming very large and potentially unsurvivable. Textured surfaces, cornice formations, and drifts around rocks and trees can all point to likely wind-loaded slopes. With these overlapping avalanche problems, it will be best to simply avoid steep terrain, especially in wind-affected areas. 

    (1/6/2024)

    An example from late December of a wind slab that stepped down to deeper weak layers. 

    SS-AS-R2-D2-O

    Photo: Max Steed

Avalanche Discussion

Preliminary Report: An avalanche accident occurred on Friday, March 1, near Darland Mt in the Ahtanum Meadows area. Two snowmobilers were involved in the slide. One rider was fully buried and killed. The avalanche occurred around 6600ft in a generally east-facing bowl. NWAC staff will visit the accident site on Saturday. Our deepest condolences to the family, friends, and community.

This pattern of persistent slab problems can be incredibly challenging for backcountry decision-making. It takes extremely conservative terrain management and patience. This winter's lower-than-average snowfall and warmer-than-average temperatures contribute to a shallow snowpack prone to developing these tricky weak layers. The issue is especially apparent in the eastern Cascades, which, on a typical year, is already a bit shallower and weaker than areas west of the crest. So, if you're venturing into these eastern zones this winter, be prepared to take a step back in your typical terrain selection and understanding of the snowpack. It's easy to be surprised in these conditions, so with the increased complexity of the snowpack, choose low-angle terrain to enjoy the fresh snow. 

If the sun comes out to stay for a while in the afternoon, you may see some small, wet loose avalanches, rollerballs, and pinwheels. 

Over the past few days, forecasters and observers throughout the Wenatchee Mountains, the Teanaway, Salmon La Sac, and near Leavenworth have all found a weak snowpack structure. Snowpack tests consistently produce results that indicate triggering a persistent slab avalanche is likely. A large, natural avalanche near Van Epps Pass occurred earlier this week. Observers on Dirtyface, Long Pass, and Salmon La Sac have also reported whumphing collapses on the facets above the Early February Crust (EFC). On Thursday, the Mission Ridge Pro Patrol triggered wind slabs that stepped down to the EFC and propagated widely during avalanche mitigation work. Our snowpack is complicated due to the intermittent dry spells in February. 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. But be patient, as it could be a while before we see improved snow stability. 

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here.  

Regioni coperte