Bollettino valanghe

East Slopes North

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

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

In sintesi

An uptick in easterly winds could form wind-drifted slabs of snow where you might trigger an avalanche. Wind drifting could also increase the potential of triggering a larger avalanche on weak snow layers 1-2ft deep on northerly aspects. Steer around steep wind-drifted slopes below ridgelines and the base of cliffs, and avoid steep rollovers in rocky terrain with a shallow snowpack. 

Problemi valanghivi

  • Wind Slabs

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

    Winds have slowly increased over the last few days, and easterly winds will likely peak in the 10-20mph range on Tuesday. We don't expect wind slabs to be widespread, but you'll be able to find them in the usual spots, along ridgelines and below the base of cliffs. On southerly aspects, wind slabs are likely to be smaller but could be reactive, failing on melt-freeze crusts below the recent snow. More concerning is where winds drifted snow onto more northerly aspects, these slabs could step down into deeper, persistent weak layers, becoming large, widely propagating, and dangerous avalanches. 

    Identify wind-loaded slopes using visual clues such as cornice formations or textured surfaces and feel for stiff over weak snow. You can also use small, inconsequential test slopes to observe how the snow reacts. Cracking or mini avalanches are a sign you should avoid steep wind-loaded slopes. An observer on Feb. 9th triggered a small wind slab and was caught and carried on a southeast aspect that failed on a melt-freeze crust. Thankfully, no one was injured in the incident. 

    (2/9/2025)

    A small skier-triggered wind slab in the Cutthroat Drainage caught and carried a skier without injuries. 

    SE, 7100ft, SS-AS-R1-D1

  • Persistent Slabs

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

    The uptick in easterly winds might not seem like a significant weather event, but with our current weak, variable, and complex snowpack, it might not take much to increase the reactivity of these persistent slab avalanches. Sometimes, small weather inputs can significantly impact stability in these situations. And while we're not sure what the tipping point will be, we should be suspicious of additional loading events, even just a bit of wind. 

    We expect the most likely place to trigger a large persistent slab will be on northerly aspects in wind-drifted locations below ridgelines or the base of cliffs and steep terrain with exposed rocks where the snowpack tends to be shallower. The uppermost weak layer, the January Drought Layer, exists 1-2ft below the snow surface. Dig down and feel for stiffer, 4-finger, snow over surgery, weak facets. If you see signs of instability, like avalanches, whumpfing collapses, or shooting cracks, avoid steep slopes and put a large margin around complex terrain and large avalanche paths.

    Facets from December, buried 2-3 feet deep under old stiff wind slabs, are more isolated and unlikely. However, be aware of the potential consequences of a deep avalanche, particularly in wind-affected terrain with an unusually shallow snowpack above 6500ft.

    (2/7/2025)

    A natural avalanche that likely ran on the 4-5th. The wide propagation suggests that it could have ran on the January Drought Layer. 

    Photo: Katie Warren

Avalanche Discussion

Easterly winds will bump up again on Tuesday, peaking well into the snow transport range at 10-20mph.  Expect continued sunshine and cold temperatures, with extremely cold wind chill values, well below zero. So bundle up, bring some extra layers, face coverings, and hand warmers. These temperatures also mean that seemingly minor injuries, avalanches, or equipment malfunctions can quickly turn into a life-threatening situation. 

There's a lot of variability and complexity in layers that formed in the mid and upper snowpack since early December. With increased uncertainty, your best management strategy is to choose more conservative terrain. Consider the potential and consequences of triggering a large avalanche at middle and upper elevations, especially where facets formed and were preserved on northerly aspects. You can dig snowpits and use sudden or propagating tests to identify the problematic structure.

Over the past 10 days, 1-2ft of snow accumulated over this complex snowpack. However, both storm snow totals and total snow depths vary significantly throughout the zone. The last few days of sunny, cold weather have increased the likelihood of loose dry avalanches in steep terrain and formed a thin, breakable melt-freeze crust on southern aspects at mid and lower elevations. 

On Friday, observers investigated several slopes at middle and upper elevations. Near Cutthroat Lake (NNW, 6,780ft), they found small and large column test results (CTM(SC), PST 38/100 END) about 1.5 feet (50cm) below the surface, consistent with impressive shooting cracks reported by a party the day before. They also reported a couple of large natural slab avalanches at the base of cliffs and some small point releases in the surface snow.

Substantial evidence of the weak snowpack structure throughout the zone exists. Unfortunately, identifying a likely pattern of this current avalanche problem remains elusive. Over the past few days, a few avalanches have occurred, including natural wind slabs, skier-triggered avalanches, and cornice-triggered avalanches. These avalanches all occurred on northerly aspects, many at the base of cliffs. The JDL weak layer is widespread and present at most elevations. But at lower elevations, we don't have evidence showing that it's a current issue for triggering persistent slab avalanches. The overlying snow lacks cohesion or "slab" characteristics in many places. This structure may become more problematic with future storms or as the recent snow gains cohesion.

Less likely, but still a concern, are deeper layers of facets buried by older wind-drifted slabs during mid-December through mid-January. The distribution of this layering is more cryptic and complex but has been observed between 6,500-7,500ft in moderately wind-exposed terrain. An avalanche triggered on 2/1 near Cedar Creek/ Snagtooth Ridge shows an isolated area where this layer of mid-December facets was problematic. There are also slopes where you won't find the facets as they were melted or capped by a crust (high elevation rain event on Dec 7th) or blown away. 

You can help us gather more data by submitting an observation HERE or via the Avy App. 

Regioni coperte