Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sat
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

The heaviest snowfall is behind us, but you could still trigger large avalanches on deeply buried weak layers. These avalanches can break widely and run long distances. Signs of instability are not always obvious with these avalanche conditions. Your best option for avoiding triggering one of these destructive slides is to avoid traveling on or directly 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

    While smaller storm and wind slabs may also linger, the real problem lies deeper in the snowpack. Weak, faceted snow over the Early February Crust has 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. After the recent storms, a thicker slab exists over this weak layer, so avalanches could 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. The best way to identify this deceptive avalanche problem is with snow profiles and snowpack tests. But with variability across the terrain, these too can be misleading. Rather than assess your way into steep terrain, the best way to stay out of harm's way is to avoid traveling on or under slopes over 30 degrees. Give this problem wide safety margins. 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. At lower elevations, heavy rain likely created a thick, slippery crust 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

Avalanche Discussion

You're not alone if you feel like we've been in a perpetual pattern of persistent slab problems. Lower-than-average snowfall and warmer-than-average temperatures contribute to crust formation and a shallow snowpack prone to developing these tricky weak layers. The issue is especially apparent in the eastern Cascades this winter. So, if you're venturing into these eastern zones this winter, be prepared to step into what can feel like a very unfamiliar snowpack compared to what we typically experience in the Cascades. 

If the sun comes out to stay for a while in the afternoon on Friday, 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. 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 reported triggering wind slabs that stepped down to the EFC and propagated widely during avalanche mitigation work. Our snowpack has become complicated throughout 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