Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The chance for very large and unsurvivable avalanches will maintain dangerous avalanche conditions. Warming temperatures and sun could set off wet avalanches or even large cornice fall. Continue to avoid traveling on or under large open slopes, steep sparsely treed terrain, and areas that received recent wind drifting.

Problèmes avalancheux

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3

    Very large, natural avalanches have occurred as recently as Sunday or Monday with more recent avalanches in other zones. Deep persistent avalanches can destroy cars and houses and occur with no warning. An avalanche would be unsurvivable if you were caught while recreating on foot or on a snow machine. Even avalanche professionals with decades of experience have trouble predicting these avalanches and accurately make decisions about them. Thursday's warm temperatures and sun will add another layer of uncertainty to this equation.  A concern with the warming is the chance for large cornices to fall which could, in turn, trigger these destructive avalanches. Avoid slopes with overhead cornices. Make sure not to travel on overhung snow on leeward sides of ridges. 

    The way to stay safe is simple: Avoid traveling in or under large avalanche paths. Avoid leeward slopes 35 degrees and steeper where the wind drifted slabs in the past week. Use extra caution on any steep slope, even around sparse trees. Before you commit to traveling in avalanche terrain, ask yourself, "What's the largest avalanche that this slope can produce, am I willing to take that risk, and is there a safer option?"

    (3/1/2021) A very large avalanche (D3) was triggered by WSDOT highway forecasters on March 1st in a portion of the West Camp path on Rock Mtn. Adjacent sections of this avalanche path ran naturally on Feb 26th. Photo: WSDOT

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Another day of warm temperatures and sun could be enough to see wet avalanches on slopes that have yet to slide in the past couple of days. If slopes are getting soft and wet, move to lower-angle and more shaded terrain. These avalanches are normally easy to manage. With the complexity of dangerous conditions on Thursday, it's best to stay off of slopes prone to these avalanches.

    Wednesday night will stay warm with freezing levels hovering at 4,500ft. During the day, cloud cover and wind will also be factors determining the likelihood of wet avalanches. Pay attention to how soft surfaces are and if the snow has melted enough to slide downhill. 

    (3/1/2021) Small point releases originating from rocks near the Bomber Chutes, just outside of the Mission Ridge ski area boundary at 6,200ft on an E aspect. These likely ran on Feb 27th or 28th. Photo: Josh Hirshberg

Avalanche Discussion

The warm temperatures Wednesday night into Thursday are concerning given that we're less than 3 days out from the last known deep slab avalanche. Other factors like cloud cover and wind could determine the extent of melting or warming of the snowpack.  Given the bounty of uncertainty already at play with avalanche conditions, forecasters remain concerned about the potential for more very large avalanches. We're in a prolonged period of historically unstable conditions and dealing with a weak layer that is challenging to even seasoned professionals. The deep slab problem continues to pose high consequences and demands conservative terrain and travel choices. 

February 25-26th brought a storm with near to 2" of water equivalent at the Cascade Crest and extreme winds. This came on the heels of an even bigger storm. From the 20-23rd a massive storm brought up to 6" of water equivalent to the mountains near the crest but much less to the Wenatchee Range further east. Numerous deep and very wide avalanches (Many D3-3.5's, some size D4's)  ran on, or around the 22nd in the mountains near the crest, and some deeper slabs were reported from the Wenatchee Range. Similar avalanches have continued into this week. While conditions may be less dangerous in parts of the Wenatchee Mountains, due to less recent snow, the same weak layers can be found and recent avalanches have been triggered on them. 

Recent notable avalanches:

3/1: WSDOT avalanche teams observed a recent (within the past 24hrs) natural D3.5 deep slab from high, north-facing terrain in the Chiwaukum Range. They also triggered an 8ft deep D3 in southeast facing terrain at around 6,000ft off Rock Mountain east of Stevens Pass (the remaining hangfire in West Camp path). Chair Peak at Snoqualmie Pass ran as a D3.5 at some point between Sunday night and Monday morning with a crown 10-15'+ deep. An observer reported numerous very large avalanches near Fortune Peak, just west of this zone.

2/28: A fairly fresh-looking deep persistent slab avalanche from upper elevation terrain was spotted in the Chiwawa drainage. 

2/26-27: A natural D4 avalanche released from Rock Mtn and came just short of Highway 2. A couple of D2.5-3's terrain in Icicle Creek (see photo below).

2/24: A deep persistent slab occurred on a south aspect near Manastash Ridge. 

 

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