Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
1 · Faible
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Strong winds along with very light snowfall may create isolated wind slabs near and above treeline Sunday.  If freshly drifted snow at higher elevations is more widespread or deeper than forecast, use caution on slopes steeper than 35 degrees.  Other considerations to keep in mind are areas where you find slick surface crusts and shallow coverage like in the Wenatchee Mountains.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1

    A weather system moving through Sunday morning will kick up strong ridgeline winds but likely only produce 1-3" of snow near the Cascade crest and above 4500' with lower amounts further east and at lower elevations.  If you find more than a few inches of new snow in wind-sheltered locations Sunday,  fresh wind slabs may have formed on lee slopes and be more widespread than anticipated near and above treeline.  Where you see overhanging cornices and fresh wind drifts, use caution on steep slopes with similar features.  Consider the consequences of a small avalanche near terrain traps like cliff bands. Give recently formed cornices a wide berth if traveling along ridgelines. 

    Example of intense wind loading off a ridgeline.

Avalanche Discussion

From January 11th to 13th a major storm delivered heavy snow and rain to the East Central zone. The Sasse Ridge Snotel picked up almost 5" of water(!) over the event.  Over 2' of new snow fell before the switch to rain on the 12th.  Further east, Mission Ridge followed a similar temperature and precipitation type trend but only tallied 2.5" of water over the same period.  Large and destructive avalanches ran on the 12th, both as storm slabs and later as wet avalanches. Observations were limited during the cycle but in adjacent zones, the activity was well documented.  Forecasters visited Stevens Pass on Tuesday, 1/12 and every avalanche path had at least one, if not multiple avalanches in it. On Washington Pass, observers reported avalanches up to D3 in size (big enough to break mature timber and bury cars) including an avalanche that hit a closed portion of Highway 20, below Delancey Ridge. 

Deeper weak layers exist in areas with a shallow snowpack, such as the Wenatchee Mountains. On Thursday, forecasters traveled south of Blewett Pass and found about 2.5 - 4 feet of snow on the ground with a number of hard crusts over weaker faceted snow from December.  While snowpack tests suggested there was a potential for avalanches to propagate widely on the December facets, overlying stout crusts above the weak layer make this unlikely. In addition, no new or recent avalanches releasing down to these deeper weak layers have been reported. 

More recently, winds, periods of sunshine, and milder temperatures have left a variety of snow surfaces throughout the terrain. Use caution near steep slopes where you find a firm and slick surface crust. Either move to lower angled terrain or make sure you can self-arrest a fall. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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